Mon·Mar 9, 2020Monday·March 9, 2020

1. 01*

   Improved opacity expansion for medium-induced parton splitting

   Yacine Mehtar-Tani🇺🇸

   We revisit the calculation of the medium-induced gluon radiative spectrum and propose a novel expansion scheme that encompasses the two known analytic limits: i) the high frequency regime dominated by a single hard scattering that corresponds to the leading order in the standard opacity expansion, ii) the low frequency regime that is dominated by multiple soft scatterings. Our approach is based on expanding around the harmonic oscillator instead of vacuum in the leading logarithmic approximation. We compute the first two orders in this improved opacity expansion and show that they account for the aforementioned limits.

   hep-phnucl-thNPA(2021)·0 citations
2. 02*

   On the breaking of Casimir scaling in jet quenching

   Liliana Apolinário🇵🇹 · João Barata🇪🇸 · Guilherme Milhano🇵🇹

   We study the breaking of Casimir scaling, $C_F/C_A$, due to the evolution of jets in a hot and extended medium. By using JEWEL, a medium modified Monte Carlo event generator validated for a wide set of observables, we are able to study separately the development of quark and gluon-initiated jets produced back-to-back with a $Z-$boson. Focusing on the $p_T$ distribution, we conclude first that the colour charge ratio is constant but larger than Casimir scaling for high $p_T$ jets. In addition, our results seem to indicate that the medium induced cascade is more similar between quarks and gluons, thus driving the overall medium shower scaling away from the vacuum expectation. Finally, we compare our results to another Monte Carlo generator and observe the same scaling violation.

   hep-phEPJC(2020)·15 citations
3. 03*

   Lepton Pair Production Through Two Photon Process in Heavy Ion Collisions

   Spencer Klein🇺🇸 · Al Mueller🇺🇸 · Bo-Wen Xiao🇨🇳 · Feng Yuan🇺🇸

   This paper investigates the electromagnetic production of lepton pairs with low transverse momentum in relativistic heavy ion collisions. We estimate the initial photons' transverse momentum contributions by employing models where the average transverse momentum squared of the incoming photon can be calculated in the equivalent photon approximation. We further derive an all order QED resummation for the soft photon radiation, which gives an excellent description of the ATLAS data in ultra-peripheral collisions at the LHC. For peripheral and central collisions, additional $p_T$-broadening effects from multiple interaction with the medium and the magnetic field contributions from the quark-gluon plasma are also discussed.

   hep-phhep-exnucl-exnucl-thPRD(2020)·90 citations
4. 04*

   Scotogenic dark matter and Dirac neutrinos from unbroken gauged $B-L$ symmetry

   Julio Leite🇧🇷 · América Morales🇲🇽 · José W. F. Valle🇪🇸 · Carlos A. Vaquera-Araujo🇲🇽

   We propose a simple extension of the standard model where neutrinos get naturally small "scotogenic" Dirac masses from an unbroken gauged $B-L$ symmetry, ensuring dark matter stability. The associated gauge boson gets mass through the Stueckelberg mechanism. Two scenarios are identified, and the resulting phenomenology briefly sketched.

   hep-phPLB(2020)·32 citations
5. 05*

   The contributions of the vector-channel at finite isospin chemical potential with the self-consistent mean field approximation

   Zu-Qing Wu🇨🇳 · Chao-Shi🇨🇳 · Jia-Lun Ping🇨🇳 · Hong-Shi Zong🇨🇳

   The self-consistent mean field approximation of two-flavor NJL model, which introduces a free parameter $\alpha$ ($\alpha$ reflects the weight of different interaction channels), is employed to investigate the contributions of the vector-channel at finite isospin chemical potential ${\mu }_I$ and zero baryon chemical potential ${\mu }_B$ and zero temperature $T$. The calculations show that the consideration of the vector-channel contributions leads to lower value of pion condensate in superfluid phase, compared with the standard Lagrangian of NJL model ($\alpha =0$). In superfluid phase, we also obtain lower isospin number density, and the discrepancy is getting larger with the increase of isospin potential. Compared with the recent results from Lattice QCD, the isospin density and energy density we obtained with $\alpha =0.5$ agree with the data of lattice well. In the phase diagram in the $T-{\mu }_I$ plane for ${\mu }_B=0$, we can see that the difference of the critical temperatures of phase transition between the results with $\alpha =0$ and $\alpha =0.5$ is up to $3\%-5\%$ for a fixed isospin potential. All of these indicate that the vector channels play an important role in isospin medium.

