Wed·Nov 27, 2019Wednesday·November 27, 2019

1. 01*

   $\Delta (1232)$ Contribution in the $\pi$-photoproduction on Nucleons in Covariant Chiral Perturbation Theory

   Gustavo H. Guerrero Navarro🇪🇸

   We study the effects of the $\Delta$(1232) resonance as an effective degree of freedom for charged and neutral pion photo-production on nucleons. Different observables have been calculated for these processes by using relativistic chiral perturbation theory up to $\mathcal{O}(p^3)$ in the $\delta$ counting, thus, including pion loops. We compare our model with a large database containing the available experimental data and constrain some unknown low energy constants.

   hep-ph0 citations
2. 02*

   The Time Substructure of Jets and Boosted Object Tagging

   Matthew D. Klimek🇺🇸

   We initiate the study of the time substructure of jets, motivated by the fact that the next generation of detectors at particle colliders will resolve the time scale over which jet constituents arrive. This effect is directly related to hadronization, which transforms partons into massive hadrons with a distribution of velocities. We review the basic predictions for the velocity distribution of jet hadrons, and suggest an application for this information in the context of boosted object tagging. By noting that the velocity distribution is determined by the properties of the color string which ends on the parton that initiates the jet, we observe that jets originating from boosted color singlets, such as Standard Model electroweak bosons, will exhibit velocity distributions that are boosted relative to QCD jets of similar jet energy. We find that by performing a simple cut on the corresponding distribution of charged hadron arrival times at the detector, we can discriminate against QCD jets that would otherwise give a false positive under a traditional spatial substructure based boosted object tagger.

   hep-phhep-exJ.Phys.G(2022)·4 citations
3. 03*

   Electroweak Loops as a Probe of New Physics in $t\bar{t}$ Production at the LHC

   Till Martini🇩🇪 · Markus Schulze🇩🇪

   We calculate the $\mathcal{O}(\alpha )$ weak corrections to top quark pair production at the LHC and include anomalous electroweak interactions from dimension-six operators. The loop calculation and renormalization are consistently done within the Standard Model Effective Field Theory. Sensitivity to the involved operators is exposed through the virtual corrections, which receive enhancement from electroweak Sudakov logarithms. We investigate the prospects of using this feature for probing New Physics at the LHC that so far has only been studied in final states with on-shell sensitivity such as $t\bar{t}+Z$ or $t\to bW$. We find that the large $t\bar{t}$ production rate and the excellent perturbative control allow compensating the loop suppression and yield remarkably strong constraints that are competitive with those from $t\bar{t}+Z$.

   hep-phhep-exJHEP(2020)·12 citations
4. 04*

   Dark Matter Freeze Out with Tsallis Statistics in the Early Universe

   Thomas D. Rueter🇺🇸 · Thomas G. Rizzo🇺🇸 · JoAnne L. Hewett🇺🇸

   The nature of dark matter (DM) and how it might interact with the particles of the Standard Model (SM) is one of greatest mysteries currently facing particle physics, and addressing these issues should provide some understanding of how the observed relic abundance was produced. One widely considered production mechanism, a weakly interacting massive particle (WIMP) produced as a thermal relic, provides a target cross section for DM annihilation into SM particles by solving the Boltzmann equation. In this thermal freeze-out mechanism, dark matter is produced in thermal equilibrium with the SM in the early universe, and drops out of equilibrium to its observed abundance as the universe cools and expands. In this paper, we study the impact of a generalized thermodynamics, known as Tsallis statistics and governed by a parameter $q$, on the target DM annihilation cross section. We derive the phase space distributions of particles in this generalized statistical framework, and check their thermodynamic consistency, as well as analyzing the impact of this generalization on the collisional term of the Boltzmann equation. We consider the case of an initial value of $q_0>1$, with $q$ relaxing to 1 as the universe expands and cools, and solve the generalized Boltzmann numerically for several benchmark DM masses, finding the corresponding target annihilation cross sections as a function of $q_0$. We find that as $q$ departs from the standard thermodynamic case of $q=1$, the collisional term falls less slowly as a function of $x=m_{\chi }/T$ than expected in the standard case. We also find that the target cross section falls sharply from $\sigma v\simeq 2.2-2.6\times 10^{-26}{\text{cm}}^3/\text{s}$ for $q_0=1$ to, for example, $\sigma v\simeq 3\times 10^{-34}{\text{cm}}^3/\text{s}$ for $q_0=1.05$ for a 100 GeV WIMP.

   hep-ph4 citations
5. 05*

   Extending the reach of FASER, MATHUSLA, and SHiP towards smaller lifetimes using secondary particle production

