Tue·Feb 23, 2021Tuesday·February 23, 2021

1. 01*

   Axion-matter coupling in multiferroics

   Henrik S. Røising🇸🇪 · Benjo Fraser🇸🇪 · Sinéad M. Griffin🇺🇸 · Sumanta Bandyopadhyay🇸🇪 · Aditi Mahabir🇺🇸 · Sang-Wook Cheong🇺🇸 · Alexander V. Balatsky🇺🇸

   Multiferroics (MFs) are materials with two or more ferroic orders, like spontaneous ferroelectric and ferromagnetic polarizations. Such materials can exhibit a magnetoelectric effect whereby magnetic and ferroelectric polarizations couple linearly, reminiscent of, but not identical to the electromagnetic $\mathbf{E}\cdot \mathbf{B}$ axion coupling. Here we point out a possible mechanism in which an external dark matter axion field couples linearly to ferroic orders in these materials without external applied fields. We find the magnetic response to be linear in the axion-electron coupling. At temperatures close to the ferromagnetic transition fluctuations can lead to an enhancement of the axion-induced magnetic response. Relevant material candidates such as the Lu-Sc hexaferrite family are discussed.

   hep-phcond-mat.mes-hallcond-mat.mtrl-scicond-mat.str-elPRResearch(2021)·28 citations
2. 02*

   Neutrinos in Astrophysics and Cosmology: Theoretical Advanced Study Institute (TASI) 2020 Lectures

   Kevork N. Abazajian🇺🇸

   I introduce the consequences of neutrino mass and mixing in the dense environments of the early Universe and in astrophysical environments. Thermal and matter effects are reviewed in the context of a two-neutrino formalism, with methods of extension to multiple neutrinos. The observed large neutrino mixing angles place the strongest constraint on cosmological lepton (or neutrino) asymmetries, while new sterile neutrinos provide a wealth of possible new physics, including lepton asymmetry generation as well as candidates for dark matter. I also review cosmic microwave background and large-scale structure constraints on neutrino mass and energy density. Lastly, I review how X-ray astronomy has become a branch of neutrino physics in searches for keV-scale sterile neutrino dark matter radiative decay.

   hep-phastro-ph.COPoS(2021)·13 citations
3. 03*

   Entanglement and Many-Body effects in Collective Neutrino Oscillations

   Alessandro Roggero🇺🇸

   Collective neutrino oscillations play a crucial role in transporting lepton flavor in astrophysical settings, such as supernovae, where the neutrino density is large. In this regime, neutrino-neutrino interactions are important and simulations in the mean-field approximation show evidence for collective oscillations occurring at time scales much larger than those associated with vacuum oscillations. In this work, we study the out-of-equilibrium dynamics of a corresponding spin model using Matrix Product States and show how collective bipolar oscillations can be triggered by many-body correlations if appropriate initial conditions are present. We find entanglement entropies scaling at most logarithmically in the system size suggesting that classical tensor network methods could be efficient in describing collective neutrino dynamics more generally. These observation provide a clear path forward, not only to increase the accuracy of current simulations, but also to elucidate the mechanism behind collective flavor oscillations without resorting to the mean field approximation.

   hep-phastro-ph.HEnucl-thPRD(2021)·71 citations
4. 04*

   Long-term LHC Discovery Reach for Compressed Higgsino-like Models using VBF Processes

   Cardona Natalia🇨🇱 · Flórez Andrés🇨🇱 · Gurrola Alfredo🇺🇸 · Johns Will🇺🇸 · Sheldon Paul🇺🇸 · Tao cheng🇺🇸

   The identity of Dark Matter (DM) is one of the most active topics in particle physics today. Supersymmetry (SUSY) is an extension of the standard model (SM) that could describe the particle nature of DM in the form of the lightest neutralino in R-parity conserving models. We focus on SUSY models that solve the hierarchy problem with small fine tuning, and where the lightest SUSY particles (${\tilde{\chi }}_1^0$, ${\tilde{\chi }}_1^{\pm }$, ${\tilde{\chi }}_2^0$) are a triplet of higgsino-like states, such that the mass difference $\Delta m({\tilde{\chi }}_2^0,{\tilde{\chi }}_1^0)$ is 2-50 GeV. We perform a feasibility study to assess the long-term discovery potential for these compressed SUSY models with higgsino-like states, using vector boson fusion (VBF) processes in the context of proton-proton collisions at $\sqrt{s}=13$ TeV, at the CERN Large Hadron Collider. Assuming an integrated luminosity of 3000 fb${}^{-1}$, we find that stringent VBF requirements, combined with large missing momentum and one or two low-$p_T$ leptons, is effective at reducing the major SM backgrounds, leading to a 5$\sigma$ (3$\sigma$) discovery reach for $m({\tilde{\chi }}_2^0)<180$ $(260)$ GeV, and a projected 95\% confidence level exclusion region that covers $m({\tilde{\chi }}_2^0)$ up to 385 GeV, parameter space that is currently unconstrained by other experiments.

   hep-phJHEP(2022)·14 citations
5. 05*

   $\tilde{\nu }$ contributions to electron and muon EDM in an Inverse Seesaw Mechanism

   J.S. Alvarado🇨🇴 · R. Martinez🇨🇴

   A non-universal anomaly free $U(1{)}_X$ extension to the Minimal Supersymmetric Standard Model, consisting of four scalar doublets, four scalar singlets and additional quark and lepton singlets including right-handed and Majorana neutrinos, is used to determine the contributions to the electron and muon Electric Dipole Moment. The additional CP violation sources come from the lepton sector, where neutrino masses are explained by an Inverse Seesaw Mechanism and the CP violating phase of the PMNS matrix generates complex interactions that involves exotic neutrino and sneutrino mass eigenstates. Such contributions are studied at one and two-loop level by considering the associated Barr-Zee diagrams and their supersymmetric counterpart. At one-loop level, it is found that the Electric Dipole Moment fixes a relationship between chargino and sneutrino masses depending on which particles have a mass bellow $10^6$ GeV. At two loop level, contributions are comparable to the one-loop contributions but the integrals diverge in some cases, yielding additional restrictions such as no degenerate sneutrino masses and they should be heavier than chargino masses.

