Fri·Jan 22, 2021Friday·January 22, 2021

1. 01*

   The LHC Olympics 2020: A Community Challenge for Anomaly Detection in High Energy Physics

   Gregor Kasieczka (ed) · Benjamin Nachman (ed) · David Shih (ed) · Oz Amram · Anders Andreassen · Kees Benkendorfer · Blaz Bortolato · Gustaaf Brooijmans · Florencia Canelli · Jack H. Collins · Biwei Dai · Felipe F. De Freitas and 35 other authors

   A new paradigm for data-driven, model-agnostic new physics searches at colliders is emerging, and aims to leverage recent breakthroughs in anomaly detection and machine learning. In order to develop and benchmark new anomaly detection methods within this framework, it is essential to have standard datasets. To this end, we have created the LHC Olympics 2020, a community challenge accompanied by a set of simulated collider events. Participants in these Olympics have developed their methods using an R&D dataset and then tested them on black boxes: datasets with an unknown anomaly (or not). This paper will review the LHC Olympics 2020 challenge, including an overview of the competition, a description of methods deployed in the competition, lessons learned from the experience, and implications for data analyses with future datasets as well as future colliders.

   hep-phhep-exphysics.data-anRept.Prog.Phys.(2021)·252 citations
2. 02*

   Exclusive dilepton production via timelike Compton scattering in heavy ion collisions

   G. M. Peccini🇧🇷 · L. S. Moriggi🇧🇷 · M. V. T. Machado🇧🇷

   In the present work, $k_T$-factorization formalism is applied to compute the exclusive dilepton production by timelike Compton scattering (TCS) in $eA$, $pA$ and $AA$ collisions. The nuclear effects are investigated considering heavy and light ions. The production cross section in terms of invariant mass and rapidity distribution of the lepton pair is shown. The analysis is done for electron-ion collisions at the Large Hadron-Electron Collider (LHeC), its high-energy upgrade (HE-LHeC) and at the Future Circular Collider (FCC) in lepton-hadron mode. Additionally, ultraperipheral heavy ion collisions at future runs of the Large Hadron Collider (LHC) and at the FCC (hadron-hadron mode) are also considered.

   hep-phhep-exPRD(2021)·16 citations
3. 03*

   On Mass and Matter

   Craig D. Roberts🇨🇳

   The visible Universe is largely characterised by a single mass-scale; namely, the proton mass, $m_p$. Contemporary theory suggests that $m_p$ emerges as a consequence of gluon self-interactions, which are a defining characteristic of quantum chromodynamics (QCD), the theory of strong interactions in the Standard Model. However, the proton is not elementary. Its mass appears as a corollary of other, more basic emergent phenomena latent in the QCD Lagrangian, e.g. generation of nuclear-size gluon and quark mass-scales, and a unique effective charge that may describe QCD interactions at all accessible momentum scales. These remarks are explained herein; and focusing on the distribution amplitudes and functions of $\pi$ and $K$ mesons, promising paths for their empirical verification are elucidated. Connected therewith, in anticipation that production of $J/\psi$-mesons using $\pi$ and $K$ beams can provide access to the gluon distributions in these pseudo-Nambu-Goldstone modes, predictions for all $\pi$ and $K$ distribution functions are provided at the scale $\zeta =m_{J/\psi }$.

   hep-phhep-exhep-latnucl-ex+1AAPPS Bull.(2021)·51 citations
4. 04*

   Kubo formulae for first-order spin hydrodynamics

   Jin Hu🇨🇳

   We derive Kubo formulae for first-order spin hydrodynamics based on non-equilibrium statistical operators method. In first-order spin hydrodynamics, there are two new transport coefficients besides the ordinary ones appearing in first-order viscous hydrodynamics. They emerge due to the incorporation of the spin degree of freedom into fluids and the spin-orbital coupling. Zubarev's non-equilibrium statistical operator method can be well applied to investigate these quantum effects in fluids. The Kubo formulae, based on the method of non-equilibrium statistical operators, are related to equilibrium (imaginary-time) infrared Green's functions, and all the transport coefficients can be determined when the microscopic theory is specified.