   Krzysztof Jodłowski🇵🇱 · Felix Kling🇺🇸 · Leszek Roszkowski🇵🇱 · Sebastian Trojanowski🇬🇧

   Many existing or proposed intensity-frontier search experiments look for decay signatures of light long-lived particles (LLPs), highly displaced from the interaction point, in a distant detector that is well-shielded from SM background. This approach is, however, limited to new particles with decay lengths similar to or larger than the baseline of those experiments. In this study, we discuss how this basic constraint can be overcome in BSM models that go beyond the simplest scenarios. If more than one light new particle is present in the model, an additional secondary production of LLPs may take place right in front of the detector, opening this way a new lifetime regime to be probed. We illustrate the prospects of such searches in the future experiments FASER, MATHUSLA and SHiP, for representative models, emphasizing possible connections to dark matter or an anomalous magnetic moment of muon. We also analyze additional advantages from employing dedicated neutrino detectors placed in front of the main decay volume.

   hep-phPRD(2020)·61 citations
6. 06*

   The effect of radiation corrections to the mass of an electron and positron on the polarization operator of a photon in a magnetic field

   V.M. Katkov🇷🇺

   The polarization operator of a photon in a constant and uniform magnetic field is studied taking into account the radiation width and shift of the Landau levels in both weak and strong fields compared with the critical field $H_0=4,41\cdot 10^{13}$ G . A general formula is obtained for the polarization operator of a photon in which radiation effects are taken into account. Now diverging previously threshold terms have a finite value. The conditions are formulated under which the energy levels completely overlap, and thereby the most appropriate application of the semiclassical operator method to the problem under study becomes.

   hep-ph0 citations
7. 07*

   The decay $\tau \to K^{\ast -}(892)\eta {\nu }_{\tau }$ in the NJL model

   M. K. Volkov🇷🇺 · A. A. Pivovarov🇷🇺 · K. Nurlan🇷🇺

   The decay width $\tau \to K^{\ast -}(892)\eta {\nu }_{\tau }$ was calculated in the Nambu--Jona-Lasinio model. Four channels were taken into account: the contact channel (the final states are directly producted from lepton current without any intermediate meson states), the axial-vector channel with two intermediate physical states $K_1(1270)$ and $K_1(1400)$, the vector channel with intermediate $K^{\ast }(892)$ meson and the pseudoscalar channel with intermediate $K$ meson. It is shown that the first two channels give the dominant contribution to the decay width. Of the remaining two channels, the pseudoscalar channel plays a more prominent role. The final result is in satisfactory agreement with experimental data. Prediction for the differential decay width is presented.

   hep-phNPA(2020)·8 citations
8. 08*

   Threshold effects in SO(10) models with one intermediate breaking scale

   Davide Meloni🇮🇹 · Tommy Ohlsson🇸🇪 · Marcus Pernow🇸🇪

   Despite the successes of the Standard Model of particle physics, it is known to suffer from a number of deficiencies. Several of these can be addressed within non-supersymmetric theories of grand unification based on $\mathrm{SO}(10)$. However, achieving gauge coupling unification in such theories is known to require additional physics below the unification scale, such as symmetry breaking in multiple steps. Many such models are disfavored due to bounds on the proton lifetime. Corrections arising from threshold effects can, however, modify these conclusions. We analyze all seven relevant breaking chains with one intermediate symmetry breaking scale, assuming the "survival hypothesis" for the scalar masses. Two are allowed by proton lifetime and two are disfavored by a failure to unify the gauge couplings. The remaining three unify at a too low scale, but can be salvaged by various amounts of threshold corrections. We parametrize this and thereby rank the models by the size of the threshold corrections required to save them.

   hep-phEPJC(2020)·20 citations
9. 09*

   Leading two-loop corrections to the Higgs boson self-couplings in models with extended scalar sectors

   Johannes Braathen🇯🇵 · Shinya Kanemura🇯🇵

   We compute the dominant two-loop corrections to the Higgs trilinear coupling ${\lambda }_{hhh}$ and to the Higgs quartic coupling ${\lambda }_{hhhh}$ in models with extended Higgs sectors, using the effective-potential approximation. We provide in this paper all necessary details about our calculations, and present general $\overline{\text{MS}}$ expressions for derivatives of the integrals appearing in the effective potential at two loops. We also consider three particular Beyond-the-Standard-Model (BSM) scenarios -- namely a typical scenario of an Inert Doublet Model (IDM), and scenarios of a Two-Higgs-Doublet Model (2HDM) and of a Higgs Singlet Model (HSM) without scalar mixing -- and we include all the necessary finite counterterms to obtain (in addition to $\overline{\text{MS}}$ results) on-shell scheme expressions for the corrections to the Higgs self-couplings. With these analytic results, we investigate the possible magnitude of two-loop BSM contributions to the Higgs self-couplings and the fate of the non-decoupling effects that are known to appear at one loop. We find that, at least as long as pertubative unitarity conditions are fulfilled, the size of two-loop corrections remains well below that of one-loop corrections. Typically, two-loop contributions to ${\lambda }_{hhh}$ amount to approximately 20% of those at one loop, implying that the non-decoupling effects observed at one loop are not significantly modified, but also meaning that higher-order corrections need to be taken into account for the future perspective of precise measurements of the Higgs trilinear coupling.