   hep-ph1 citation
6. 06*

   Possible implications for particle physics by quantum measurement

   Xiang Lv🇨🇳 · Jun Jing🇨🇳

   In sharp contrast to its classical counterpart, quantum measurement plays a fundamental role in quantum mechanics and blurs the essential distinction between the measurement apparatus and the objects under investigation. An appealing phenomenon in quantum measurements, termed as quantum Zeno effect, can be observed in particular subspaces selected by measurement Hamiltonian. Here we apply the top-down Zeno mechanism to the particle physics. We indeed develop an alternative insight into the properties of fundamental particles, but not intend to challenge the Standard Model (SM). In a unified and simple manner, our effective model allows to merge the origin of neutrino's small mass and oscillations, the hierarchy pattern for masses of electric charged fermions, the color confinement, and the discretization of quantum numbers, using a perturbative theory for the dynamical quantum Zeno effect. Under various conditions for vanishing transition amplitudes among particle eigenstates in the effective model, it is remarkable to probe results that are somewhat reminiscent of SM, including: (i) neutrino oscillations with big-angle mixing and small masses emerge from the energy-momentum conservation, (ii) electrically-charged fermions hold masses in a hierarchy pattern due to the electric-charge conservation, (iii) color confinement and the associated asymptotic freedom can be deduced from the color-charge conservation. We make several anticipations about the basic properties for fundamental particles: (i) the total mass of neutrinos and the existence of a nearly massless neutrino (of any generation), (ii) the discretization in quantum numbers for the new-discovered electrically-charged fermions, (iii) the confinement and the associated asymptotic freedom for any particle containing more than two conserved charges.

   hep-phquant-ph0 citations
7. 07*

   Effects of $N(2000){5/2}^{+}$ on $\gamma p\to K^{+}\Lambda (1405)$

   Yu Zhang🇨🇳 · Fei Huang🇨🇳

   The photoproduction reaction of $\gamma p\to K^{+}\Lambda (1405)$ is investigated based on an effective Lagrangian approach at the tree-level approximation with the purpose of understanding the reaction mechanism and extracting the resonance contents and the associated resonance parameters in this reaction. Apart from the $t$-channel $K$ and $K^{\ast }$ exchanges, $s$-channel nucleon ($N$) exchange, $u$-channel $\Sigma$, $\Lambda$, and $\Lambda (1405)$ exchanges, and generalized contact term, the exchanges of a minimum number of $N$ resonances in the $s$ channel are taken into account in constructing the reaction amplitudes to describe the experimental data. It is found that by introducing the $N(2000){5/2}^{+}$ resonance exchange in the $s$ channel, one can reproduce the most recent differential cross-section data from the CLAS Collaboration quite well. Further analysis shows that the cross sections of $\gamma p\to K^{+}\Lambda (1405)$ at high energies are dominated by the $t$-channel $K$ exchange, while the contributions from the $s$-channel $N$ and $N(2000){5/2}^{+}$ exchanges are rather significant to the cross sections in the near-threshold energy region. Predictions for the beam and target asymmetries for $\gamma p\to K^{+}\Lambda (1405)$ are given.

   hep-phnucl-thPRC(2021)·10 citations
8. 08*

   Soft supersymmetry breaking terms and lepton flavor violations in modular flavor models

   Tatsuo Kobayashi🇯🇵 · Takashi Shimomura🇯🇵 · Morimitsu Tanimoto🇯🇵

   We study the soft supersymmetry (SUSY) breaking terms due to the modulus F-term in the modular flavor models of leptons. It is found that the soft SUSY breaking terms are constrained by the modular forms, and specific patterns are derived. Those phenomenological implications are discussed in such as the lepton flavor violation, $\mu \to e+\gamma$ decay. In order to examine numerically, two modular flavor $A_4$ models are taken. The SUSY breaking scale is significantly constrained by inputting the observed upper bound of the $\mu \to e+\gamma$ decay. The SUSY mass scale is larger than around $8$ TeV and $5$ TeV for the two $A_4$ models, respectively. Therefore, the current experimental upper bound for the $\mu \to e+\gamma$ decay corresponds to the new physics of the SUSY particle at the $5$ -- $10$ TeV scale in the modular flavor models. The predicted branching ratio depends on a modulus $\tau$ significantly. It decreases of one order at the large $\mathrm{Im}\tau$. We also calculate the branching ratios of tauon decays to $e+\gamma$ and $\mu +\gamma$. Predicted ones are at most $\mathcal{O}(10^{-15})$, which are much below the current experimental bounds.

   hep-phhep-thPLB(2021)·17 citations
9. 09*

   Correlation between the scaling factor of the yukawa coupling and cross section for the $e^{+}{e}^{-}\to hhf\overline{f}$ ($f\ne t$) in type-I 2HD

   Ijaz Ahmed🇵🇰 · Sehrish Gul🇵🇰 · Taimoor Khurshid🇵🇰

   The objective of this study is to correlate the scaling factor of the Standard Model (SM) like Higgs boson and the cross section ratio of the process $e^{+}{e}^{-}\to hhf\overline{f}$ where $f\ne t$, normalized to SM predictions in the type I of the Two Higgs Doublet Model. All calculations have been performed at $\sqrt{s}=500$ GeV and $1\le \tan \beta \le 30$ for masses $m_H=m_A=m_{H^{\pm }}=300GeV$ and $m_H=300$ GeV, $m_A=m_{H^{\pm }}=500$ GeV. The working scenario is by taking without alignment limit, that is $s_{\beta -\alpha }=0.98$ and $s_{\beta -\alpha }=0.99,$ $0.995$, which gives the enhancement in the cross section, particularly a few times greater than the predictions of the SM due to resonant-impacts of the additional heavy neutral Higgs bosons. This shows that enhancement in cross section occurs on leaving the alignment i.e., $s_{\beta -\alpha }=1$, at which all the higgs that couple to vector bosons and fermions have the same values as in SM at tree level. A large value of enhancement factor is obtained at $s_{\beta -\alpha }=0.98$ compared to $s_{\beta -\alpha }=0.99,$ $0.995$. Furthermore, the decrease in the enhancement factor is observed for the case when $m_H=300$ GeV, $m_A=m_{H^{\pm }}=500$ GeV. The behavior of the scaling factor with $\tan \beta$ is also studied, which shows that for large values of $\tan \beta$, the scaling factor becomes equal to $s_{\beta -\alpha }$. Finally a convincing correlation is achieved by taking into account, the experimental and theoretical constraints e.g, perturbative unitarity, vacuum stability and electroweak oblique parameters.

   hep-phInt.J.Theor.Phys.(2021)·2 citations
10. 10*

    Investigation of the stability for fully-heavy $bc\bar{b}\bar{c}$ tetraquark states