   hep-phPRD(2021)·48 citations
5. 05*

   Critical behaviors of the $O(4)$ and $Z(2)$ symmetries in the QCD phase diagram

   Yong-rui Chen🇨🇳 · Rui Wen🇨🇳 · Wei-jie Fu🇨🇳

   In this work we have studied the QCD phase structure and critical dynamics related to the 3-$d$ $O(4)$ and $Z(2)$ symmetry universality classes in the two-flavor quark-meson low energy effective theory within the functional renormalization group approach. We have employed the expansion of Chebyshev polynomials to solve the flow equation for the order-parameter potential. The chiral phase transition line of $O(4)$ symmetry in the chiral limit, and the $Z(2)$ line of critical end points related to the explicit chiral symmetry breaking are depicted in the phase diagram. Various critical exponents related to the order parameter, chiral susceptibilities and correlation lengths have been calculated for the 3-$d$ $O(4)$ and $Z(2)$ universality classes in the phase diagram, respectively. We find that the critical exponents obtained in the computation, where a field-dependent mesonic nontrivial dispersion relation is taken into account, are in quantitative agreement with results from other approaches, e.g., the conformal bootstrap, Monte Carlo simulations and $d=3$ perturbation expansion, etc. Moreover, the size of the critical regime in the QCD phase diagram is found to be very small.

   hep-phPRD(2021)·27 citations
6. 06*

   Open charm mesons and Charmonia in magnetized strange hadronic matter

   Amal Jahan C.S. · Amruta Mishra🇮🇳

   We investigate the in-medium masses of open charm mesons ($D$($D^0$, $D^{+}$), $\bar{D}$($\overline{D^0}$, $D^{-}$), $D_s$(${D_s}^{+}$, ${D_s}^{-}$)) and charmonium states ($J/\psi$, $\psi (3686)$, $\psi (3770)$, ${\chi }_{c0}$, ${\chi }_{c2}$) in strongly magnetized isospin asymmetric strange hadronic matter using a chiral effective model. In the presence of the magnetic field, the number density and scalar density of charged baryons have contributions from Landau energy levels. The mass modifications of open charm mesons arise due to their interactions with nucleons, hyperons, and the scalar fields (the non-strange field $\sigma$, strange field $\zeta$ and isovector field $\delta$) in the presence of the magnetic field. The mass modifications of the charmonium states arise from the variation of dilaton field ($\chi$) in the magnetized medium, which simulates the gluon condensates of QCD. The in-medium mass of open charm mesons and charmonia are observed to decrease with an increase in baryon density, whereas the charged $D^{+}$, $D^{-}$, ${D_s}^{+}$ and ${D_s}^{-}$ mesons have additional positive mass shifts due to Landau quantization in the presence of the magnetic field. The effects of strangeness fraction are found to be more dominant for the $\bar{D}$ mesons as compared to the $D$ mesons. The mass shifts of charmonia are observed to be larger in hyperonic medium compared to the nuclear medium.

   hep-phnucl-thCPC(2022)·10 citations
7. 07*

   Rapidity window dependence of ridge correlations in the glasma

   Donghai Zhang🇨🇳 · Yeyin Zhao🇨🇳 · Mingmei Xu🇨🇳 · Xue Pan🇨🇳 · Yuanfang Wu🇨🇳

   We study ridge correlations of the glasma in pp collisions at $\sqrt{s_{\mathrm{NN}}}=7$ TeV by using the color glass condensate (CGC) formalism. The azimuthal collimation at long range rapidity is intrinsic to glasma dynamics and is reproduced here. When rapidity window enlarges, ridge correlations in two dimensional $\Delta y$-$\Delta \varphi$ distribution and one dimensional $\Delta \varphi$ distribution at long range rapidity gap are enhanced. The enhancements are demonstrated to be the contributions of source gluons. The quantum evolution of the gluons presents unique correlation patterns in differential correlation function. These characters of two gluon correlations open a way of testing the production mechanism from experimental measurements.

   hep-phNPA(2021)·1 citation
8. 08*

   Bound states of WIMP dark matter in Higgs-portal models. Part I. Cross-sections and transition rates

   Ruben Oncala🇫🇷 · Kalliopi Petraki🇫🇷

   We investigate the role of the Higgs \emph{doublet} in the thermal decoupling of multi-TeV dark matter coupled to the Weak interactions of the Standard Model and the Higgs. The Higgs doublet can mediate a long-range force that affects the annihilation processes and binds dark matter into bound states. More importantly, the emission of a Higgs doublet by a pair of dark matter particles can give rise to extremely rapid monopole bound-state formation processes and bound-to-bound transitions. We compute these effects in the unbroken electroweak phase. To this end, we consider the simplest renormalisable fermionic model, consisting of a singlet and a doublet under $S{U}_L(2)$ that are stabilised by a ${\mathbb{Z}}_2$ symmetry, in the regime where the two multiplets coannihilate. In a companion paper, we use the results to show that the formation of metastable bound states via Higgs-doublet emission and their decay decrease the relic density very significantly.