   hep-phnucl-thPRD(2020)·9 citations
6. 06*

   QED and QCD helicity amplitudes in parton-shower gauge

   Kaoru Hagiwara🇯🇵 · Junichi Kanzaki🇯🇵 · Kentarou Mawatari🇯🇵

   We introduce photon and gluon propagators in which the scalar polarization component is subtracted systematically by making use of the BRST invariance of the off-shell vector boson created from physical on-shell states. The propagator has the light-cone gauge form, where the spacial component of the gauge vector points along the negative of the off-shell vector boson momentum. We call the gauge as parton-shower gauge, since in collinear configurations the absolute value squared of each Feynman amplitude reproduces all the singular behaviors of the corresponding parton shower in this gauge. We introduce new HELAS codes that can be used to calculate the tree-level helicity amplitudes of arbitrary QED and QCD processes by using MadGraph. The absence of subtle gauge cancellation among Feynman amplitudes allows numerical codes to evaluate singular behaviors accurately, and helps us gaining physical insights on interference patterns.

   hep-phEPJC(2020)·14 citations
7. 07*

   Spatial and Momentum Imaging of the Pion and Kaon

   Chao Shi🇨🇳 · Kyle Bednar🇺🇸 · Ian C. Cloët🇺🇸 · Adam Freese🇺🇸

   We determine the leading Fock state light front wave functions (LFWFs) of the pion and kaon via light front projections of the covariant Bethe-Salpeter wave function. Using these LFWFs we study the multi-dimensional images of the valence quarks in the pion and kaon that are provided by their generalized parton distribution functions (GPDs) and transverse momentum dependent parton distribution functions (TMDs). Moments of the GPDs are taken to obtain the electromagnetic and gravitational form factors of the pion and kaon, and comparisons to available experimental and lattice data are made. Highlights from this study include predictions that the mean-squared impact parameter for the quarks in the pion and kaon are: $⟨{\vec{b}}_T^2{⟩}_u^{\pi }=0.11$fm${}^2$, $⟨{\vec{b}}_T^2{⟩}_s^K=0.08$fm${}^2$, and $⟨{\vec{b}}_T^2{⟩}_u^K=0.13$fm${}^2$, and therefore the $s$ quark in the kaon is much closer to the center of transverse momentum than the $u$ quark. From the electromagnetic and gravitational form factors we find that the light-cone energy radii are about 60\% smaller than the light-cone charge radii for each quark sector in the pion and kaon. A quantitative measure of the importance of the leading Fock state is obtained via comparison with a full DSE calculation (containing an infinite tower of Fock states) for the pion form factor.

   hep-phnucl-thPRD(2020)·40 citations
8. 08*

   Higgs-Pair Production via Gluon Fusion at Hadron Colliders: NLO QCD Corrections

   J. Baglio🇨🇭 · F. Campanario🇪🇸 · S. Glaus🇩🇪 · M. M. Muhlleitner🇩🇪 · J. Ronca🇪🇸 · M. Spira🇨🇭 · J. Streicher🇩🇪

   Higgs-pair production via gluon fusion is the dominant production mechanism of Higgs-boson pairs at hadron colliders. In this work, we present details of our numerical determination of the full next-to-leading-order (NLO) QCD corrections to the leading top-quark loops. Since gluon fusion is a loop-induced process at leading order, the NLO calculation requires the calculation of massive two-loop diagrams with up to four different mass/energy scales involved. With the current methods, this can only be done numerically, if no approximations are used. We discuss the setup and details of our numerical integration. This will be followed by a phenomenological analysis of the NLO corrections and their impact on the total cross section and the invariant Higgs-pair mass distribution. The last part of our work will be devoted to the determination of the residual theoretical uncertainties with special emphasis on the uncertainties originating from the scheme and scale dependence of the (virtual) top mass. The impact of the trilinear Higgs-coupling variation on the total cross section will be discussed.