    Zi-Yan Yang🇯🇵 · Qi-Nan Wang🇨🇳 · Wei Chen🇨🇳 · Hua-Xing Chen🇨🇳

    We study the existence of fully-heavy hidden-flavor $bc\bar{b}\bar{c}$ tetraquark states with various $J^{PC}=0^{\pm +},0^{--},1^{\pm \pm },2^{++}$, by using the moment QCD sum rule method augmented by fundamental inequalities. Using the moment sum rule analyses, our calculation shows that the masses for the S-wave positive parity $bc\bar{b}\bar{c}$ tetraquark states are about $12.2-12.4$ GeV in both $[{\bar{3}}_{\mathbf{c}}{]}_{bc}\otimes [3_{\mathbf{c}}{]}_{\bar{b}\bar{c}}$ and $[6_{\mathbf{c}}{]}_{bc}\otimes [{\bar{6}}_{\mathbf{c}}{]}_{\bar{b}\bar{c}}$ color configuration channels. Except for two $0^{++}$ states, such results are below the thresholds $T_{{\eta }_c{\eta }_b}/T_{{\rm Y}\psi }$ and $T_{B_c{B}_c}$, implying that these S-wave positive parity $bc\bar{b}\bar{c}$ tetraquark states are probably stable against the strong interaction. For the P-wave negative parity $bc\bar{b}\bar{c}$ tetraquarks, their masses in the $[{\bar{3}}_{\mathbf{c}}{]}_{bc}\otimes [3_{\mathbf{c}}{]}_{\bar{b}\bar{c}}$ channel are around $12.9-13.2$ GeV, while a bit higher in the $[6_{\mathbf{c}}{]}_{bc}\otimes [{\bar{6}}_{\mathbf{c}}{]}_{\bar{b}\bar{c}}$ channel. They can decay into the $c\bar{c}+b\bar{b}$ and $c\bar{b}+b\bar{c}$ final states via the spontaneous dissociation mechanism, including the $J/\psi {\rm Y}$, ${\eta }_c{\rm Y}$, $J/\psi {\eta }_b$, $B_c^{+}{B}_c^{-}$ channels.

    hep-phhep-exPRD(2021)·28 citations
11. 11*

    Magneto-rotational dissociation of heavy hadrons in Relativistic Heavy-Ion Collisions

    Kirill Tuchin🇺🇸

    A heavy hadron traversing Quark-Gluon Plasma and dragged along in rotational motion is subject to the Lorentz and centrifugal forces. The Lorentz force, sourced by the valence quarks of heavy-ions, possesses the electric and magnetic components in the hadron comoving frame. The electric component renders the hadron unstable by empowering one of its quarks to tunnel through the potential barrier. Assuming that the magnetic field is parallel to the plasma vorticity, the hadron dissociation probability is computed using the Imaginary Time Method and is found to strongly depend on the sign of the quark electric charge. The dissociation probability monotonically increases as a function of vorticity for negative electric charges, whereas for positive charges it exhibits a minimum at a finite value of vorticity. The dissociation probability for the negative charges is larger than for the positive ones at the same magnetic field and vorticity. In relativistic heavy-ion collisions this implies lower abundance of the negatively charged hadrons as compared to the positively charges ones. This effect is significant at moderate collision energies where the plasma vorticity is comparable or larger than the synchrotron frequency.

    hep-phastro-ph.SRnucl-thPLB(2021)·7 citations
12. 12*

    On Quantum Anomalous Effects in Electrodynamics of the Early Universe

    Petar Pavlović🇩🇪

    This dissertation studies the quantum anomalous effects on the description of high energy electrodynamics. We argue that on the temperatures comparable to the electroweak scale, characteristic for the early Universe and objects like neutron stars, the description of electromagnetic fields in conductive plasmas needs to be extended to include the effects of chiral anomaly. It is demonstrated that chiral effects can have a significant influence on the evolution of magnetic fields, tending to produce exponential amplification, creation of magnetic helicity from initially non-helical fields, and can lead to an inverse energy transfer. We further discuss the modified magnetohydrodynamic equations around the electroweak transition. The obtained solutions demonstrate that the asymmetry between right-handed and left-handed charged fermions of negligible mass typically grows with time when approaching the electroweak crossover from higher temperatures, until it undergoes a fast decrease at the transition, and then eventually gets damped at lower temperatures in the broken phase. At the same time, the dissipation of magnetic fields gets slower due to the chiral effects. We furthermore report some first analytical attempts in the study of chiral magnetohydrodynamic turbulence. Using the analysis of simplified regimes and qualitative arguments, it is shown that anomalous effects can strongly support turbulent inverse cascade and lead to a faster growth of the correlation length, when compared to the evolution predicted by the non-chiral magnetohydrodynamics. Finally, the discussion of relaxation towards minimal energy states in the chiral magnetohydrodynamic turbulence is also presented.

    hep-ph0 citations
13. 13*

    Neutrino Energy Loss Rates in 3-3-1 Models

    D.T.Binh🇻🇳 · L.T.Hue🇻🇳 · V. H. Binh🇻🇳 · H. N. Long🇻🇳

    The stellar energy-loss rates $\mathcal{Q}$ due to the production of neutrino pair in the framework of 3-3-1 models are presented. The energy loss rate $\mathcal{Q}$ is evaluated for different values of $\beta =\pm \text{fr}1\sqrt{3},\pm \text{fr}2\sqrt{3},\pm \sqrt{3}$ in which $\beta$ is a parameter used to define the charge operator in the 3-3-1 models. The correction to the rate which is compared with that of the Standard Model ($\text{de}\mathcal{Q}$) is also evaluated. We show that the correction does not exceed 14\% and %is gets the highest with $\beta =-\sqrt{3}$. The contribution of dipole moment to the energy loss rate is small compared to the contribution of new natural gauge boson $Z^{\prime }$ and this sets constraints for the mass of Z' $m_{Z^{\prime }}\le 4000$ GeV. This mass range is within the searching range for $Z^{\prime }$ boson at LHC.

    hep-phInt.J.Mod.Phys.A(2021)·2 citations
14. 14*

    Forces inside the nucleon on the light front from 3D Breit frame force distributions: Abel tomography case

    Julia Yu. Panteleeva🇩🇪 · Maxim V. Polyakov🇩🇪

    We derive simple relations which express 2D light front force distributions in terms of 3D Breit frame pressure and shear force distributions. Mathematically the relations correspond to invertible Abel transformation and they establish one-to-one mathematical equivalence of 3D Breit frame force distributions and 2D light front ones. Any knowledge (model calculation, experimental measurement, etc.) about pressure and shear force distributions in Breit frame can be unambiguously transformed into light front force distributions with the help of Abel transformation. It is important that the transformation ensures 2D stability conditions if the 3D stability conditions are satisfied. As an illustration of how the relations work, we calculated the light front force distributions for a large nucleus as a liquid drop, and for large $N_c$ nucleon as a chiral soliton.

    hep-phhep-exnucl-exnucl-thPRD(2021)·63 citations
15. 15*

    Radiative dark matter and neutrino masses from an alternative $U(1{)}_{B-L}$ gauge symmetry

    Hiroshi Okada🇰🇷 · Yuta Orikasa🇨🇿 · Yutaro Shoji🇮🇱

    We propose a model where the masses of the active neutrinos and a dark matter candidate are generated radiatively through the $U(1{)}_{B-L}$ gauge symmetry breaking. It is realized by a non-universal $U(1{)}_{B-L}$ charge assignment on the right handed neutrinos and one of them becomes DM. The dark matter mass becomes generally small compared with the typical mass of the Weak Interacting Massive Particles and we have milder constraints on the dark matter. We consider the case where the dark matter is produced through the freeze-in mechanism and show that the observed dark matter relic density can be realized consistently with the current experimental constraints on the neutrino masses and the lepton flavor structure.