   hep-phJHEP(2021)·21 citations
9. 09*

   Bound states of WIMP dark matter in Higgs-portal models. Part II. Thermal decoupling

   Ruben Oncala🇫🇷 · Kalliopi Petraki🇫🇷

   The Higgs doublet can mediate a long-range interaction between multi-TeV particles coupled to the Weak interactions of the Standard Model, while its emission can lead to very rapid bound-state formation processes and bound-to-bound transitions. Using the rates calculated in a companion paper, here we compute the thermal decoupling of multi-TeV WIMP dark matter coupled to the Higgs, and show that the formation of metastable dark matter bound states via Higgs-doublet emission and their decay decrease the relic density very significantly. This in turn implies that WIMP dark matter may be much heavier than previously anticipated, or conversely that for a given mass, the dark matter couplings to the Higgs may be much lower than previously predicted, thereby altering the dark matter phenomenology. While we focus on a minimal singlet-doublet model in the coannihilation regime, our calculations can be extended to larger multiplets where the effects under consideration are expected to be even more significant.

   hep-phJHEP(2021)·15 citations
10. 10*

    Photoproduction of ${\Lambda }^{\ast }$ and ${\Sigma }^{\ast }$ resonances with $J^P=1/2^{-}$ off the proton

    Sang-Ho Kim🇰🇷 · K. P. Khemchandani🇧🇷 · A. Martinez Torres🇧🇷 · Seung-il Nam🇰🇷 · Atsushi Hosaka🇯🇵

    We study the photoproduction of the $\Lambda (1405)$ and $\Sigma (1400)$ hyperon resonances, the latter of which is not a well established state. We evaluate the $s$-, $t$- and $u$-channel diagrams in the Born approximation by employing the effective Lagrangians. A new ingredient is the inclusion of a nucleon resonance $N^{\ast }(1895)$ that is dynamically generated with predictions for its coupling to the $K\Lambda (1405)$ and $K\Sigma (1400)$ channels. To extend the applicability of the model to energies beyond the threshold region, we consider a Regge model for the $t$-channel $K$- and $K^{\ast }$-exchanges. Our results are in good agreement with the CLAS data available on $\Lambda (1405)$, while for $\Sigma (1400)$ we predict observables for its production. We also provide polarization observables for both hyperon productions, which can be useful in future experimental investigations. The present study provides new information on the nucleon resonance $N^{\ast }(1895)$ which can be an alternative source for generating the hyperon resonances $\Lambda (1405)$ and $\Sigma (1400)$.

    hep-phhep-exnucl-thPRD(2021)·24 citations
11. 11*

    Modular Invariant Dynamics and Fermion Mass Hierarchies around $\tau =i$

    Ferruccio Feruglio🇮🇹 · Valerio Gherardi🇮🇹 · Andrea Romanino🇮🇹 · Arsenii Titov🇪🇸

    We discuss fermion mass hierarchies within modular invariant flavour models. We analyse the neighbourhood of the self-dual point $\tau =i$, where modular invariant theories possess a residual $Z_4$ invariance. In this region the breaking of $Z_4$ can be fully described by the spurion $ϵ\approx \tau -i$, that flips its sign under $Z_4$. Degeneracies or vanishing eigenvalues of fermion mass matrices, forced by the $Z_4$ symmetry at $\tau =i$, are removed by slightly deviating from the self-dual point. Relevant mass ratios are controlled by powers of $|ϵ|$. We present examples where this mechanism is a key ingredient to successfully implement an hierarchical spectrum in the lepton sector, even in the presence of a non-minimal Kähler potential.

    hep-phhep-thJHEP(2021)·134 citations
12. 12*

    PASSAT at Future Neutrino Experiments: Hybrid Beam-Dump-Helioscope Facilities to Probe Light Axion-Like Particles

