Fri·Jul 3, 2020Friday·July 3, 2020

1. 01*

   Next-to-leading order Balitsky-Kovchegov equation beyond large $N_{\mathrm{c}}$

   T. Lappi🇫🇮 · H. Mäntysaari🇫🇮 · A. Ramnath🇫🇮

   We calculate finite-$N_{\mathrm{c}}$ corrections to the next-to-leading order (NLO) Balitsky-Kovchegov (BK) equation. We find analytical expressions for the necessary correlators of six Wilson lines in terms of the two-point function using the Gaussian approximation. In a suitable basis, the problem reduces from the diagonalization of a six-by-six matrix to the diagonalization of a three-by-three matrix, which can easily be done analytically. We study numerically the effects of these finite-$N_{\mathrm{c}}$ corrections on the NLO BK equation. In general, we find that the finite-$N_{\mathrm{c}}$ corrections are smaller than the expected $1/N_{\mathrm{c}}^2\sim 10\%$. The corrections may be large for individual correlators, but have less of an influence on the shape of the amplitude as a function of the dipole size. They have an even smaller effect on the evolution speed as a function of rapidity.

   hep-phnucl-thPRD(2020)·30 citations
2. 02*

   Energy scan/dependence of kinetic freeze-out scenarios of multi-strange and other identified particles in central nucleus-nucleus collisions

   Muhammad Waqas🇨🇳 · Fu-Hu Liu🇨🇳 · Rui-Qin Wang🇨🇳 · Irfan Siddique🇨🇳

   The transverse momentum (mass) spectra of the multi-strange and non-multi-strange (i.e. other identified) particles in central gold-gold (Au-Au), lead-lead (Pb-Pb), argon-muriate (Ar-KCl) and nickel-nickel (Ni-Ni) collisions over a wide energy range have been studied in this work. The experimental data measured by various collaborations have been analyzed. The blast-wave fit with Tsallis statistics is used to extract the kinetic freeze-out temperature and transverse flow velocity from the experimental data of transverse momentum (mass) spectra. The extracted parameters increase with the increase of collision energy and appear with the trend of saturation at the Beam Energy Scan (BES) energies at the Relativistic Heavy Ion Collider (RHIC). This saturation implies that the onset energy of phase transition of partial deconfinement is 7.7 GeV and that of whole deconfinement is 39 GeV. Furthermore, the energy scan/dependence of kinetic freeze-out scenarios are observed for the multi-strange and other identified particles, though the multiple freeze-out scenarios are also observed for various particles.

   hep-phhep-exnucl-exnucl-thEPJA(2020)·41 citations
3. 03*

   The KSVZ Axion and Pseudo-Nambu-Goldstone Boson Models for the XENON1T Excess

   Tianjun Li🇨🇳

   The XENON1T excess can be explained by the Axion Like Particle (ALP) dark matter with mass around 2.5 keV. However, there are three problems needed to be solved: suppressing the coupling $g_{a\gamma }$ between the ALP and photon, and generating the proper coupling $g_{ae}$ between the ALP and electron as well as the correct ALP mass. We propose three models to solve these problems. In our models, the $g_{ae}$ couplings are produced by integrating out the vector-like leptons, and the correct ALP masses arise from high-dimensional operators. In the KSVZ axion model, the coupling $g_{a\gamma }$ can be suppressed by choosing proper sets of vector-like fermions, but we need some fine-tunings to obtain the ALP mass. Similarly, one can study the DFSZ axion model. In the $Z_8$ and $U(1{)}_X$ models with approximate Pseudo-Nambu-Goldstone Bosons (PNGBs), the coupling $g_{a\gamma }$ is suppressed due to $SU(3{)}_C\times U(1{)}_{\mathrm{EM}}$ anomaly free. In the $Z_8$ model, the PNGB mass can be generated naturally at the keV scale via the dimension-8 operator. To solve the PNGB quality problem in the $Z_8$ model, we embed it into the model with $U(1{)}_X$ gauge symmetry.