    hep-phJCAP(2021)·9 citations
16. 16*

    Thermal properties of light mesons from holography

    Xuanmin Cao🇨🇳 · Songyu Qiu🇨🇳 · Hui Liu🇨🇳 · Danning Li🇨🇳

    The thermal properties of light mesons, including the temperature dependence of their masses (both screening and pole masses) and thermal widths, are studied in a two-flavor ($N_f=2$) soft-wall AdS/QCD model. By solving the spatial correlation functions, we extract the screening masses ($m_{\mathrm{scr}}$) from their poles. The screening masses of pseudo-scalar ($\pi$) and axial-vector ($a_1$) mesons increase almost monotonously with the increase of temperature. The screening masses of scalar ($\sigma$) and vector ($\rho$) mesons decrease at low temperature and increase at high temperature. The pole masses ($m_{\mathrm{pole}}$) and the thermal widths ($\Gamma$) are extracted from the temporal correlation functions and the corresponding spectral functions. The results indicate that the pole masses have local minima at low temperature and increase at high temperature. The thermal widths increase rapidly above the chiral crossover temperature $T_{cp}$, indicating the dissociations of mesons at high temperature. Furthermore, the degeneration of the chiral partners ($\pi$ and $\sigma$, $\rho$ and $a_1$) above $T_{cp}$ is observed from the screening and pole masses, revealing the chiral symmetry restoration at the hadronic spectrum level. Finally, we numerically verify that the spectral functions in the temporal regime are strongly related to the quasi-normal modes with complex frequencies ${\omega }_0=m_{\mathrm{pole}}-i\Gamma /2$.

    hep-phhep-thJHEP(2021)·28 citations
17. 17*

    Vector-Boson Scattering at the LHC: unravelling the Electroweak sector

    Roberto Covarelli🇮🇹 · Mathieu Pellen🇩🇪 · Marco Zaro🇮🇹

    Vector-boson scattering (VBS) processes probe the innermost structure of electroweak interactions in the Standard Model, and provide a unique sensitivity for new physics phenomena affecting the gauge sector. In this review, we report on the salient aspects of this class of processes, both from the theory and experimental point of view. We start by discussing recent achievements relevant for their theoretical description, some of which have set important milestones in improving the precision and accuracy of the corresponding simulations. We continue by covering the development of experimental techniques aimed at detecting these rare processes and improving the signal sensitivity over large backgrounds. We then summarise the details of the most relevant VBS signatures and review the related measurements available to date, along with their comparison with Standard-Model predictions. We conclude by discussing the perspective at the upcoming Large Hadron Collider runs and at future hadron facilities.

    hep-phhep-exInt.J.Mod.Phys.A(2021)·67 citations
18. 18*

    The ground states and the first radially excited states of D-wave vector $\rho$ and $\varphi$ mesons

    Guo-Liang Yu🇨🇳 · Zhi-Gang Wang🇨🇳 · Xiu-Wu Wang🇨🇳 · Hui-Juan Wang🇨🇳

    In this article, we firstly derive two QCD sum rules QCDSR I and QCDSR II which are respectively used to extract observable quantities of the ground states and the first radially excited states of D-wave vector $\rho$ and $\varphi$ mesons. In our calculations, we consider the contributions of vacuum condensates up to dimension-7 in the operator product expansion. The predicted masses for $1^3{D}_1$ $\rho$ meson and $2^3{D}_1$ $\varphi$ meson are consistent well with the experimental data of $\rho$($1700$) and $\varphi$($2170$). Besides, our analysis indicates that it is reliable to assign the recent reported $Y$($2040$) state as the $2^3{D}_1$ $\rho$ meson. Finally, we obtain the decay constants of these states with QCDSR I and QCDSR II. These predictions are helpful not only to reveal the structure of the newly observed $Y$($2040$) state but also to establish $\varphi$ meson and $\rho$ meson families.

    hep-phInt.J.Mod.Phys.A(2021)·7 citations
19. 19*

    On long-range pionic Bose-Einstein correlations -- Including analyses of OPAL, L3 and CMS BECs

    Takuya Mizoguchi🇯🇵 · Minoru Biyajima🇯🇵

    Long-range correlation plays an important role in analyses of pionic Bose-Einstein correlations (BECs). In many cases, such correlations are phenomenologically introduced. In this investigation, we propose an analytic form. By making use of the form, we analyze the OPAL BEC and the L3 BEC at $Z^0$-pole and the CMS BEC at 0.9 and 7 TeV using our formulas and the $\tau$-model. The parameters estimated by both approaches are found to be consistent. Utilizing the Fourier transform in four-dimensional Euclidean space, a number of pion-pair density distributions are also studied.

    hep-phhep-exnucl-th1 citation
20. 20*

    Robust approach to thermal resummation: Standard Model meets a singlet

    Philipp M. Schicho🇫🇮 · Tuomas V. I. Tenkanen🇸🇪 · Juuso Österman🇫🇮

    Perturbation theory alone fails to describe thermodynamics of the electroweak phase transition. We review a technique combining perturbative and non-perturbative methods to overcome this challenge. Accordingly, the principal theme is a tutorial of high-temperature dimensional reduction. We present an explicit derivation with a real singlet scalar and compute the thermal effective potential at two-loop order. In particular, we detail the dimensional reduction for a real-singlet extended Standard Model. The resulting effective theory will impact future non-perturbative studies based on lattice simulations as well as purely perturbative investigations.

    hep-phastro-ph.COgr-qchep-thJHEP(2021)·99 citations
21. 21*

    Exploring dark sector parameters in light of neutron star temperatures

    Guey-Lin Lin🇹🇼 · Yen-Hsun Lin🇹🇼

    Using neutron stars (NS) as a dark matter (DM) probe has gained broad attention recently, either from heating due to DM annihilation or its stability under the presence of DM. In this work, we investigate spin-$1/2$ fermionic DM $\chi$ charged under the $U(1{)}_X$ in the dark sector. The massive gauge boson $V$ of $U(1{)}_X$ gauge group can be produced in NS via DM annihilation. The produced gauge boson can decay into Standard Model (SM) particles before it exits the NS, despite its tiny couplings to SM particles. Thus, we perform a systematic study on $\chi \bar{\chi }\to 2V\to 4\mathrm{SM}$ as a new heating mechanism for NS in addition to $\chi \bar{\chi }\to 2\mathrm{SM}$ and kinetic heating from DM-baryon scattering. The self-trapping due to $\chi V$ scattering is also considered. We assume the general framework that both kinetic and mass mixing terms between $V$ and SM gauge bosons are present. This allows both vector and axial-vector couplings between $V$ and SM fermions even for $m_V\ll m_Z$. Notably, the contribution from axial-vector coupling is not negligible when particles scatter relativistically. We point out that the above approaches to DM-induced NS heating are not yet adopted in recent analyses. Detectabilities of the aforementioned effects to the NS surface temperature by the future telescopes are discussed as well.

