Fri·Nov 12, 2021Friday·November 12, 2021

1. 01*

   Monte Carlo Event Generator updates, for tau pair events at Belle II energies

   Sw. Banerjee🇺🇸 · D. Biswas🇺🇸 · T. Przedzinski🇵🇱 · Z. Was🇵🇱

   The Monte Carlo for lepton pair production and tau decays consist of KKMC for lepton pair production, tauola for tau lepton decays and photos for radiative corrections in decays. An effort for adaptation of the system for precision data to be collected at Belle II experiment lead to extension of phase space generation modules both in photos and tauola to enable decays and/or radiative corrections of additional light lepton pairs. The phase-space and matrix element parts of the programs are separated, that is why extension to processes where lepton pair is produced through narrow resonances, like dark photon, was straight forward. In the present version of tauola, list of tau decay channels is enriched with multitude of exotic ones, useful for searches of new physics. The hadronic currents parametrizations of main decay channels is prepared for basic simulation in the experiment. The basis for future work on precise fits of hadronic currents including Machine Learning is retained, but development of necessary software solutions is left for the forthcoming years. Presented programs versions are available in stand-alone format from gitlab or through the basf2 system of Belle II software. Official distribution web pages, documenting programs tests, are retained but not necessarily up to the date.

   hep-phhep-exSciPost Phys.Proc.(2025)·22 citations
2. 02*

   Finite volume and magnetic field effects on the two-pion correlation function in relativistic heavy-ion collisions

   Alejandro Ayala🇲🇽 · Santiago Bernal-Langarica🇲🇽 · Cristian Villavicencio🇨🇱

   We study the combined effects of a finite volume and an external magnetic field on the charged two-pion correlation function. For these purposes, we consider a dilute system of pions where the finite volume effects are introduced computing the pion wave functions with rigid boundary conditions in a cylindrical geometry in the presence of a uniform and constant magnetic field. We find that for slow pions, namely, for the case where the average pair momentum is small, the correlation function shows a large distortion, as opposed to the case where the average pair momentum is large. For a finite density system, the intercept of the correlation function is reduced, signaling the increasing importance of the pion ground state contribution. An increasing strength of the magnetic field reduces the importance of the ground state and the intercept becomes closer to 2.

   hep-phnucl-thPRD(2022)·3 citations
3. 03*

   An anthropic solution to the cosmological moduli problem

   Howard Baer🇺🇸 · Vernon Barger🇺🇸 · Robert Wiley Deal🇺🇸

   Light moduli fields, gravitationally coupled scalar fields with no classical potential and which are expected to emerge as remnants from string theory compactification, are dangerous to cosmology in that 1. their late-time decays may disrupt successful Big Bang Nucleosynthesis (BBN), 2. they may decay into gravitino pairs which result in violation of BBN constraints or overproduction of lightest SUSY particles (LSPs, assumed to constitute at least a portion of the dark matter in the universe) and 3. they may decay directly into LSPs, resulting in gross DM overproduction. Together, these constitute the cosmological moduli problem (CMP). The combined effects require lightest modulus mass m_\phi >~10^4 TeV, and if the lightest modulus mass m_\phi is correlated with the SUSY breaking scale m_{3/2}, then the underlying SUSY model would be highly unnatural. We present a solution to the CMP wherein the lightest modulus initial field strength \phi_0 is anthropically selected to be \phi_0\sim 10^{-7}m_P by the requirement that the dark matter-to-baryonic matter ratio be not-too-far removed from its present value so that sufficient baryons are present in the universe to create observers. In this case, instead of dark matter overproduction via neutralino reannihilation at the modulus decay temperature, the neutralinos inherit the reduced moduli number density, thereby gaining accord with the measured dark matter relic density.

   hep-phastro-ph.COJHEAp(2022)·7 citations
4. 04*

   Meta-learning and data augmentation for mass-generalised jet taggers

   Matthew J. Dolan🇦🇺 · Ayodele Ore🇦🇺

   Deep neural networks trained for jet tagging are typically specific to a narrow range of transverse momenta or jet masses. Given the large phase space that the LHC is able to probe, the potential benefit of classifiers that are effective over a wide range of masses or transverse momenta is significant. In this work we benchmark the performance of a number of methods for achieving accurate classification at masses distant from those used in training, with a focus on algorithms that leverage meta-learning. We study the discrimination of jets from boosted $Z^{\prime }$ bosons against a QCD background. We find that a simple data augmentation strategy that standardises the angular scale of jets with different masses is sufficient to produce strong generalisation. The meta-learning algorithms provide only a small improvement in generalisation when combined with this augmentation. We also comment on the relationship between mass generalisation and mass decorrelation, demonstrating that those models which generalise better than the baseline also sculpt the background to a smaller degree.

   hep-phPRD(2022)·8 citations
5. 05*

   Implications of time-dependent inflaton decay on reheating and dark matter production