   hep-phhep-exJHEP(2020)·103 citations
9. 09*

   Lepton Flavor Universality Violation in a 331 Model in $b\to s{l}^{+}{l}^{-}$ Processes

   Soumia Lebbal🇩🇿 · Noureddine Mebarki🇩🇿 · Jamal Mimouni🇩🇿

   Lepton Flavor Universality Violation (LFUV) in $b\to s{l}^{+}{l}^{-}$ processes is investigated in the context of a 331 model. It is shown that in order to explain the experimentally observed deviations from the Standard Model in these FCNC transitions, a non-minimal version of the model has to be considered. We investigate the ability of this model in accomodating the model-independant scenarios currently favored by global fits.

   hep-ph3 citations
10. 10*

    Electroproduction of a large invariant mass photon pair

    A.Pedrak🇵🇱 · B.Pire🇫🇷 · L.Szymanowski🇵🇱 · J.Wagner🇵🇱

    We study the exclusive electroproduction of a photon pair in the kinematical regime where the diphoton invariant mass is large and where the nucleon flies almost in its original direction. We discuss the relative importance of the QCD process where the two photons originate from a quark line compared to the single (double) Bethe-Heitler processes where one (two) photons originate from the lepton line. This process turns out to be a promising tool to study generalized parton distributions in the nucleon, both at the medium energy of JLab and at a high energy electron ion collider.

    hep-phPRD(2020)·47 citations
11. 11*

    Thermalization and dynamical spectral properties in the quark-meson model

    Linda Shen🇩🇪 · Jürgen Berges🇩🇪 · Jan M. Pawlowski🇩🇪 · Alexander Rothkopf🇳🇴

    We investigate the nonequilibrium evolution of the quark-meson model using two-particle irreducible effective action techniques. Our numerical simulations, which include the full dynamics of the order parameter of chiral symmetry, show how the model thermalizes into different regions of its phase diagram. In particular, by studying quark and meson spectral functions, we shed light on the real-time dynamics approaching the crossover transition, revealing e.g. the emergence of light effective fermionic degrees of freedom in the infrared. At late times in the evolution, the fluctuation-dissipation relation emerges naturally among both meson and quark degrees of freedom, confirming that the simulation successfully reaches thermal equilibrium.

    hep-phPRD(2020)·17 citations
12. 12*

    Multiplicity distribution of gluons in pQCD

    G.H. Arakelyan🇦🇲 · Yu.M. Shabelski🇷🇺 · A.G. Shuvaev🇷🇺

    The multiplicity distribution of the gluons produced at the high energy is evaluated in BFKL approach. The distribution has Poisson form that can explain experimentally observed KNO scaling.

    hep-phEPJC(2020)·2 citations
13. 13*

    Tsallis-thermometer: a QGP indicator for large and small collisional systems

    Gábor Bíró🇭🇺 · Gergely Gábor Barnaföldi🇭🇺 · Tamás Sándor Biró🇭🇺

    The transverse momentum distribution of identified hadrons from recent years are analyzed within the thermodynamically consistent formulation of non-extensive statistics. A wide range of center-of-mass energies and average event multiplicities are studied for various hadron species. We demonstrate that the average event multiplicity is a key variable in the study of high-energy collisions and a smooth transition in the description from small to large systems is possible. For this purpose the non-extensive statistical approach is more than appropriate. The validity of the non-extensive description is explored in multiple ways: such as the calculation of integrated yields per unit rapidity, the analysis of radial flow and the consistency check of the thermodynamical variables. The 'Tsallis-thermometer' is introduced as an indicator of quark-gluon plasma in small collisional systems.

    hep-phnucl-thJ.Phys.G(2020)·50 citations
14. 14*

    Proton Decay: Flipped vs Unflipped SU(5)

    John Ellis🇬🇧 · Marcos A. G. Garcia🇪🇸 · Natsumi Nagata🇯🇵 · Dimitri V. Nanopoulos🇺🇸 · Keith A. Olive🇺🇸