    hep-phastro-ph.HEPRD(2021)·8 citations
22. 22*

    Gauge Fields as Constrained Composite Bosons

    J.L. Chkareuli🇬🇪

    We reconsider a scenario in which photons and other gauge fields appear as the composite vector bosons made of the fermion pairs that may happen with or without spontaneous violation of Lorentz invariance. The class of composite models for emergent gauge fields is proposed, where these fields are required to be restricted by by the nonlinear covariant constraint of type $A_{\mu }^2=M^2$. Such a constraint may only appear if the corresponding fermion currents in the prototype model, being invariant under some global internal symmetry $G$, are properly constrained as well. In contrast to the conventional approach, the composite bosons emerged in this way appear naturally massless, the global symmetry $G$ in the model turns into the local symmetry $G_{loc}$, while the vector field constraint reveals itself as the gauge fixing condition. Finally, we consider the case when the constituent fermions generating emergent gauge bosons could be at the same time the preons composing the known quark-lepton species in the Standard Model and Grand Unified Theories.

    hep-phhep-thPLB(2021)·4 citations
23. 23*

    On Broad Kaluza-Klein Gluons

    Rafel Escribano🇪🇸 · Mikel Mendizabal🇩🇪 · Mariano Quirós🇪🇸 · Emilio Royo🇪🇸

    In theories with a warped extra dimension, composite fermions, as e.g. the right-handed top quark, can be very strongly coupled to Kaluza-Klein (KK) fields. In particular, the KK gluons in the presence of such composite fields become very broad resonances, thus remarkably modifying their experimental signatures. We have computed the pole mass and the pole width of the KK gluon, triggered by its interaction with quarks, as well as the prediction for proton-proton cross-sections using the full propagator and compared it with that obtained from the usual Breit-Wigner approximation. We compare both approaches, along with the existing experimental data from ATLAS and CMS, for the $t\bar{t}$, $t\bar{t}W$, $t\bar{t}Z$, $t\bar{t}H$, and $t\bar{t}t\bar{t}$ channels. We have found differences between the two approaches of up to about 100%, highlighting that the effect of broad resonances can be dramatic on present, and mainly future, experimental searches. The channel $t\bar{t}t\bar{t}$ is particularly promising because the size of the cross-section signal is of the same order of magnitude as the Standard Model prediction, and future experimental analyses in this channel, especially for broad resonances, can shed light on the nature of possible physics beyond the Standard Model.

    hep-phhep-exhep-thJHEP(2021)·10 citations
24. 24*

    Axi-Higgs Cosmology

    Leo WH Fung🇨🇳 · Lingfeng Li🇨🇳 · Tao Liu🇨🇳 · Hoang Nhan Luu🇨🇳 · Yu-Cheng Qiu🇨🇳 · S.-H. Henry Tye🇨🇳

    If the electroweak Higgs vacuum expectation value $v$ in early universe is $\sim 1\%$ higher than its present value $v_0=246$ GeV, the ${}^7$Li puzzle in BBN and the CMB/$\Lambda$CDM tension with late-universe measurements on Hubble parameter are mitigated. We propose a model of an axion coupled to the Higgs field, named ``axi-Higgs'', with its mass $m_a\sim 10^{-30}-10^{-29}\mathrm{eV}$ and decay constant $f_a\sim 10^{17}-10^{18}\mathrm{GeV}$, to achieve this goal. The axion initial value $a_{\mathrm{ini}}$ yields an initial $\Delta v_{\mathrm{ini}}/v_0\sim 0.01$ throughout the BBN-recombination epoch and a percent level contribution to the total matter density today. Because of its very large de Broglie wavelength, this axion matter density ${\omega }_a$ suppresses the matter power spectrum, alleviating the CMB/$\Lambda$CDM $S_8/{\sigma }_8$ tension with the weak-lensing data. It also explains the recently reported isotropic cosmic birefringence by its coupling with photons. Adding the axion ($m\sim 10^{-22}$eV) in the fuzzy dark matter model to the axi-Higgs model allows bigger $\Delta v_{\mathrm{rec}}$ and ${\omega }_a$ to address the Hubble and $S_8/{\sigma }_8$ tensions simultaneously. The model predicts that $\Delta v$ may be detected by the spectral measurements of quasars, while its oscillation may be observed in the atomic clock measurements.

    hep-phastro-ph.COhep-thJCAP(2021)·46 citations
25. 25*

    Analytical spectrum of nonlinear Thomson scattering including radiation reaction

    A. Di Piazza🇩🇪 · G. Audagnotto🇩🇪

    Accelerated charges emit electromagnetic radiation and the consequent energy-momentum loss alters their trajectory. This phenomenon is known as radiation reaction and the Landau-Lifshitz (LL) equation is the classical equation of motion of the electron, which takes into account radiation-reaction effects in the electron trajectory. By using the analytical solution of the LL equation in an arbitrary plane wave, we compute the analytical expression of the classical emission spectrum via nonlinear Thomson scattering including radiation-reaction effects. Both the angularly-resolved and the angularly-integrated spectra are reported, which are valid in an arbitrary plane wave. Also, we have obtained a phase-dependent expression of the electron dressed mass, which includes radiation-reaction effects. Finally, the corresponding spectra within the locally constant field approximation have been derived.

    hep-phPRD(2021)·14 citations
26. 26*

    Electromagnetic Signatures of Dark Photon Superradiance

    Andrea Caputo🇮🇱 · Samuel J. Witte🇳🇱 · Diego Blas🇬🇧 · Paolo Pani🇮🇹

    Black hole superradiance is a powerful tool in the search for ultra-light bosons. Constraints on the existence of such particles have been derived from the observation of highly spinning black holes, absence of continuous gravitational-wave signals, and of the associated stochastic background. However, these constraints are only strictly speaking valid in the limit where the boson's interactions can be neglected. In this work we investigate the extent to which the superradiant growth of an ultra-light dark photon can be quenched via scattering processes with ambient electrons. For dark photon masses $m_{{\gamma }^{\prime }}\gtrsim 10^{-17}\mathrm{eV}$, and for reasonable values of the ambient electron number density, we find superradiance can be quenched prior to extracting a significant fraction of the black-hole spin. For sufficiently large $m_{{\gamma }^{\prime }}$ and small electron number densities, the in-medium suppression of the kinetic mixing can be efficiently removed, and quenching occurs for mixings ${\chi }_0\gtrsim \mathcal{O}(10^{-8})$; at low masses, however, in-medium effects strongly inhibit otherwise efficient scattering processes from dissipating energy. Intriguingly, this quenching leads to a time- and energy-oscillating electromagnetic signature, with luminosities potentially extending up to $\sim 10^{57}erg/s$, suggesting that such events should be detectable with existing telescopes. As a byproduct we also show that superradiance cannot be used to constrain a small mass for the Standard Model photon.