    P. S. Bhupal Dev🇺🇸 · Doojin Kim🇺🇸 · Kuver Sinha🇺🇸 · Yongchao Zhang🇨🇳

    There are broadly three channels to probe axion-like particles (ALPs) produced in the laboratory: through their subsequent decay to Standard Model (SM) particles, their scattering with SM particles, or their subsequent conversion to photons. Decay and scattering are the most commonly explored channels in beam-dump type experiments, while conversion has typically been utilized by light-shining-through-wall (LSW) experiments. A new class of experiments, dubbed PASSAT (Particle Accelerator helioScopes for Slim Axion-like-particle deTection), has been proposed to make use of the ALP-to-photon conversion in a novel way: ALPs, after being produced in a beam-dump setup, turn into photons in a magnetic field placed near the source. It has been shown that such hybrid beam-dump-helioscope experiments can probe regions of parameter space that have not been investigated by other laboratory-based experiments, hence providing complementary information; in particular, they probe a fundamentally different region than decay or LSW experiments. We propose the implementation of PASSAT in future neutrino experiments, taking a DUNE-like experiment as an example. We demonstrate that the magnetic field in the planned DUNE multi-purpose detector is already capable of probing the ALP-photon coupling down to $g_{a\gamma \gamma }\sim \mathrm{few}\times 10^{-5}$ GeV${}^{-1}$ for ALP masses $m_a\lesssim 10$ eV. The implementation of a CAST or BabyIAXO-like magnet would improve the sensitivity down to $g_{a\gamma \gamma }\sim 10^{-6}$ GeV${}^{-1}$.

    hep-phhep-exPRD(2021)·12 citations
13. 13*

    Quantifying uncertainties in the solar axion flux and their impact on determining axion model parameters

    Sebastian Hoof🇩🇪 · Joerg Jaeckel🇩🇪 · Lennert J. Thormaehlen🇩🇪

    We review the calculation of the solar axion flux from axion-photon and axion-electron interactions and discuss the size of various effects neglected in current calculations. For the Primakoff flux we then explicitly include the partial degeneracy of electrons. We survey the available solar models and opacity codes and develop a publicly available C++/Python code to quantify the associated systematic differences and statistical uncertainties. The number of axions emitted in helioseismological solar models is systematically larger by about 5% compared to photospheric models, while the overall statistical uncertainties in solar models are typically at the percent level in both helioseismological and photospheric models. However, for specific energies, the statistical fluctuations can reach up to about 5% as well. Taking these uncertainties into account, we investigate the ability of the upcoming helioscope IAXO to discriminate KSVZ axion models. Such a discrimination is possible for a number of models, and a discovery of KSVZ axions with high $E/N$ ratios could potentially help to solve the solar abundance problem. We discuss limitations of the axion emission calculations and identify potential improvements, which would help to determine axion model parameters more accurately.

    hep-phastro-ph.SRJCAP(2021)·54 citations
14. 14*

    Semitauonic $b$-hadron decays: A lepton flavor universality laboratory

    Florian U. Bernlochner🇩🇪 · Manuel Franco Sevilla🇺🇸 · Dean J. Robinson🇺🇸 · Guy Wormser🇫🇷

    The study of lepton flavor universality violation (LFUV) in semitauonic $b$-hadron decays has become increasingly important in light of longstanding anomalies in their measured branching fractions, and the very large datasets anticipated from the LHC and Belle II. In this review, we undertake a comprehensive survey of the experimental environments and methodologies for semitauonic LFUV measurements at the $B$-factories and LHCb, along with a concise overview of the theoretical foundations and predictions for a wide range of semileptonic decay observables. We proceed to examine the future prospects to control systematic uncertainties down to the percent level, matching the precision of Standard Model (SM) predictions. Furthermore, we discuss new perspectives and caveats on combinations of the LFUV data and revisit the world averages for the $\mathcal{R}(D^{(\ast )})$ ratios. Here we demonstrate that different treatments for the correlations of uncertainties from $D^{\ast \ast }$ excited states can vary the current $3\sigma$ tension with the SM within a $1\sigma$ range. Prior experimental overestimates of $D^{\ast \ast }\tau \nu$ contributions may further exacerbate this. The precision of future measurements is also estimated; their power to exploit full differential information, and solutions to the inherent difficulties in self-consistent new physics interpretations of LFUV observables, are briefly explored.