    We analyze nucleon decay modes in a no-scale supersymmetric flipped SU(5) GUT model, and contrast them with the predictions for proton decays via dimension-6 operators in a standard unflipped supersymmetric SU(5) GUT model. We find that these GUT models make very different predictions for the ratios $\Gamma (p\to {\pi }^0{\mu }^{+})/\Gamma (p\to {\pi }^0{e}^{+})$, $\Gamma (p\to {\pi }^{+}\bar{\nu })/\Gamma (p\to {\pi }^0{e}^{+})$, $\Gamma (p\to K^0{e}^{+})/\Gamma (p\to {\pi }^0{e}^{+})$ and $\Gamma (p\to K^0{\mu }^{+})/\Gamma (p\to {\pi }^0{\mu }^{+})$, and that predictions for the ratios $\Gamma (p\to {\pi }^0{\mu }^{+})/\Gamma (p\to {\pi }^0{e}^{+})$ and $\Gamma (p\to {\pi }^{+}\bar{\nu })/\Gamma (p\to {\pi }^0{e}^{+})$ also differ in variants of the flipped SU(5) model with normal- or inverse-ordered light neutrino masses. Upcoming large neutrino experiments may have interesting opportunities to explore both GUT and flavour physics in proton and neutron decays.

    hep-phJHEP(2020)·35 citations
15. 15*

    Confronting same-sign W-boson production with parton correlations

    Sabrina Cotogno🇫🇷 · Tomas Kasemets🇩🇪 · Miroslav Myska🇨🇿

    The future runs of LHC offer a unique opportunity to measure correlations between two partons inside the proton, which have never been experimentally detected. The process of interest is the production of two positively charged W-bosons decaying in the muon channel. We present a detailed analysis of proton-proton collisions at $\sqrt{s}$ = 13 TeV, where we combine Monte Carlo event generators with our calculations of parton correlations. We carefully compare double parton scattering to relevant background processes and trace a path towards a clean signal sample. Several observables are constructed to demonstrate the effect of parton correlations with respect to clear benchmark values for uncorrelated scatterings. We find that especially spin correlations can be responsible for large effects in the variables we study, because of their direct relation with the parton angular momentum and, therefore, the directions of the muon momenta. We estimate the significance of the measurements as a function of the integrated luminosity and conclude that the LHC has the potential to detect, or put strong limits on, parton correlations in the near future.

    hep-phhep-exJHEP(2020)·16 citations
16. 16*

    The Ground State Calculations for Some Nuclei by Mesonic Potential of Nucleon-Nucleon Interaction

    K.M.Hanna🇪🇬 · SH.M.Sewailem🇪🇬 · R.Hussien🇪🇬 · L. I. Abou-Salem🇪🇬 · Asmaa.G.Shalaby🇪🇬

    The interaction of Nucleon-Nucleon (NN) has certain physical characteristics, which indicated by nucleon, and meson degrees of freedom. The main purpose of this work is calculating the ground state energies of 21 Deutron and Alfa through the two-body system with the exchange of mesons (Pi, segma, omega) that mediated between two nucleons. This paper investigates NN interaction based on the quasi-relativistic decoupled Dirac equation and self-consistent Hartree-Fock formulation. We construct one-boson exchange potential (OBEP) model, where each nucleon is treated as a Dirac particle and acts as a source of pseudoscalar, scalar, and vector fields. The potential in the present work is analytically derived with two static functions of meson, the single particle energy dependent(SPED) and generalized Yukawa (GY) functions, the parameters used in meson functions are just published ones (mass, coupling constant,and cut o? parameters). The theoretical results are compared to other theoretical models and their corresponding experimental data, one can see that the SPED function gives more satisfied agreement than the GY function in case of the considered nuclei.

    hep-phnucl-thAdv.High Energy Phys.(2020)·1 citation
17. 17*

    On sub-GeV Dark Matter Production at Fixed-Target Experiments

    Asher Berlin🇺🇸 · Patrick deNiverville🇰🇷 · Adam Ritz🇨🇦 · Philip Schuster🇺🇸 · Natalia Toro🇺🇸