    hep-phastro-ph.COgr-qchep-thPRD(2021)·62 citations
27. 27*

    Signatures of toponium formation in LHC run 2 data

    Benjamin Fuks🇫🇷 · Kaoru Hagiwara🇯🇵 · Kai Ma🇨🇳 · Ya-Juan Zheng🇺🇸

    We study reported deviations between observations and theoretical predictions associated with the production of a pair of di-leptonically decaying top quarks at the LHC, and we examine the possibility that they reflect a signal of toponium formation. We investigate the production by gluon fusion of a color-singlet spin-0 toponium ${\eta }_t$ bound state of a top and anti-top quark, that then decays di-leptonically ($gg\to {\eta }_t\to \bar{\ell }\ell b\bar{b}\nu \bar{\nu }$). We find strong correlations favoring the production of di-lepton systems featuring a small angular separation in azimuth and a small invariant mass. Although toponium production only contributes to 0.8% of the total top-quark pair-production cross section at the 13 TeV LHC, there is a possibility that it can account for observed excesses in the narrow edges of phase space. We propose a method to discover toponium formation by `reconstructing' both its top and anti-top quark constituents in the di-lepton channel.

    hep-phPRD(2021)·100 citations
28. 28*

    A composite solution to the EDGES anomaly

    Anubhav Mathur🇺🇸 · Surjeet Rajendran🇺🇸 · Harikrishnan Ramani🇺🇸

    Subcomponent millicharged dark matter that cools baryons via Coulomb interactions has been invoked to explain the EDGES anomaly. However, this model is in severe tension with constraints from cosmology and stellar emissions. In this work, we consider the consequences of these millicharged particles existing in composite blobs. The relevant degrees of freedom at high temperature are minuscule elementary charges, which fuse at low temperatures to make up blobs of larger charge. These blobs serve as the degrees of freedom relevant in cooling the baryons sufficiently to account for the EDGES anomaly. In such a model, cosmology and stellar constraints (which involve high-temperature processes) apply only to the feebly-interacting elementary charges and not to the blobs. This salvages a large range of parameter space for millicharged blobs that can explain the EDGES anomaly. It also opens up new parameter space for direct detection, albeit at low momentum transfers.

    hep-phastro-ph.COPRD(2022)·16 citations
29. 29*

    Hunting wino and higgsino dark matter at the muon collider with disappearing tracks

    Rodolfo Capdevilla🇨🇦 · Federico Meloni🇩🇪 · Rosa Simoniello🇨🇭 · Jose Zurita🇪🇸

    We study the capabilities of a muon collider experiment to detect disappearing tracks originating when a heavy and electrically charged long-lived particle decays via $X^{+}\to Y^{+}{Z}^0$, where $X^{+}$ and $Z^0$ are two almost mass degenerate new states and $Y^{+}$ is a charged Standard Model particle. The backgrounds induced by the in-flight decays of the muon beams (BIB) can create detector hit combinations that mimic long-lived particle signatures, making the search a daunting task. We design a simple strategy to tame the BIB, based on a detector-hit-level selection exploiting timing information and hit-to-hit correlations, followed by simple requirements on the quality of reconstructed tracks. Our strategy allows us to reduce the number of tracks from BIB to an average of 0.08 per event, hence being able to design a cut-and-count analysis that shows that it is possible to cover weak doublets and triplets with masses close to $\sqrt{s}/2$ in the 0.1-10 ns range. In particular, this implies that a 10 TeV muon collider is able to probe thermal MSSM higgsinos and thermal MSSM winos, thus rivaling the FCC-hh in that respect, and further enlarging the physics program of the muon collider into the territory of WIMP dark matter and long-lived signatures. We also provide parton-to-reconstructed level efficiency maps, allowing an estimation of the coverage of disappearing tracks at muon colliders for arbitrary models.

    hep-phJHEP(2021)·106 citations
30. 30*

    Regge theory in a Holographic dual of QCD in the Veneziano Limit

    Artur Amorim🇵🇹 · Miguel S. Costa🇵🇹 · Matti Järvinen🇰🇷

    We initiate the study of Regge theory in a bottom-up holographic model for QCD in the Veneziano limit, where the backreaction of the quarks to the gluon dynamics is included. We determine the parameters of the model by carrying out a precise fit to the meson spectrum in QCD. The spectrum for spin-one and pseudoscalar mesons is well reproduced. We then generalise the model to incluce higher spin fields in the bulk trajectories dual to the Pomeron and meson Regge trajectories at the boundary. With this setting, we fit the masses of the mesons with spins $J=2$, $3$, and $4$,as well as the experimental data of the total cross-sections $\sigma (\gamma \gamma \to X)$, $\sigma (\gamma p\to X)$ and $\sigma (pp\to X)$. For the cross sections we obtain a ${\chi }_{d.o.f.}^2$ of $0.74$ for a total of 199 experimental points.

    hep-phhep-thJHEP(2021)·27 citations
31. 31*

    Higher-order corrections for $tW$ production at high-energy hadron colliders

    Nikolaos Kidonakis🇺🇸 · Nodoka Yamanaka🇺🇸

    We discuss cross sections for $tW$ production in proton-proton collisions at the LHC and at higher-energy colliders with energies of up to 100 TeV. We find that, remarkably, the soft-gluon corrections are numerically dominant even at very high collider energies. We present results with soft-gluon corrections at approximate NNLO and approximate N${}^3$LO matched to complete NLO results. These higher-order corrections are large and need to be included for better theoretical accuracy and smaller scale dependence. Total cross sections as well as top-quark and $W$-boson transverse-momentum and rapidity distributions are presented using various recent sets of parton distribution functions.

    hep-phJHEP(2021)·134 citations
32. 32*

    Classical Lagrangians for the nonminimal spin-nondegenerate Standard-Model Extension at higher orders in Lorentz violation

    João A.A.S Reis🇧🇷 · Marco Schreck🇧🇷

    We present new results for classical-particle propagation subject to Lorentz violation. Our analysis is dedicated to spin-nondegenerate operators of arbitrary mass dimension provided by the fermion sector of the Standard-Model Extension. In particular, classical Lagrangians are obtained for the operators ${\hat{b}}_{\mu }$ and ${\hat{H}}_{\mu \nu }$ as perturbative expansions in Lorentz violation. The functional dependence of the higher-order contributions in the background fields is found to be quite peculiar, which is probably attributed to particle spin playing an essential role for these cases. This paper closes one of the last gaps in understanding classical-particle propagation in the presence of Lorentz violation. Lagrangians of the kind presented will turn out to be valuable for describing particle propagation in curved backgrounds with diffeomorphism invariance and/or local Lorentz symmetry explicitly violated.