   hep-phEPJC(2020)·81 citations
10. 10*

    Higgs decay into massive b-quarks at NNLO QCD in the nested soft-collinear subtraction scheme

    Arnd Behring🇩🇪 · Wojciech Bizon🇩🇪

    We present a fully differential description of a decay of a scalar Higgs boson into massive b-quarks valid at next-to-next-to-leading order (NNLO) in perturbative quantum chromodynamics (QCD). We work within the nested soft-collinear subtraction scheme extended to accommodate massive partons. We include the loop-induced contribution involving a Higgs coupling to a top quark. We test our calculation against results existing in the literature, comparing the predictions for the total decay width and jet rates.

    hep-phJHEP(2020)·35 citations
11. 11*

    Theorem on vanishing contributions to ${\sin }^2{\theta }_W$ and intermediate mass scale in Grand Unified Theories with trinification symmetry

    Chandini Dash🇮🇳 · Snigdha Mishra (Berhampur University)🇮🇳 · Sudhanwa Patra (IIT Bhilai)🇮🇳

    We prove that the values of the electroweak mixing angle ${\sin }^2{\theta }_W$ and intermediate mass scale $M_I$ have vanishing contributions due to one-loop, two-loop and gravitational corrections in Grand Unified Theories which accommodate an intermediate trinification symmetry ($G_{333D}$) invoked with spontaneous D-parity mechanism operative at mass scale greater than $M_I$. The proof of theorem is robust and we verify the results numerically using supersymmetric as well as non-supersymmetric version of $E_6$-GUT.

    hep-phhep-thPRD(2020)·4 citations
12. 12*

    The full lepton flavor of little Higgs

    Jose I. Illana🇪🇸 · Jose M. Perez-Poyatos🇪🇸

    The little Higgs model with T-parity, compatible with electroweak precision constraints, introduces new flavor-mixing sources, some of which had been ignored until recently. They are reviewed here, showing that their influence does not only enrich the phenomenology of flavor-changing processes but is also needed to render finite one-loop amplitudes.

    hep-phActa Phys.Polon.B(2019)·1 citation
13. 13*

    Angular distribution of the rare decay ${\Lambda }_b\to \Lambda (\to N\pi ){\ell }^{+}{\ell }^{-}$

    Han Yan🇨🇳

    We provide a determination of the complete angular distribution for the four body rare decay ${\Lambda }_b\to \Lambda (\to N\pi ){\ell }^{+}{\ell }^{-}$, with unpolarized ${\Lambda }_b$ baryons and massive leptons, in the operator basis approach which includes the scalar, pseudo-scalar, vector, axial-vector and tensor operators. Especially, the contributions of tensor operators have been calculated for the first time in this work. Since the lepton mass is retained in our calculations, the lepton flavour universality and the decay mode ${\Lambda }_b\to \Lambda (\to N\pi ){\tau }^{+}{\tau }^{-}$ can be investigated in detail. For comparison with the experiment, we study the numerical results of observables within the Standard Model and the $S_1+S_3$ Leptoquark model. Significant deviation can be found between experiment data and the Standard Model predictions. The $S_1+S_3$ Leptoquark model can be further explored with the experimental progresses. In addition, we demonstrate the sensitivity of various angular observables to tensor operators contributions firstly, and find out that the potential New Physics effects of tensor operators can not be ignored in $b\to s{\ell }^{+}{\ell }^{-}$ transitions.

    hep-ph14 citations
14. 14*

    Strong dynamics and dark matter: investigating a minimal setup

    Benjamin Fuks🇫🇷 · Federica Giacchino🇫🇷 · Laura Lopez-Honorez🇧🇪 · Michel H.G. Tytgat🇧🇪 · Jérôme Vandecasteele🇧🇪

    We discuss the phenomenology of a dark matter scenario in which we extend the Standard Model by a real scalar particle and a vector-like heavy quark. Such a model can be seen as a simplified version of a composite setup in which the scalar field, that couples to the top quark via a Yukawa interaction with the new heavy quark, is a viable dark matter candidate. We emphasize that QCD corrections are important not only for predictions at colliders but also for direct and indirect dark matter searches and the relic abundance. We moreover show that a large fraction of the model parameter space remains unconstrained.