    We analyze the sensitivity of fixed-target experiments to sub-GeV thermal relic dark matter models, accounting for variations in both mediator and dark matter mass, and including dark matter production through both on- and off-shell mediators. It is commonly thought that the sensitivity of such experiments is predicated on the existence of an on-shell mediator that is produced and then decays to dark matter. While accelerators do provide a unique opportunity to probe the mediator directly, our analysis demonstrates that their sensitivity extends beyond this commonly discussed regime. In particular, we provide sensitivity calculations that extend into both the effective field theory regime where the mediator is much heavier than the dark matter and the regime of an off-shell mediator lighter than a dark matter particle-antiparticle pair. Our calculations also elucidate the resonance regime, making it clear that all but a fine-tuned region of thermal freeze-out parameter space for a range of simple models is well covered.

    hep-phhep-exPRD(2020)·53 citations
18. 18*

    Neutrino Non-Standard Interactions: Complementarity Between LHC and Oscillation Experiments

    K.S. Babu🇺🇸 · Dorival Gonçalves🇺🇸 · Sudip Jana🇩🇪 · Pedro A. N. Machado🇺🇸

    We explore the complementarity between LHC searches and neutrino experiments in probing neutrino non-standard interactions. Our study spans the theoretical frameworks of effective field theory, simplified model and an illustrative UV completion, highlighting the synergies and distinctive features in all cases. We show that besides constraining the allowed NSI parameter space, the LHC data can break important degeneracies present in oscillation experiments such as DUNE, while the latter play an important role in probing light and weakly coupled physics undetectable at the LHC.

    hep-phhep-exPLB(2021)·44 citations
19. 19*

    Resolving electron and muon $g-2$ within the 2HDM

    Sudip Jana🇩🇪 · Vishnu P.K. · Shaikh Saad🇺🇸

    Recent precise measurement of the electron anomalous magnetic moment (AMM) adds to the longstanding tension of the muon AMM and together strongly point towards physics beyond the Standard Model (BSM). In this work, we propose a solution to both anomalies in an economical fashion via a light scalar that emerges from a second Higgs doublet and resides in the $\mathcal{O}(10)$-MeV to $\mathcal{O}(1)$-GeV mass range yielding the right sizes and signs for these deviations due to one-loop and two-loop dominance for the muon and the electron, respectively. A scalar of this type is subject to a number of various experimental constraints, however, as we show, it can remain sufficiently light by evading all experimental bounds and has the great potential to be discovered in the near-future low-energy experiments. The analysis provided here is equally applicable to any BSM scenario for which a light scalar is allowed to have sizable flavor-diagonal couplings to the charged leptons. In addition to the light scalar, our theory predicts the existence of a nearly degenerate charged scalar and a pseudoscalar, which have masses of the order of the electroweak scale. We analyze possible ways to probe new-physics signals at colliders and find that this scenario can be tested at the LHC by looking at the novel process $pp\to H^{\pm }{H}^{\pm }jj\to l^{\pm }{l}^{\pm }jj+{E/}_T$ via same-sign pair production of charged Higgs bosons.

    hep-phhep-exhep-latPRD(2020)·101 citations
20. 20*

    $Y(4260)$ as four-quark state

    Anna Zuzana Dubnickova🇸🇰 · Stanislav Dubnicka🇸🇰 · Aidos Issadykov🇷🇺 · Mikhail Alekseevich Ivanov🇷🇺 · Andrej Liptaj🇸🇰

    We treat the $Y(4260)$ resonance as a four-quark state in the framework of the covariant confining quark model. We study two choices of the interpolating current, either the molecular-type current which effectively corresponds to the product of $D$ and ${\bar{D}}_1$ quark currents or tetraquark one. In both cases we calculate the widths of decays $Y(4260)\to Z_c(3900)+\pi$ and $Y(4260)\to D^{(\ast )}+{\bar{D}}^{(\ast )}$. It is found that in both approches the mode $Y\to Z_c^{+}+{\pi }^{-}$ is enhanced compared with the open charm modes. However the absolute value of the $Y\to Z_c^{+}+{\pi }^{-}$ decay width obtained in molecular picture is arguably too large. On the other hand the value obtained in tetraquark picture is reasonable.