   Aqeel Ahmed🇩🇪 · Bohdan Grzadkowski🇵🇱 · Anna Socha🇵🇱

   We discuss the production of radiation and dark matter assuming a time-dependent inflaton decay rate during the reheating period. It is shown that the time dependence of the inflaton decay rate can substantially modify the reheating dynamics. As an illustration, a leading interaction between the inflaton $\varphi$ and the Higgs doublet $\mathbf{h}$ of the form $\varphi |\mathbf{h}{|}^2$ was adopted. In the presence of such interaction, the Higgs doublet acquires a $\varphi$-dependent mass which generates vacuum-expectation-value due to inflaton oscillations and breaks the Standard Model gauge symmetry. This leads to a time-dependent inflaton decay rate during the reheating period, and consequently, the production of radiation and dark matter during this period is modified. Regions of the parameter space that describe the observed value of the dark matter abundance were found and compared with the standard case when inflaton the decay rate is constant.

   hep-phPLB(2022)·38 citations
6. 06*

   Applying different angular ordering constraints and $k_t$-factorization approaches to the single inclusive hadron production in the $e^{+}{e}^{-}$ annihilation processes

   M. Modarres🇮🇷 · R. Taghavi🇮🇷

   We study the differential cross section of the single inclusive $e^{+}{e}^{-}$ annihilation to the hadrons via $\gamma$-production, in the different $k_t$-factorization frameworks. In order to take into account the transverse momenta of the incoming partons, for the first time, we apply the Kimber et al (KMR) method to calculate the unintegrated parton fragmentation functions (UFFs) from the ordinary integrated one, i.e., the parton fragmentation functions (FFs), which satisfy the similar DGLAP evolution equations, such as those of parton distribution functions (PDFs). Also, by utilizing the different angular ordering constraints the results corresponding to the Martin et al (MRW) in the leading order (LO) and the next-to-leading-order (NLO) are obtained. The LO sets of DSS library for the input FFs is used. The numerical results are compared with the experimental data in the different energies which are reported by the different collaborations, such as TASSO, AMY, MARK II, CELLO, DELPHI, SLD, ALEPH and Belle with the other QCD+fragmentation models such as Pythia 6.4 and 8.2 parton showers. The behaviors of the normalized differential cross sections and the multiplicity versus the "transverse momentum" ($p_{\perp }$) are discussed. The final results demonstrate that the KMR and MRW UFFs give a good description of data and there is not much significant difference between the above three schemes. On the other hand, our results become closer to the data for the lower values of $p_{\perp }$ and the higher values of center of mass energies.

   hep-phPRD(2021)·2 citations
7. 07*

   QCD $\theta$-vacuum in a Uniform Magnetic Field

   Prabal Adhikari🇺🇸

   We study the $\theta$-vacuum of QCD using two-flavor chiral perturbation theory ($\chi$PT) in the presence of a uniform, background magnetic field calculating the magnetic field-dependent free energy density, the topological density, the topological susceptibility and the fourth cumulant at one-loop order. We find that the topological susceptibility is enhanced by the magnetic field while the fourth topological cumulant is diminished at weak fields and enhanced at larger fields when $\theta =0$. However, in the QCD vacuum with $\theta \ne 0$, the topological susceptibility can be either monotonically enhanced or diminished relative to their $\theta$-vacuum values. The fourth cumulant also exhibits monotonic enhancement or suppression except for regions of $\theta$ near $0$ and $2\pi$, where it is both diminished and enhanced. Finally, the topological density is enhanced for all magnetic fields with its relative shift being identical to the relative shift of the up and down quark condensates in the $\theta$-vacuum.

   hep-phhep-thNPB(2022)·8 citations
8. 08*

   Inclusive Hadroproduction of $P$-wave Heavy Quarkonia in pNRQCD

   Hee Sok Chung🇩🇪

   We compute NRQCD long-distance matrix elements that appear in the inclusive production cross sections of $P$-wave heavy quarkonia in the framework of potential NRQCD. The formalism developed in this work applies to strongly coupled charmonia and bottomonia. This makes possible the determination of color-octet NRQCD long-distance matrix elements without relying on measured cross section data, which has not been possible so far. We obtain results for inclusive production cross sections of ${\chi }_{cJ}$ and ${\chi }_{bJ}$ at the LHC, which are in good agreement with measurements.

   hep-ph0 citations
9. 09*

   Probing the axion-nucleon coupling with the next generation of axion helioscopes

   Luca Di Luzio🇮🇹 · Javier Galan🇪🇸 · Maurizio Giannotti🇺🇸 · Igor G. Irastorza🇪🇸 · Joerg Jaeckel🇩🇪 · Axel Lindner🇩🇪 · Jaime Ruz🇺🇸 · Uwe Schneekloth🇩🇪 · Lukas Sohl🇩🇪 · Lennert J. Thormaehlen🇩🇪 · Julia K. Vogel🇺🇸

   A finite axion-nucleon coupling, nearly unavoidable for QCD axions, leads to the production of axions via the thermal excitation and subsequent de-excitation of Fe-57 isotopes in the sun. We revise the solar bound on this flux adopting the up to date emission rate, and investigate the sensitivity of the proposed International Axion Observatory IAXO and its intermediate stage BabyIAXO to detect these axions. We compare different realistic experimental options and discuss the model dependence of the signal. Already BabyIAXO has sensitivity far beyond previous solar axion searches via the nucleon coupling and IAXO can improve on this by more than an order of magnitude.