    hep-ph0 citations
15. 15*

    Sub-threshold $J/\psi$ and ${\rm Y}$ Production in $\gamma A$ Collisions

    Yoshitaka Hatta (BNL)🇺🇸 · Mark Strikman (PSU)🇺🇸 · Ji Xu (SJTU)🇨🇳 · Feng Yuan (LBNL)🇺🇸

    We study sub-threshold heavy quarkonium ($J/\psi$ and ${\rm Y}$) photo-productions in $\gamma A$ collisions as an independent test of the universality of the nucleon-nucleon short range correlation (SRC) in nuclear scattering processes. Just below the $\gamma p$ threshold, the cross section is dominated by the mean field contribution of nucleons inside the nucleus. The SRC contributions start to dominate at lower photon energies, depending on the fraction of the SRC pairs in the target nucleus. We give an estimate of the cross sections in the sub-threshold region both for $J/\psi$ and ${\rm Y}$. This may be helpful for future measurements at JLab as well as at the Electron-Ion Collider in the U.S., and especially in China.

    hep-phhep-exnucl-exnucl-thPLB(2020)·31 citations
16. 16*

    Dispersive construction of two-loop $P\to \pi \pi \pi$ $(P=K,\eta )$ amplitudes

    Karol Kampf🇨🇿 · Marc Knecht🇫🇷 · Jiri Novotny🇨🇿 · Martin Zdrahal🇨🇿

    We present and develop a general dispersive framework allowing us to construct representations of the amplitudes for the processes $P\pi \to \pi \pi$, $P=K,\eta$, valid at the two-loop level in the low-energy expansion. The construction proceeds through a two-step iteration, starting from the tree-level amplitudes and their S and P partial-wave projections. The one-loop amplitudes are obtained for all possible configurations of pion masses. The second iteration is presented in detail in the cases where either all masses of charged and neutral pions are equal, or for the decay into three neutral pions. Issues related to analyticity properties of the amplitudes and of their lowest partial-wave projections are given particular attention. This study is introduced by a brief survey of the situation, for both experimental and theoretical aspects, of the decay modes into three pions of charged and neutral kaons and of the eta meson.

    hep-phPRD(2020)·13 citations
17. 17*

    The Left-Right Symmetric Composite Higgs

    Cong-Sen Guan🇨🇳 · Teng Ma🇮🇱 · Jing Shu🇨🇳

    We find the exchange symmetry between left and right handed top quark in composite Higgs model with partial compositeness is efficient to soften the Higgs potential and reduce fine tuning. This symmetry can keep the Higgs potential in top sector invariant under trigonometric parity $\sin (h/f)\leftrightarrow \cos (h/f)$ and thus the Higgs quadratic divergences can be completely cancelled, resulting a UV insensitive Higgs potential. We explicitly construct the minimal left-right symmetric model based on coset space $SO(6)/SO(5)$ which is locally isomorphic to $SU(4)/Sp(4)$ and thus has well defined fermionic UV completion. This UV completion can automatically keep Higgs potential in gauge sector finite even the gauge sector breaks this discrete symmetry. We find that the vector mesons can be very heavy while the colored top partners are relatively light ($>1.5$ TeV) to obtain a light Higgs.

    hep-phhep-thPRD(2020)·8 citations
18. 18*

    Spin Density Matrix For Spin-3/2 Particles

    Jiao Jiao Song🇨🇳 · Wan Ling Chang🇨🇳

    The description of particles with spin can be attained by using a spin density matrix in high energy reaction. In this paper we present a parametrization of the spin density matrix for spin -3/2 particles in the Cartesian form. Comparing the standard form which is given by the spherical tensor operator with the Cartesian form yields four equations for the spin polarizations. These four equations can be used to eliminate the dependent spin polarizations. We also present the probabilistic interpretations of these spin polarizations by defining the spin operator in the spherical coordinate frame. These results can be used in the cross section to calculate the hadron polarizations. To illustrate this, we calculate the inclusive electron-positron annihilation process in terms of spin polarizations.