    ↳ hep-thhep-phPRD(2021)·14 citations
33. 33*

    Proper-time method for unequal masses

    A.A. Osipov🇷🇺

    The result of removing of heavy non-equal mass particles from the theory can be described, at low energy, by the effective action, which is a series in inverse-square powers of the mass. We propose a new efficient tool to calculate the leading terms of this series based on the Schwinger proper-time method. Unequal masses give rise to a large number of effective vertices describing the explicit flavour symmetry breaking effects with well-defined coupling constants. Our method is pertinent to the theory with explicit and spontaneous chiral symmetry breaking, chiral gauge theory, standard and beyond standard model effective field theory, the theory of critical phenomena, cosmology, etc.

    ↳ hep-thhep-phPLB(2021)·14 citations
34. 34*

    Connecting multi-lepton anomalies at the LHC and in Astrophysics with MeerKAT/SKA

    Geoff Beck🇿🇦 · Ralekete Temo🇿🇦 · Elias Malwa🇿🇦 · Mukesh Kumar🇿🇦 · Bruce Mellado🇿🇦

    Multi-lepton anomalies at the Large Hadron Collider (LHC) are reasonably well described by a two Higgs doublet model with an additional singlet scalar. Here, we demonstrate that using this model with parameters set by the LHC, we are also able to describe the excesses in gamma-ray flux from the galactic centre and the cosmic-ray spectra from AMS-02. This is achieved through Dark Matter (DM) annihilation via the singlet scalar. Of great interest is the flux of synchrotron emissions which results from annihilation of DM in Milky-Way satellites. We make predictions for MeerKAT/SKA observations of the nearby dwarf galaxy Reticulum II and we demonstrate the power of this instrument as a new frontier in indirect dark matter searches. Since the dark matter sector of the aforementioned two Higgs doublet model is unconstrained by current LHC data, we also demonstrate a synergy between particle and astrophysical searches in order to motivate further exploration of this promising model.

    ↳ astro-ph.HEastro-ph.IMhep-exhep-phAstropart.Phys.(2023)·18 citations
35. 35*

    Background Field Method and Generalized Field Redefinitions in Effective Field Theories

    Andrea Quadri (INFN, Sez. di Milano)🇮🇹

    We show that in a spontaneously broken effective gauge field theory, quantized in a general background $R_{\xi }$-gauge, also the background fields undergo a non-linear (albeit background-gauge invariant) field redefinition induced by radiative corrections. This redefinition proves to be crucial in order to renormalize the coupling constants of gauge-invariant operators in a gauge-independent way. The classical background-quantum splitting is also in general non-linearly deformed (in a non gauge-invariant way) by radiative corrections. Remarkably, such deformations vanish in the Landau gauge, to all orders in the loop expansion.

    ↳ hep-thhep-phEur.Phys.J.Plus(2021)·3 citations
36. 36*

    Strongly Coupled String-inspired Infinite Derivative Non-local Yang-Mills: Diluted Mass Gap

    Marco Frasca🇮🇹 · Anish Ghoshal🇮🇹

    We investigate the non-perturbative regimes in the class of non-Abelian theories that have been proposed as an ultraviolet completion 4-D Quantum Field Theory (QFT) generalizing the kinetic energy operators to an infinite series of higher-order derivatives inspired by string field theory. We prove that, at the non-perturbative level, the physical spectrum of the theory is actually corrected by the 'infinite number of derivatives' present in the action. We derive a set of Dyson-Schwinger equations in differential form, for correlation functions till two-points, the solution for which are known in the local theory. We obtain that just like in the local theory, the non-local counterpart displays a mass gap, depending also on the mass scale of non-locality, and show that it is damped in the deep UV reaching asymptotically the conformal limit. We point out some possible implications of our result in particle physics and cosmology and discuss aspects of non-local QCD-like scenarios. We end with some comments on the infinite-derivative non-local gravity which is quantum gravity approach to ghost-free, re-normalizable theories of gravity valid upto infinte ebergy scales in the UV.

    ↳ hep-thhep-phJHEP(2020)·16 citations
37. 37*

    Confinement-Deconfinement transition and $Z_2$ symmetry in $Z_2+$Higgs theory

    Minati Biswal🇮🇳 · Sanatan Digal🇮🇳 · Vinod Mamale🇮🇳 · Sabiar Shaikh🇮🇳

    We study the Polyakov loop and the $Z_2$ symmetry in the lattice $Z_2+$Higgs theory in 4D Euclidean space using Monte Carlo simulations. The results show that this symmetry is realised in the Higgs symmetric phase for large number of temporal lattice sites. To understand the dependence on the number of temporal sites, we consider a one dimensional model by keeping terms of the original action corresponding to a single spatial site. In this approximation the partition function can be calculated exactly as a function of the Polyakov loop. The resulting free energy is found to have the $Z_2$ symmetry in the limit of large temporal sites. We argue that this is due to $Z_2$ invariance as well as dominance of the distribution or density of states corresponding to the action.

    ↳ hep-lathep-phnucl-thMod.Phys.Lett.A(2021)·3 citations
38. 38*

    Conserved and non-conserved Noether currents from the quantum effective action

    Stefan Floerchinger🇩🇪 · Eduardo Grossi🇺🇸

    The quantum effective action yields equations of motion and correlation functions including all quantum corrections. We discuss here how it encodes also Noether currents at the full quantum level. Interestingly, the construction can be generalized beyond the standard symmetry transformations that leave the action invariant. We also discuss an extended set of transformations, which change the action by a term that is locally known on the level of the quantum effective action. Associated to such extended gauge transformations are currents for which we obtain a divergence-type equation of motion, but they are not conserved. We call them non-conserved Noether currents. We discuss in particular symmetries and extended transformations associated to space-time geometry for relativistic quantum field theories. These encompass local dilatations or Weyl gauge transformation, local Lorentz transformations and local shear transformations. Together they constitute the symmetry group of the frame bundle GL$(d)$. The corresponding non-conserved Noether currents are the dilatation or Weyl current, the spin current and the shear current. In particular for the latter we obtain a new divergence-type equations of motion.

    ↳ hep-thgr-qchep-phnucl-thPRD(2022)·15 citations
39. 39*

    $\gamma \gamma$ decay as a probe of neutrinoless $\beta \beta$ decay nuclear matrix elements

    B. Romeo🇪🇸 · J. Menéndez🇪🇸 · C. Peña🇪🇸

    We study double gamma ($\gamma \gamma$) decay nuclear matrix elements (NMEs) for a wide range of nuclei from titanium to xenon, and explore their relation to neutrinoless double-beta ($0\nu \beta \beta$) NMEs. To favor the comparison, we focus on double-magnetic dipole transitions in the final $\beta \beta$ nuclei, in particular the $\gamma \gamma$ decay of the double isobaric analog of the initial $\beta \beta$ state into the ground state. For the decay with equal-energy photons, our large-scale nuclear shell model results show a good linear correlation between the $\gamma \gamma$ and $0\nu \beta \beta$ NMEs. Our analysis reveals that the correlation holds for $\gamma \gamma$ transitions driven by the spin or orbital angular momentum due to the dominance of zero-coupled nucleon pairs, a feature common to $0\nu \beta \beta$ decay. Our shell-model findings point out the potential of future $\gamma \gamma$ decay measurements to constrain $0\nu \beta \beta$ NMEs, which are key to answer fundamental physics questions based on $0\nu \beta \beta$ experiments.