   hep-phastro-ph.SRhep-exEPJC(2022)·53 citations
10. 10*

    Neutron star properties with careful parameterization in the (axial)vector meson extended linear sigma model

    Péter Kovács🇭🇺 · János Takátsy🇭🇺 · Jürgen Schaffner-Bielich🇩🇪 · György Wolf🇭🇺

    The existence of quark matter inside the cores of heavy neutron stars is a possibility which can be probed with modern astrophysical observations. We use an (axial)vector meson extended quark-meson model to describe quark matter in the core of neutron stars. We discover that an additional parameter constraint is necessary in the quark model to ensure chiral restoration at high densities. By investigating hybrid star sequences with various parameter sets we show that low sigma meson masses are needed to fulfill the upper radius constraints, and that the maximum mass of stable hybrid stars is only slightly dependent on the parameters of the crossover-type phase transition. Using this observation and results from recent astrophysical measurements a constraint of 2.6 < g_V < 4.3 is set for the constituent quark - vector meson coupling. The effect of a nonzero bag constant is also investigated and we observe that its effect is small for values adopted in previous works.

    ↳ nucl-thhep-phPRD(2022)·22 citations
11. 11*

    Color confinement and restoration of residual local gauge symmetries

    Kei-Ichi Kondo🇯🇵 · Naoki Fukushima🇯🇵

    All colored particles including dynamical quarks and gluons are confined if the color confinement criterion proposed by Kugo and Ojima is satisfied. The criterion was obtained under the gauge fixing of the Lorenz type. However, it was pointed out that the Kugo-Ojima criterion breaks down for the Maximal Abelian gauge, which is quite strange in view of the fact that quark confinement has been verified according to the dual superconductivity caused by magnetic monopole condensations. In order to make a bridge between color confinement due to Kugo and Ojima and the dual superconductor picture for quark confinement, we investigate a generalization of the color confinement criterion to obtain the unified picture for confinement. We show that the restoration of the residual local gauge symmetry which was shown in the Lorenz gauge by Hata to be equivalent to the Kugo-Ojima criterion indeed occurs in the Maximal Abelian gauge for the SU(N) Yang-Mills theory in two-, three- and four-dimensional Euclidean spacetime once the singular topological configurations of gauge fields are taken into account. This result indicates that the color confinement phase is a disordered phase caused by non-trivial topological configurations irrespective of the gauge choice. As a byproduct, we show that the compact U(1) gauge theory can have the disordered confinement phase, while the non-compact U(1) gauge theory has the deconfined Coulomb phase.

    ↳ hep-thhep-lathep-phPTEP(2022)·4 citations
12. 12*

    Pair Production in Real Proper Time and Unitarity Without Borel Ambiguity

    Cihan Pazarbaşı🇹🇷

    The pair production of scalar particles in electromagnetic background fields is analyzed using real proper time formulation of 1-loop effective action. After explaining how real proper time formulation keeps unitarity of the particle creation process in an unambiguous way and discussing the (lack of) pair production in uniform (magnetic) electric backgrounds, we apply these ideas to general electric field backgrounds. Our approach is based on a recursive perturbative expansion of the proper time propagator $U(t)$ and we show how the pair production probabilities can be obtained from its singularities which arises upon a Pade summation of the expansion. We computed the pair production probabilities for general space or time dependent electric fields in locally constant approximation and showed they match with the well-known worldline instanton calculations of pulse and periodic backgrounds. Later, for one dimensional periodic electric and magnetic backgrounds, we showed how the WKB integrals appear in the classical limit. We linked both cases to specific WKB cycles in different spectral regions of the WKB problem and computed the WKB actions by evaluating the WKB integrals as well as by taking phase space integrals directly along Lefschetz thimbles. Finally, we explain the equivalence of our construction with exact WKB method in the classical limit by showing how the WKB cycles precisely contribute to the pair production process which is in complete agreement with our time dependent setting.

    ↳ hep-thhep-ph0 citations
13. 13*

    Nonperturbative excitations in overoccupied gluon plasmas

    Kirill Boguslavski🇦🇹

    Motivated by the early-time dynamics of the quark-gluon plasma in high-energy heavy-ion collisions, we extract gluonic spectral functions of overoccupied gauge theories far from equilibrium using classical-statistical lattice simulations and linear response theory. In 3+1 dimensions we find that the spectral function exhibits quasiparticle excitations at all momenta that are mostly consistent with perturbative hard-thermal loop predictions, while partially showing nonperturbative deviations. In contrast, the structure of excitations in 2+1 dimensions is nontrivial and nonperturbative. These nonperturbative interactions lead to broad excitation peaks in the spectral function, demonstrating the absence of soft quasiparticles in these theories. This also suggests that there may be significant nonperturbative corrections present in systems with large momentum anisotropy, which are relevant to phenomenological applications in heavy-ion collisions.

    ↳ hep-lathep-phnucl-thPoS(2022)·0 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.