    hep-ph1 citation
19. 19*

    Gauge-flavon unification

    Alfredo Aranda🇲🇽 · Francisco J. de Anda🇲🇽 · Stephen F. King🇬🇧

    In this paper we propose the idea that flavons can emerge from extra dimensional gauge fields, referred to as gauge-flavon unification (GFU) analogous to gauge-Higgs unification (GHU). We assume that there is a gauged family symmetry in extra dimensions and that the flavons are the extra dimensional components of the gauge field. This provides a simple mechanism to align the VEVs of the flavons through a combination of Wilson lines and orbifold symmetry breaking. We present some simple 5d examples of GFU based on $SO(3)$ and $SU(4)$ gauged family symmetry, the latter case yielding $SU(3)\times U(1)$ gauged family symmetry in 4d, broken by triplet and antitriplet flavons, with effective couplings to fermions. We also present a general formalism for Wilson lines and orbifolds, in any number of dimensions, including non-commutative aspects Wilson lines, which may be useful for aligning additional flavons as required for realistic models.

    hep-phJHEP(2020)·3 citations
20. 20*

    Global Bounds on the Type-III Seesaw

    Carla Biggio🇮🇹 · Enrique Fernandez-Martinez🇪🇸 · Manuele Filaci🇮🇹 · Josu Hernandez-Garcia🇭🇺 · Jacobo Lopez-Pavon🇪🇸

    We derive general bounds on the Type-III Seesaw parameters from a global fit to flavor and electroweak precision data. We explore and compare three Type-III Seesaw realizations: a general scenario, where an arbitrary number of heavy triplets is integrated out without any further assumption, and the more constrained cases in which only 3 or 2 (minimal scenario) additional heavy states are included. The latter assumption implies rather non-trivial correlations in the Yukawa flavor structure of the model so as to reproduce the neutrino masses and mixings as measured in neutrino oscillations experiments and thus qualitative differences can be found with the more general scenario. In particular, we find that, while the bounds on most elements of the dimension 6 operator coefficients are of order $10^{-4}$ for the general and 3-triplet cases, the 2-triplet scenario is more strongly constrained with bounds between $10^{-5}$ and $10^{-7}$ for the different flavours. We also discuss how these correlations affect the present CMS constraints on the Type-III Seesaw in the minimal 2-triplet scenario.

    hep-phJHEP(2020)·27 citations
21. 21*

    Aspects of astrophysical particle production and beyond the Standard Model phenomenology

    Matthias Vereecken🇧🇪

    This PhD thesis deals with various aspects of (astro)particle physics phenomenology and consists out of two parts: beyond the Standard Model physics and neutrino astronomy. In the first part, I focus on beyond the Standard Model physics at the Large Hadron collider. Concretely, I discuss the interpretation of a 2015 excess seen by ATLAS in events with jets, missing transverse momentum and 2 same-flavour, opposite-charge leptons within a model of gauge-mediated supersymmetry breaking. Our model, which features supersymmetry breaking in multiple hidden sectors, was able to explain the 2015 data because of the appearance of an additional massive neutral particle at the bottom of the spectrum, with couplings dictated by supersymmetry. However, using more recent data, I show that this specific implementation of the model is now ruled out. In the second part, I focus on astroparticle physics and neutrino astronomy. This part consists of two projects. The first and largest of these investigates the possibility that the neutrinos seen by IceCube are produced by sources obscured by matter. We show that, in this case, existing bounds from the extragalactic gamma-ray background can be evaded. In addition, we apply our model to a set of sources selected for possible obscuration and obtain relevant bounds on the parameter space. In the final project, I investigate current constraints on neutrino emission from binary black hole mergers. While no such neutrinos are typically expected, current constraints are not yet able to rule out a substantial contribution of such events to the astrophysical neutrino flux. I show that in the near future, this possibility will be constrained. Both parts are preceded by an extensive introduction and review of their respective fields, written to be of general interest.

    hep-phastro-ph.HE1 citation
22. 22*

    Asymptotic safety with Majorana fermions and new large N equivalences

    Andrew D. Bond🇬🇧 · Daniel F. Litim🇬🇧 · Tom Steudtner🇬🇧

    Using Majorana fermions and elementary mesons we find new massless quantum field theories with weakly interacting ultraviolet fixed points. We also find new classes of large N equivalences amongst SU, SO and Sp gauge theories with different types of matter fields and Yukawa interactions. Results include a triality of asymptotically safe theories and dualities between asymptotically free matter-gauge theories with identical fixed points, phase diagrams, and scaling exponents. Implications for conformal field theory and orbifold reductions are indicated.