   hep-phhep-ex28 citations
4. 04*

   Color-electric conductivity in a viscous quark-gluon plasma

   Bing-feng Jiang🇨🇳 · Shao-wu Shi🇨🇳 · De-fu Hou🇨🇳 · Jia-rong Li🇨🇳

   Several different transport processes, such as heat transport, momentum transport and charge transport, may take place at the same time in the quark-gluon plasma (QGP). The corresponding transport coefficients are heat conductivity, shear viscosity and electric conductivity respectively. In the present paper, we will study the color-electric conductivity of the QGP in presence of shear viscosity, which is focused on the connection between the charge transport and the momentum transport. To achieve that goal, we solve the viscous chromohydrodynamic equations which are obtained from the QGP kinetic theory associated with the distribution function modified by shear viscosity. According to the solved color fluctuations of hydrodynamic quantities we obtain the induced color current through which the color-electric conductivity is derived. Then we study viscous effects on the color-electric conductivity. In the viscous chromohydrodynamic approach, the conductivity properties of the QGP are mainly demonstrated by the longitudinal part of the color-electric conductivity. Shear viscosity has an appreciable impact on real and imaginary parts of the color-electric conductivity in some frequency region.

   hep-phCPC(2021)·4 citations
5. 05*

   Dynamic scale anomalous transport in QCD with electromagnetic background

   Mamiya Kawaguchi🇨🇳 · Shinya Matsuzaki🇨🇳 · Xu-Guang Huang🇨🇳

   We discuss phenomenological implications of the anomalous transport induced by the scale anomaly in QCD coupled to an electromagnetic (EM) field, based on a dilaton effective theory. The scale anomalous current emerges in a way perfectly analogous to the conformal transport current induced in a curved spacetime background, or the Nernst current in Dirac and Weyl semimetals -- both current forms are equivalent by a "Weyl transformation". We focus on a spatially homogeneous system of QCD hadron phase, which is expected to be created after the QCD phase transition and thermalization. We find that the EM field can induce a dynamic oscillatory dilaton field which in turn induces the scale anomalous current. As the phenomenological applications, we evaluate the dilepton and diphoton productions induced from the dynamic scale anomalous current, and find that those productions include a characteristic peak structure related to the dynamic oscillatory dilaton, which could be tested in heavy ion collisions. We also briefly discuss the out-of-equilibrium particle production created by a nonadiabatic dilaton oscillation, which happens in a way of the so-called tachyonic preheating mechanism.

   hep-phhep-exhep-thnucl-thJHEP(2020)·10 citations
6. 06*

   Lepton flavor violations in SUSY models for muon $g-2$ with right-handed neutrinos

   Ryo Nagai🇮🇹 · Norimi Yokozaki🇯🇵

   We consider supersymmetric (SUSY) models for the muon $g-2$ anomaly without flavor violating masses at the tree-level. The models can avoid LHC constraints and the vacuum stability constraint in the stau-Higgs potential. Although large flavor violating processes are not induced within the framework of minimal SUSY standard model, once we adopt a seesaw model, sizable lepton flavor violating (LFV) processes such as $\mu \to e\gamma$ and $\mu \to e$ conversion are induced. These LFV processes will be observed at future experiments such as MEG-II, COMET and Mu2e if right-handed neutrinos are heavier than $10^9$ GeV motivated by the successful leptogenesis. This conclusion is somewhat model independent since Higgs doublets are required to have large soft SUSY breaking masses, leading to flavor violations in a slepton sector via neutrino Yukawa interactions.

   hep-phhep-exJHEP(2021)·7 citations
7. 07*

   Analytical models of the Proton Structure Function and the gluon distribution at small x beyond leading order

   Luxmi Machahari🇮🇳 · D. K. Choudhury🇮🇳

   We incorporate the next-to-leading order (NLO) and the next-to-next-to-leading order (NNLO) effects in the models of the Singlet Structure function F_2^S(x,t) and the gluon distribution G(x,t) using DGLAP equations approximated at small x. Analytical solutions both at the next-to leading order (NLO) as well as the next-to-next-to leading order (NNLO) are obtained. We then make comparisons with exact results.

   hep-phBulg.J.Phys.(2026)·1 citation
8. 08*

   Peaks within peaks and the possible two-peak structure of the Pc(4457): the effective field theory perspective