    ↳ nucl-thhep-exhep-phnucl-exPLB(2022)·29 citations
40. 40*

    Nonuniform-temperature effects on the phase transition in an Ising-like model

    Jun-Hui Zheng🇳🇴 · Lijia Jiang🇨🇳

    In this study, we investigate the spatially nonuniform-temperature effects on the QCD chiral phase transition in the heavy-ion collisions. Since the QCD effective theory and the Ising model belong to the same universality class, we start our discussion by mimicking the QCD effective potential with an Ising-like effective potential. In contrast to the dynamical slowing down effects which delays the phase transition from quark-gluon-plasma to hadron gas, the spatially nonuniform-temperature effects show a possibility to lift the phase transition temperature. Besides, both the fluctuations and the correlation length are enhanced in the phase transition region. Furthermore, the critical phenomena is strongly suppressed like as the critical slowing down effects. The underlying mechanism is the nonzero-momentum mode fluctuations of the order parameter induced by the nonuniform temperature. Our study provides a method to evaluate the nonuniform-temperature effects, and illustrate its potential influence on analyzing the QCD phase transition signals at RHIC.

    ↳ nucl-thhep-phPRD(2021)·4 citations
41. 41*

    The smallest fluid on earth

    Björn Schenke🇺🇸

    High energy heavy ion collisions create quark gluon plasmas that behave like almost perfect fluids. Very similar features to those that led to this insight have also been observed in experimental data from collisions of small systems, involving protons or other light nuclei. We describe recent developments aimed at understanding whether, and if so how, systems that produce relatively few particles (orders of magnitude less than in typical heavy ion collisions) and are only one to a few times the size of a proton, can behave like fluids. This involves a deeper understanding of fluid dynamics and its applicability, improvements of our understanding of the initial geometry of the collisions by considering fluctuations of the proton shape, as well as advancements in the calculation of initial state effects within an effective theory of quantum chromodynamics, which can affect the observables that are used to study fluid behavior. We further address open questions and discuss future directions.

    ↳ nucl-thhep-phnucl-exRept.Prog.Phys.(2021)·108 citations
42. 42*

    Search for Lorentz Invariance Violation from stacked Gamma-Ray Burst spectral lag data

    Rajdeep Agrawal🇮🇳 · Haveesh Singirikonda🇮🇳 · Shantanu Desai🇮🇳

    A number of works have claimed detections of a turn-over in the spectral lag data for individual Gamma-Ray Bursts (GRBs), caused by an energy-dependent speed of light, which could be a possible manifestation of Lorentz invariance violation (LIV). Here, we stack the spectral lag data from a total of 37 GRBs (with a total of 91 measurements), to verify if the combined data is consistent with a unified model consisting of intrinsic astrophysical emission, along with another contribution due to LIV. We then carry out Bayesian model comparison to ascertain if this combined spectral lag data shows a preference for an energy-dependent speed of light, as compared to only an intrinsic astrophysical emission mechanism. We do not find a decisive evidence for such an energy-dependent speed of light for two different models of LIV. When we assume a constant intrinsic lag coupled with an unknown intrinsic scatter, we do not find any evidence for LIV. However, when we use GRB-dependent parameters to model the intrinsic emission, we get decisive evidence for LIV violation. We then carry out a search for LIV Standard Model Extension using this dataset as well as an independent search using a separate dataset consisting of rest-frame spectral lags. Finally, none of the models considered here with any of the aforementioned assumptions provide a good fit to the stacked spectral lag data, indicating that there is still missing Physics in the model for intrinsic spectral lags.

    ↳ astro-ph.HEastro-ph.COhep-phJCAP(2021)·28 citations
43. 43*

    Metaplectic Flavor Symmetries from Magnetized Tori

    Yahya Almumin🇺🇸 · Mu-Chun Chen🇺🇸 · Victor Knapp-Perez🇲🇽 · Saul Ramos-Sanchez🇲🇽 · Michael Ratz🇺🇸 · Shreya Shukla🇺🇸

    We revisit the flavor symmetries arising from compactifications on tori with magnetic background fluxes. Using Euler's Theorem, we derive closed form analytic expressions for the Yukawa couplings that are valid for arbitrary flux parameters. We discuss the modular transformations for even and odd units of magnetic flux, M, and show that they give rise to finite metaplectic groups the order of which is determined by the least common multiple of the number of zero-mode flavors involved. Unlike in models in which modular flavor symmetries are postulated, in this approach they derive from an underlying torus. This allows us to retain control over parameters, such as those governing the kinetic terms, that are free in the bottom-up approach, thus leading to an increased predictivity. In addition, the geometric picture allows us to understand the relative suppression of Yukawa couplings from their localization properties in the compact space. We also comment on the role supersymmetry plays in these constructions, and outline a path towards non-supersymmetric models with modular flavor symmetries.

    ↳ hep-thhep-phmath-phmath.MPJHEP(2021)·98 citations
44. 44*

    Ultrarelativistic electrons in counterpropagating laser beams

    Q. Z. Lv🇩🇪 · E. Raicher🇩🇪 · C. H. Keitel🇩🇪 · K. Z. Hatsagortsyan🇩🇪

    The dynamics and radiation of ultrarelativistic electrons in strong counterpropagating laser beams are investigated. Assuming that the particle energy is the dominant scale in the problem, an approximate solution of classical equations of motion is derived and the characteristic features of the motion are examined. A specific regime is found with comparable strong field quantum parameters of the beams, when the electron trajectory exhibits ultrashort spike-like features, which bears great significance to the corresponding radiation properties. An analytical expression for the spectral distribution of spontaneous radiation is derived in the framework of the Baier-Katkov semiclassical approximation based on the classical trajectory. All the analytical results are further validated by exact numerical calculations. We consider a non-resonant regime of interaction, when the laser frequencies in the electron rest frame are far from each other, avoiding stimulated emission. Special attention is devoted to settings when the description of radiation via the local constant field approximation fails and to corresponding spectral features. Periodic and non-periodic regimes are considered, when lab frequencies of the laser waves are always commensurate. The sensitivity of spectra with respect to the electron beam spread, focusing and finite duration of the laser beams is explored.

    ↳ physics.plasm-phhep-phNew J.Phys.(2021)·7 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.