    ↳ hep-thhep-phPRD(2020)·33 citations
23. 23*

    Neutrino-Deuteron Reactions at Solar Neutrino Energies in Pionless Effective Field Theory with Dibaryon Fields

    Shung-Ichi Ando🇰🇷 · Young-Ho Song🇰🇷 · Chang Ho Hyun🇰🇷

    We study breakup of the deuteron induced by neutrinos in the neutral $\nu d\to \nu np$, $\bar{\nu }d\to \bar{\nu }np$ and the charged $\bar{\nu }d\to e^{+}nn$, $\nu d\to e^{-}pp$ processes. Pionless effective field theory with dibaryon fields is used to calculate the total cross sections for neutrino energies $E_{\nu }$ from threshold to 20 MeV. Amplitudes are expanded up to next-to-leading order, and the partial wave is truncated at $P$-waves. The Coulomb interaction between two protons is included nonperturbatively in the reaction amplitudes, and an analytic expression of the amplitudes is obtained. The contribution of the next-to-leading order to the total cross section is in the range of 5.2$-$9.9\% in magnitude, and that of the $P$-wave is 2.4$-$2.8\% at $E_{\nu }=20$ MeV. Uncertainty arising from an axial isovector low-energy constant is estimated to be on the order of 1\%.

    ↳ nucl-thhep-phPRC(2020)·11 citations
24. 24*

    Phase structure of the 1+1 dimensional Nambu--Jona-Lasinio model with isospin

    Michael Thies🇩🇪

    The phase diagram of the two-dimensional Nambu--Jona-Lasinio model with isospin is explored in the large Nc limit with semiclassical methods. We consider finite temperature and include chemical potentials for all conserved charges. In the chiral limit, a full analytical solution is presented, expressed in terms of known results for the single-flavor Gross-Neveu and Nambu--Jona-Lasinio models. A novel crystalline structure appears and is shown explicitly to be thermodynamically more stable than the homogeneous phase at zero temperature. If we include a bare fermion mass, the problem reduces again to solved problems in one-flavor models provided that either the fermionic or the isospin chemical potentials vanish. In the general case, a stability analysis is used to construct the perturbative phase boundary between homogeneous and inhomogeneous phases. This is sufficient to get a good overview of the complete phase diagram. Missing non-perturbative phase boundaries requiring a full numerical Hartree-Fock calculation will be presented in future work.

    ↳ hep-thhep-lathep-phPRD(2020)·28 citations
25. 25*

    Partial deconfinement in gauge theories

    Masanori Hanada🇬🇧 · Goro Ishiki🇯🇵 · Hiromasa Watanabe🇯🇵

    We provide the evidence for the existence of partially deconfined phase in large-$N$ gauge theory. In this phase, the SU($M$) subgroup of SU($N$) gauge group deconfines, where $\frac{M}{N}$ changes continuously from zero (confined phase) to one (deconfined phase). The partially deconfined phase may exist in real QCD with $N=3$.

    ↳ hep-lathep-phhep-thPoS(2019)·13 citations
26. 26*

    Entropy Production in Affine Inflation

    Hemza Azri🇦🇪 · Salah Nasri🇦🇪

    Multiple scalar fields nonminimally interacting through pure affine gravity are considered to generate primordial perturbations during an inflationary phase. The couplings considered give rise to two distinct sources of entropy perturbations that may not be suppressed in the long wavelength limit. The first is merely induced by the presence of more than one scalar and arises even in the minimal coupling limit. The second source however is restricted to nonminimal interaction. Unlike the case of metric gravity, and due to the absence of anisotropic stresses, the second source disappears for single scalar, showing that nonminimal couplings become relevant to non-adiabatic perturbations only when more than one scalar field are considered. Hence the notion of adiabaticity is not affected by the transition to minimal coupling contrary to the metric gravity case where it is confused by changing the frames. Precise data that might be able to neatly track different sources of isocurvature modes, if any, must not only distinguish between different models of inflation but also determine the most viable approach to gravity which underlies the inflationary dynamics itself.

    ↳ gr-qcastro-ph.HEhep-phhep-thPRD(2020)·11 citations
27. 27*

    Reheating in $R^2$ Palatini inflationary models

    Ioannis D. Gialamas🇬🇷 · A. B. Lahanas🇬🇷

    We consider $R^2$ inflation in the Palatini gravity assuming the existence of scalar fields, coupled to gravity in the most general manner. These theories, in the Einstein frame, and for one scalar field $h$, share common features with $K$ - inflation models. We apply this formalism for the study of popular inflationary models, whose potentials are monomials, $V\sim h^n$, with $n$ a positive even integer. We also study the Higgs model non-minimally coupled to gravity. Although these have been recently studied, in the framework of the Palatini approach, we show that the scalar power spectrum severely constrains these models. Although we do not propose a particular reheating mechanism, we show that the quadratic $\sim h^2$ and the Higgs model can survive these constraints with a maximum reheating temperature as large as $\sim 10^{15}GeV$, when reheating is instantaneous. However, this can be only attained at the cost of a delicate fine-tuning of couplings. Deviations from this fine-tuned values can still yield predictions compatible with the cosmological data, for couplings that lie in very tight range, giving lower reheating temperatures.