    hep-phnucl-thPRD(2020)·17 citations
21. 21*

    Plasma Lenses: Possible alternative OMD at the ILC

    Manuel Formela🇩🇪 · Niclas Hamann🇩🇪 · Klaus Floettmann🇩🇪 · Gudrid Moortgat-Pick🇩🇪 · Sabine Riemann🇩🇪 · Andriy Ushakov🇩🇪

    In the baseline design of the International Linear Collider (ILC) an undulator-based source is foreseen for the positron source in order to match the physics requirements. The recently chosen first energy stage with sqrt(s)=250 GeV requires high luminosity and imposes an effort for all positron source designs at high-energy colliders. In this paper we perform a simulation study and adopt the new technology of plasma lenses to capture the positrons generated by the undulator photons and to create the required high luminosity positron beam.

    ↳ physics.acc-phhep-ph0 citations
22. 22*

    Annual modulations from secular variations: not relaxing DAMA?

    Andrea Messina🇮🇹 · Marco Nardecchia🇮🇹 · Stefano Piacentini🇮🇹

    In a recent paper [arXiv:2002.00459], Buttazzo et al. show how the annually modulated rate of the DAMA experiments can be possibly interpreted as an artefact due to the interplay between a time-dependent background and the method to account for it. In this work, we compare this hypothesis against the sinusoidal dark matter signal as proposed by the DAMA collaboration. We produce in a Bayesian approach a quantitative comparison of how much the experimental observations are in support of each hypothesis. Our conclusions are that the odds against the hypothesis of a time varying background being responsible for the annual modulation are decreased by a Bayes factor larger than 10^8 after considering the public available data of the DAMA/NaI and DAMA/LIBRA experiments. In this work we also elaborate on general aspects of the analysis procedure. Indeed, in order to optimise the background subtraction procedure, the DAMA collaboration only considers data-taking cycles with a duration of roughly one year. We argue that any data-taking cycle is informative, and we propose a procedure to include this effect, as well as the possibility to include a slowly varying component for the background.

    ↳ hep-exastro-ph.COhep-phJCAP(2020)·21 citations
23. 23*

    Characterizing the continuous gravitational-wave signal from boson clouds around Galactic isolated black holes

    Sylvia J. Zhu🇩🇪 · Masha Baryakhtar🇺🇸 · Maria Alessandra Papa🇩🇪 · Daichi Tsuna🇯🇵 · Norita Kawanaka🇯🇵 · Heinz-Bernd Eggenstein🇩🇪

    Ultralight bosons can form large clouds around stellar-mass black holes via the superradiance instability. Through processes such as annihilation, these bosons can source continuous gravitational wave signals with frequencies within the range of LIGO and Virgo. If boson annihilation occurs, then the Galactic black hole population will give rise to many gravitational signals; we refer to this as the ensemble signal. We characterize the ensemble signal as observed by the gravitational-wave detectors; this is important because the ensemble signal carries the primary signature that a continuous wave signal has a boson annihilation origin. We explore how a broad set of black hole population parameters affects the resulting spin-0 boson annihilation signal and consider its detectability by recent searches for continuous gravitational waves. A population of $10^8$ black holes with masses up to $30{\mathrm{M}}_{\odot }$ and a flat dimensionless initial spin distribution between zero and unity produces up to a thousand signals loud enough to be in principle detected by these searches. For a more moderately spinning population the number of signals drops by about an order of magnitude, still yielding up to a hundred detectable signals for some boson masses. A non-detection of annihilation signals at frequencies between 100 and 1200 Hz disfavors the existence of scalar bosons with rest energies between $2\times 10^{-13}$ and $2.5\times 10^{-12}$ eV. Finally we show that, depending on the black hole population parameters, care must be taken in assuming that the continuous wave upper limits from searches for isolated signals are still valid for signals that are part of a dense ensemble: Between 200 and 300 Hz, we urge caution when interpreting a null result for bosons between 4 and $6\times 10^{-13}$ eV.

    ↳ gr-qcastro-ph.HEhep-phPRD(2020)·132 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.