   Fang-Zheng Peng🇨🇳 · Jun-Xu Lu🇨🇳 · Mario Sánchez Sánchez🇫🇷 · Mao-Jun Yan🇨🇳 · Manuel Pavon Valderrama🇨🇳

   The LHCb pentaquarks -- the $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ -- have been theorized to be ${\Sigma }_c\bar{D}$ and ${\Sigma }_c{\bar{D}}^{\ast }$ S-wave molecules. Here we explore the possibility that two of these pentaquarks -- the $P_c(4440)$ and $P_c(4457)$ -- contain in addition a ${\Lambda }_c(2595)\bar{D}$ component in P-wave. We will analyze the effects of this extra channel within two effective field theories: the first one will be a standard contact-range effective field theory and the second one will include the non-diagonal pion dynamics connecting the ${\Sigma }_c{\bar{D}}^{\ast }$ and ${\Lambda }_c(2595)\bar{D}$ channels, which happens to be unusually long-ranged. The impact of the coupled-channel dynamics between the ${\Sigma }_c{\bar{D}}^{\ast }$ and ${\Lambda }_c(2595)\bar{D}$ components is modest at best for the $P_c(4440)$ and $P_c(4457)$, which will remain to be predominantly ${\Sigma }_c{\bar{D}}^{\ast }$ molecules. However, if the quantum numbers of the $P_c(4457)$ are $J^P={\frac{1}{2}}^{-}$, the coupled-channel dynamics is likely to induce the binding of a ${\Lambda }_c(2595)\bar{D}$ S-wave molecule (coupled to ${\Sigma }_c{\bar{D}}^{\ast }$ in P-wave) with $J^P={\frac{1}{2}}^{+}$ and a mass similar to the $P_c(4457)$. If this is the case, the $P_c(4457)$ could actually be a double peak containing two different pentaquark states.

   hep-phhep-exnucl-thPRD(2021)·26 citations
9. 09*

   Probing P- and CP-violation in dark matter interactions

   Riccardo Catena🇸🇪 · Joakim Hagel🇸🇪 · Carlos E. Yaguna🇨🇴

   Discrete symmetries played a central role in elucidating the structure of the weak interactions, and they will probably be equally crucial regarding the interactions of the dark matter (DM) particle -- whose nature remains elusive. In this work we show that signals in future direct detection experiments can be used to test, in a model-independent way, for P- and CP-violation in DM-nucleus interactions. The analysis is performed within the most general effective theory for non-relativistic spin-0 DM-nucleus interactions mediated by the exchange of a heavy particle. Assuming an idealised xenon detector, we calculate the expected number of DM signal events required to reject P and CP invariant DM-nucleus interactions. For a DM mass of 30 GeV (or higher), this number lies between about 10 and 300 DM signal events, depending on how P and CP invariance are modeled. Future direct detection experiments, therefore, have the potential to reveal P- and CP-violation in DM interactions, making a decisive step toward the identification of the DM particle.

   hep-phastro-ph.COJCAP(2021)·1 citation
10. 10*

    Putting SMEFT Fits to Work

    Sally Dawson🇺🇸 · Samuel Homiller🇺🇸 · Samuel D. Lane🇺🇸

    The Standard Model Effective Field Theory (SMEFT) provides a consistent framework for comparing precision measurements at the LHC to the Standard Model. The observation of statistically significant non-zero SMEFT coefficients would correspond to physics beyond the Standard Model (BSM) of some sort. A more difficult question to answer is what, if any, detailed information about the nature of the underlying high scale model can be obtained from these measurements. In this work, we consider the patterns of SMEFT operators present in five example models and discuss the assumptions inherent in using global fits to make BSM conclusions. We find that including renormalization group effects has a significant impact on the interpretation of the results. As a by-product of our study, we present an up-dated global fit to SMEFT coefficients in the Warsaw basis including some next-to-leading order QCD corrections in the SMEFT theory.

    hep-phPRD(2020)·133 citations
11. 11*

    Time-domain properties of electromagnetic signals in a dynamical axion background