    ↳ gr-qcastro-ph.COhep-phhep-thPRD(2020)·118 citations
28. 28*

    Continuous $\beta$ function for the SU(3) gauge systems with two and twelve fundamental flavors

    Anna Hasenfratz🇺🇸 · Oliver Witzel🇺🇸

    The gradient flow transformation can be interpreted as continuous real-space renormalization group transformation if a coarse-graining step is incorporated as part of calculating expectation values. The method allows to predict critical properties of strongly coupled systems including the renormalization group $\beta$ function and anomalous dimensions at nonperturbative fixed points. In this contribution we discuss a new analysis of the continuous renormalization group $\beta$ function for $N_f=2$ and $N_f=12$ fundamental flavors in SU(3) gauge theories based on this method. We follow the approach developed and tested for the $N_f=2$ system in arXiv:1910.06408. Here we present further information on the analysis, emphasizing the robustness and intuitive features of the continuous $\beta$ function calculation. We also discuss the applicability of the continuous $\beta$ function calculation in conformal systems, extending the possible phase diagram to include a 4-fermion interaction. The numerical analysis for $N_f=12$ uses the same set of ensembles that was generated and analyzed for the step scaling function in arXiv:1909.05842. The new analysis uses volumes with $L\ge 20$ and determines the $\beta$ function in the $c=0$ gradient flow renormalization scheme. The continuous $\beta$ function predicts the existence of a conformal fixed point and is consistent between different operators. Although determinations of the step scaling and continuous $\beta$ function use different renormalization schemes, they both predict the existence of a conformal fixed point around $g^2\sim 6$.

    ↳ hep-lathep-phhep-thPoS(2019)·19 citations
29. 29*

    Study of thermal SU(3) supersymmetric Yang-Mills theory and near-conformal theories from the gradient flow

    Georg Bergner🇩🇪 · Camilo López🇩🇪 · Stefano Piemonte🇩🇪

    We compute the renormalization group flow of the mass anomalous dimension in adjoint QCD with $N_f=1$, $3/2$, and 2 Dirac fermions, using the gradient flow. Preliminary results are in agreement with at least a near-conformal scenario in all cases. At the largest flavor numbers we obtain the strongest indication for an IR conformal fixed point scenario. Moreover, we provide results for the thermal phase transitions in SU(3) supersymmetric Yang-Mills theory. We find hints for a connection between chiral and center symmetries in terms of a single first order phase transition where chiral symmetry is restored and center symmetry gets broken.

    ↳ hep-lathep-phhep-thPoS(2019)·7 citations
30. 30*

    Parton Distribution Functions of Heavy Mesons on the Light Front

    Jiangshan Lan🇨🇳 · Chandan Mondal🇨🇳 · Meijian Li🇺🇸 · Yang Li🇺🇸 · Shuo Tang🇺🇸 · Xingbo Zhao🇨🇳 · James P. Vary🇺🇸

    The parton distribution functions (PDFs) of heavy mesons are evaluated from their light-front wave functions, which are obtained from a basis light-front quantization in the leading Fock sector representation. We consider the mass eigenstates from an effective Hamiltonian consisting of the confining potential adopted from light-front holography in the transverse direction, a longitudinal confinement, and a one-gluon exchange interaction with running coupling. We present the gluon and the sea quark PDFs which we generate dynamically from the QCD evolution of the valence quark distributions.

    ↳ nucl-thhep-phPRD(2020)·68 citations
31. 31*

    AION: An Atom Interferometer Observatory and Network

    L. Badurina🇬🇧 · E. Bentine🇬🇧 · D. Blas🇬🇧 · K. Bongs🇬🇧 · D. Bortoletto🇬🇧 · T. Bowcock🇬🇧 · K. Bridges🇬🇧 · W. Bowden🇬🇧 · O. Buchmueller🇬🇧 · C. Burrage🇬🇧 · J. Coleman🇺🇸 · G. Elertas🇬🇧 and 29 other authors

    We outline the experimental concept and key scientific capabilities of AION (Atom Interferometer Observatory and Network), a proposed UK-based experimental programme using cold strontium atoms to search for ultra-light dark matter, to explore gravitational waves in the mid-frequency range between the peak sensitivities of the LISA and LIGO/Virgo/ KAGRA/INDIGO/Einstein Telescope/Cosmic Explorer experiments, and to probe other frontiers in fundamental physics. AION would complement other planned searches for dark matter, as well as probe mergers involving intermediate mass black holes and explore early universe cosmology. AION would share many technical features with the MAGIS experimental programme in the US, and synergies would flow from operating AION in a network with this experiment, as well as with other atom interferometer experiments such as MIGA, ZAIGA and ELGAR. Operating AION in a network with other gravitational wave detectors such as LIGO, Virgo and LISA would also offer many synergies.