    Peter Adshead🇺🇸 · Patrick Draper🇺🇸 · Benjamin Lillard🇺🇸

    Electromagnetic waves in a dynamical axion background exhibit superluminal group velocities at high frequencies and instabilities at low frequencies, altering how photons propagate through space. Local disturbances propagate causally, but unlike in ordinary Maxwell theory, propagation occurs inside as well as on the lightcone. For the unstable modes, the energy density in the electromagnetic field grows exponentially along timelike displacements. In this paper we derive retarded Green functions in axion electrodynamics in various limits and study the time-domain properties of propagating signals.

    hep-phastro-ph.COPRD(2020)·10 citations
12. 12*

    Polarized light-by-light scattering at the CLIC induced by axion-like particles

    S.C. İnan🇹🇷 · A.V. Kisselev🇷🇺

    The light-by-light (LBL) scattering with initial polarized Compton backscattered photons at the CLIC, induced by axion-like particles (ALPs), is investigated. The total cross sections are calculated, assuming CP-even coupling of the pseudoscalar ALP to photons. The 95\% C.L. exclusion region for the ALP mass $m_a$ and its coupling constant $f$ is presented. The results are compared with previously obtained CLIC bounds for the unpolarized case. It is shown that the bounds on $f$ for the polarized beams in the region $m_a=1000\mathrm{GeV}-2000\mathrm{GeV}$, with the collision energy 3000 GeV and integrated luminosity 4000 fb${}^{-1}$, are on average 1.5 times stronger than the bounds for the unpolarized beams. Herewith, our CLIC bounds are stronger than all current exclusion regions for $m_a>80$ GeV. In particular, they are more restrictive than the limits which follow from the ALP-mediated LBL scattering at the LHC.

    hep-phhep-exCPC(2021)·22 citations
13. 13*

    Diffractive $\gamma \gamma$ production in $pp$ collisions at the LHC

    V. P. Goncalves🇧🇷 · D. E. Martins🇧🇷 · M. S. Rangel🇧🇷

    In this letter we estimate the contribution of the double diffractive processes for the diphoton production in $pp$ collisions at the Large Hadron Collider (LHC). The acceptance of the central and forward LHC detectors is taken into account and predictions for the invariant mass, rapidity and, transverse momentum distributions are presented. A comparison with the predictions for the Light -- by -- Light (LbL) scattering and exclusive diphoton production is performed. We demonstrate that the events associated to double diffractive processes can be separated and its study can be used to constrain the behavior of the diffractive parton distribution functions.

    hep-phhep-exEPJC(2020)·5 citations
14. 14*

    Implications of a possible TeV break in the cosmic-ray electron and positron flux

    Yu-Chen Ding🇨🇳 · Nan Li🇨🇳 · Chun-Cheng Wei🇨🇳 · Yue-Liang Wu🇨🇳 · Yu-Feng Zhou🇨🇳

    A TeV spectral break in the total flux of cosmic-ray electrons and positrons (CREs) at which the spectral power index softens from $\sim 3$ to $\sim 4$ has been observed by H.E.S.S. and recently confirmed by DAMPE with a high significance of $6.6\sigma$. Such an observation is apparently inconsistent with the data from other experiments such as Fermi-LAT, AMS-02 and CALET. We perform a global analysis to the latest CRE data including Fermi-LAT, AMS-02, CALET, DAMPE and H.E.S.S. with energy scale uncertainties taken into account to improve the consistency between the data sets. The fit result strongly favors the existence of the break at $\sim 1$ TeV with an even higher statistical significance of $13.3\sigma$. In view of the tentative CRE break, we revisit a number of models of nearby sources, such as a single generic Pulsar Wind Nebula (PWN), known multiple PWNe from the ATNF catalog, and their combinations with either an additional Dark Matter (DM) component or a Supernova Remnant (SNR). We show that the CRE break at $\sim 1$ TeV, together with the known CR positron excess points towards the possibility that the nearby sources should be highly charge asymmetric. Among the models under consideration, the one with a PWN plus SNR is most favored by the current data. The favoured distance and age of the PWN and SNR sources are both within $0.6$ kpc and around $10^5$ yr respectively. Possible candidate sources include PSR J0954-5430, Vela and Monogem ring, etc. We find that for the models under consideration, the additional DM component is either unnecessary, or predicts too much photons in tension with the H.E.S.S. data of $\gamma$-rays from the direction of the Galactic Center. We also show that the current measurement of the anisotropies in the arrival direction of the CRE can be useful in determining the property of the sources.