    ↳ astro-ph.COgr-qchep-exhep-ph+1JCAP(2020)·456 citations
32. 32*

    Early dark energy from massive neutrinos -- a natural resolution of the Hubble tension

    Jeremy Sakstein🇺🇸 · Mark Trodden🇺🇸

    The Hubble tension can be significantly eased if there is an early component of dark energy that becomes active around the time of matter-radiation equality. Early dark energy models suffer from a coincidence problem -- the physics of matter-radiation equality and early dark energy are completely disconnected, so some degree of fine-tuning is needed in order for them to occur nearly simultaneously. In this paper we propose a natural explanation for this coincidence. If the early dark energy scalar couples to neutrinos then it receives a large injection of energy around the time that neutrinos become non-relativistic. This is precisely when their temperature is of order their mass, which, coincidentally, occurs around the time of matter-radiation equality. Neutrino decoupling therefore provides a natural trigger for early dark energy by displacing the field from its minimum just before matter-radiation equality. We discuss various theoretical aspects of this proposal, potential observational signatures, and future directions for its study.

    ↳ astro-ph.COgr-qchep-phhep-thPRL(2020)·296 citations
33. 33*

    The halo mass function in alternative dark matter models

    M. R. Lovell (University of Iceland)🇮🇸

    The claimed detection of large amounts of substructure in lensing flux anomalies, and in Milky Way stellar stream gaps statistics, has lead to a step change in constraints on simple warm dark matter models. In this study we compute predictions for the halo mass function both for these simple models and also for comprehensive particle physics models of sterile neutrinos and dark acoustic oscillations. We show that the mass function fit of Lovell et al. underestimates the number of haloes less massive than the half-mode mass, $M_{\mathrm{hm}}$ by a factor of 2, relative to the extended Press-Schechter (EPS) method. The alternative approach of applying EPS to the Viel et al. matter power spectrum fit instead suggests good agreement at $M_{\mathrm{hm}}$ relative to the comprehensive model matter power spectra results, although the number of haloes with mass $<M_{\mathrm{hm}}$ is still suppressed due to the absence of small scale power in the fitting function. Overall, we find that the number of dark matter haloes with masses $<10^8{M}_{\odot }$ predicted by competitive particle physics models is underestimated by a factor of $\sim 2$ when applying popular fitting functions, although careful studies that follow the stripping and destruction of subhaloes will be required in order to draw robust conclusions.

    ↳ astro-ph.COhep-phMNRAS(2020)·24 citations
34. 34*

    Optimal event selection and categorization in high energy physics, Part 1: Signal discovery

    Konstantin K. Matchev🇺🇸 · Prasanth Shyamsundar🇺🇸

    We provide a prescription to train optimal machine-learning-based event selectors and categorizers that maximize the statistical significance of a potential signal excess in high energy physics (HEP) experiments, as quantified by any of six different performance measures. For analyses where the signal search is performed in the distribution of some event variables, our prescription ensures that only the information complementary to those event variables is used in event selection and categorization. This eliminates a major misalignment with the physics goals of the analysis (maximizing the significance of an excess) that exists in the training of typical ML-based event selectors and categorizers. In addition, this decorrelation of event selectors from the relevant event variables prevents the background distribution from becoming peaked in the signal region as a result of event selection, thereby ameliorating the challenges imposed on signal searches by systematic uncertainties. Our event selectors (categorizers) use the output of machine-learning-based classifiers as input and apply optimal selection cutoffs (categorization thresholds) that depend on the event variables being analyzed, as opposed to flat cutoffs (thresholds). These optimal cutoffs and thresholds are learned iteratively, using a novel approach with connections to Lloyd's k-means clustering algorithm. We provide a public, Python 3 implementation of our prescription called ThickBrick, along with usage examples.

    ↳ physics.data-anhep-exhep-phphysics.comp-phJHEP(2021)·4 citations
35. 35*

    Topological Eternal Hilltop Inflation and the Swampland Criteria

    Chia-Min Lin🇹🇼

    The swampland criteria put significant constraints on inflation models. In this paper, I show that hilltop inflation on the brane may provide an initial condition for hilltop inflation and produce topological eternal inflation without violating the swampland distance and refined de Sitter criteria. This shows a way that string theory may not be incompatible with eternal inflation.

    ↳ hep-thgr-qchep-phJCAP(2020)·23 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.