    ↳ astro-ph.HEhep-phPRD(2021)·17 citations
15. 15*

    Possible octupole deformation of ${}^{208}$Pb and the ultracentral $v_2$ to $v_3$ puzzle

    Patrick Carzon🇺🇸 · Skandaprasad Rao🇺🇸 · Matthew Luzum🇧🇷 · Matthew Sievert🇺🇸 · Jacquelyn Noronha-Hostler🇺🇸

    Recent measurements have established the sensitivity of ultracentral heavy-ion collisions to the deformation parameters of non-spherical nuclei. In the case of ${}^{129}$Xe collisions, a quadrupole deformation of the nuclear profile led to an enhancement of elliptic flow in the most central collisions. In ${}^{208}$Pb collisions a discrepancy exists in similar centralities, where either elliptic flow is over-predicted or triangular flow is under-predicted by hydrodynamic models; this is known as the $v_2$-to-$v_3$ puzzle in ultracentral collisions. Motivated by low-energy nuclear structure calculations, we consider the possibility that ${}^{208}$Pb nuclei could have a pear shape deformation (octupole), which has the effect of increasing triangular flow in central PbPb collisions. Using the recent data from ALICE and ATLAS, we revisit the $v_2$-to-$v_3$ puzzle in ultracentral collisions, including new constraints from recent measurements of the triangular cumulant ratio $v_3\left\{4\right\}/v_3\left\{2\right\}$ and comparing two different hydrodynamic models. We find that, while an octupole deformation would slightly improve the ratio between $v_2$ and $v_3$, it is at the expense of a significantly worse triangular flow cumulant ratio. In fact, the latter observable prefers no octupole deformation, with ${\beta }_3\lesssim 0.0375$ for ${}^{208}$Pb, and is therefore consistent with the expectation for a doubly-magic nucleus even at top collider energies. The $v_2$-to-$v_3$ puzzle remains a challenge for hydrodynamic models.

    ↳ nucl-thhep-phnucl-exPRC(2020)·40 citations
16. 16*

    Nuclear spin-dependent parity-violating effects in light polyatomic molecules

    Yongliang Hao🇳🇱 · Petr Navrátil🇨🇦 · Eric B. Norrgard🇺🇸 · Miroslav Iliaš🇸🇰 · Ephraim Eliav🇮🇱 · Rob G. E. Timmermans🇳🇱 · Victor V. Flambaum🇦🇺 · Anastasia Borschevsky🇳🇱

    Measurements of nuclear spin-dependent parity-violating (NSD-PV) effects provide an excellent opportunity to test nuclear models and to search for physics beyond the Standard Model. Molecules possess closely-spaced states with opposite parity which may be easily tuned to degeneracy to greatly enhance the observed parity-violating effects. A high-sensitivity measurement of NSD-PV effects using light triatomic molecules is in preparation [E. B. Norrgard, et al., Commun. Phys. 2, 77 (2019)]. Importantly, by comparing these measurements in light nuclei with prior and ongoing measurements in heavier systems, the contribution to NSD-PV from $Z^0$-boson exchange between the electrons and the nuclei may be separated from the contribution of the nuclear anapole moment. Furthermore, light triatomic molecules offer the possibility to search for new particles, such as the postulated $Z^{\prime }$ boson. In this work, we detail a sensitive measurement scheme and present high-accuracy molecular and nuclear calculations needed for interpretation of NSD-PV experiments on triatomic molecules composed of light elements Be, Mg, N, and C. The ab initio nuclear structure calculations, performed within the No-Core Shell Model (NCSM) provide a reliable prediction of the magnitude of different contributions to the NSD-PV effects in the four nuclei. These results differ significantly from the predictions of the standard single-particle model and highlight the importance of including many-body effects in such calculations. In order to extract the NSD-PV contributions from measurements, a parity-violating interaction parameter $W_{\text{PV}}$, which depends on molecular structure, needs to be known with high accuracy. We have calculated these parameters for the triatomic molecules of interest using the relativistic coupled-cluster approach.

    ↳ physics.atom-phhep-phnucl-thPRA(2020)·35 citations
17. 17*

    Hadronic vacuum polarization using gradient flow

    Robert V. Harlander🇩🇪 · Fabian Lange🇩🇪 · Tobias Neumann🇺🇸

    The gradient-flow operator product expansion for QCD current correlators including operators up to mass dimension four is calculated through NNLO. This paves an alternative way for efficient lattice evaluations of hadronic vacuum polarization functions. In addition, flow-time evolution equations for flowed composite operators are derived. Their explicit form for the non-trivial dimension-four operators of QCD is given through order ${\alpha }_s^3$.

    ↳ hep-lathep-phJHEP(2020)·27 citations
18. 18*

    Reheating after S-Brane Ekpyrosis

    Robert Brandenberger🇨🇦 · Keshav Dasgupta🇨🇦 · Ziwei Wang🇨🇦

    In recent work, two of us proposed a nonsingular Ekpyrotic cosmology making use of an S-brane which forms at the end of the phase of Ekpyrotic contraction. This S-Brane mediates a transition between contraction and expansion. Graviitational waves passing through the S-Brane acquire a roughly scale-invariant spectrum, and if the S-Brane has zero shear, then a roughly scale-invariant spectrum of cosmological perturbatiions results. Here, we study the production of gauge field fluctuations driven by the decay of the S-Brane, and we show that the reheating process via gauge field production will be efficient, leading to a radiation-dominated expanding phase.

    ↳ hep-thastro-ph.COgr-qchep-phPRD(2020)·29 citations
19. 19*

    The Imprint of Relativistic Particles on the Anisotropies of the Stochastic Gravitational-Wave Background

    Lorenzo Valbusa Dall'Armi🇮🇹 · Angelo Ricciardone🇮🇹 · Nicola Bartolo🇮🇹 · Daniele Bertacca🇮🇹 · Sabino Matarrese🇮🇹

    The Stochastic Gravitational-Wave Background (SGWB) is expected to be a key observable for Gravitational-Wave (GW) interferometry. Its detection will open a new window on early Universe cosmology, on the astrophysics of compact objects and, as shown in this Letter, on the particle physics content of the Universe. In this Letter we show that, besides their effects on the Cosmic Microwave Background (CMB) and on Large Scale Structure (LSS), relativistic particles in the early Universe leave a clear imprint on the anisotropies of the SGWB. In particular we show that a change in the number of decoupled relativistic particles shifts the angular power spectrum of the SGWB, as both the Sachs-Wolfe (SW) and the Integrated Sachs-Wolfe (ISW) terms are affected. Being very large-angle effects, these lead to new testable predictions for future GW interferometers.

    ↳ astro-ph.COgr-qchep-phPRD(2021)·71 citations
20. 20*

    Thermal Field Theory in real-time formalism: concepts and applications for particle decays

    Torbjörn Lundberg🇸🇪 · Roman Pasechnik🇸🇪

    This review represents a detailed and comprehensive discussion of the Thermal Field Theory (TFT) concepts and key results in Yukawa-type theories. We start with a general pedagogical introduction into the TFT in the imaginary- and real-time formulation. As phenomenologically relevant implications, we present a compendium of thermal decay rates for several typical reactions calculated within the framework of the real-time formalism and compared to the imaginary-time results found in the literature. Processes considered here are those of a neutral (pseudo)scalar decaying into two distinct (pseudo)scalars or into a fermion-antifermion pair. These processes are extended from earlier works to include chemical potentials and distinct species in the final state. In addition, a (pseudo)scalar emission off a fermion line is also discussed. These results demonstrate the importance of thermal effects in particle decay observables relevant in many phenomenological applications in systems at high temperatures and densities.

    ↳ hep-thhep-phquant-phEPJA(2021)·32 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.