    ↳ hep-exhep-phRMP(2022)·113 citations
15. 15*

    Varying Alpha Generalized Dirac-Born-Infeld Models

    V. C. Tavares🇵🇹 · C. J. A. P. Martins🇵🇹

    We study the cosmological consequences of a class of Dirac-Born-Infeld models, and assess their viability as a candidate for the recent acceleration of the Universe. The model includes both the rolling tachyon field and the generalized Chaplygin gas models as particular limits, and phenomenologically each of these provides a possible mechanism for a deviation of the value of the dark energy equation of state from its canonical (cosmological constant) value. The field-dependent potential that is characteristic of the rolling tachyon also leads to variations of the fine-structure constant $\alpha$, implying that the model can be constrained both by standard cosmological probes and by astrophysical measurements of $\alpha$. Our analysis, using the latest available low-redshfit data and local constraints from atomic clock and weak equivalence principle experiments, shows that the two possible deviations of the dark energy equation of state are constrained to be ${\log }_{10}(1+w_0{)}_V<-7.85$ and ${\log }_{10}(1+w_0{)}_C<-0.85$, respectively for the rolling tachyon and Chaplygin components, both being at the $95.4\%$ confidence level (although the latter depends on the choice of priors, in a way that we quantify). Alternatively, the $95.4\%$ confidence level bound on the dimensionless slope of the potential is ${\log }_{10}\lambda <-5.36$. This confirms previous analyses indicating that in these models the potential needs to be extremely flat.

    ↳ astro-ph.COgr-qchep-phPRD(2021)·4 citations
16. 16*

    Tunnelling and dynamical violation of the Null Energy Condition

    Jean Alexandre🇬🇧 · Janos Polonyi🇫🇷

    The Null Energy Condition is considered the most fundamental of the energy conditions, on which several key results, such as the singularity theorems, are based. The Casimir effect is one of the rare equilibrium mechanisms by which it is breached without invoking modified gravity or non-minimal couplings to exotic matter. In this work we propose an independent dynamical mechanism by which it is violated, with the only ingredients being standard (but non-perturbative) QFT and a minimally coupled scalar field in a double-well potential. As for the Casimir effect, we explain why the Averaged Null Energy Condition should not be violated by this mechanism. Nevertheless, the transient behaviour could have profound impacts in Early Universe Cosmology.

    ↳ hep-thgr-qchep-phPRD(2021)·18 citations
17. 17*

    Impact of Dark Photon Emission on Massive Star Evolution and Pre-Supernova Neutrino Signal

    A. Sieverding🇺🇸 · E. Rrapaj🇺🇸 · G. Guo🇹🇼 · Y.-Z. Qian🇺🇸

    We study the effects of additional cooling due to the emission of a dark matter candidate particle, the dark photon, on the final phases of the evolution of a $15M_{\odot }$ star and resulting modifications of the pre-supernova neutrino signal. For a substantial portion of the dark photon parameter space the extra cooling speeds up Si burning, which results in a reduced number of neutrinos emitted during the last day before core collapse. This reduction can be described by a systematic acceleration of the relevant timescales and the results can be estimated semi-analytically in good agreement with the numerical simulations. Outside the semi-analytic regime we find more complicated effects. In a narrow parameter range, low-mass dark photons lead to an increase of the number of emitted neutrinos because of additional shell burning episodes that delay core collapse. Furthermore, relatively strong couplings produce a thermonuclear runaway during O burning, which could result in a complete disruption of the star but requires more detailed simulations to determine the outcome. Our results show that pre-supernova neutrino signals are a potential probe of the dark photon parameter space.

    ↳ astro-ph.SRhep-phApJ(2021)·5 citations
18. 18*

    Physics reach of a low threshold scintillating argon bubble chamber in coherent elastic neutrino-nucleus scattering reactor experiments

    L. J. Flores🇲🇽 · Eduardo Peinado🇲🇽 · E. Alfonso-Pita🇲🇽 · K. Allen🇺🇸 · M. Baker🇺🇸 · E. Behnke🇺🇸 · M. Bressler🇺🇸 · K. Clark🇨🇦 · R. Coppejans🇺🇸 · C. Cripe🇺🇸 · M. Crisler🇺🇸 · C. E. Dahl🇺🇸 and 22 other authors

    The physics reach of a low threshold (100 eV) scintillating argon bubble chamber sensitive to Coherent Elastic neutrino-Nucleus Scattering (CE$\nu$NS) from reactor neutrinos is studied. The sensitivity to the weak mixing angle, neutrino magnetic moment, and a light $Z^{\prime }$ gauge boson mediator are analyzed. A Monte Carlo simulation of the backgrounds is performed to assess their contribution to the signal. The analysis shows that world-leading sensitivities are achieved with a one-year exposure for a 10 kg chamber at 3 m from a 1 MW${}_{th}$ research reactor or a 100 kg chamber at 30 m from a 2000 MW${}_{th}$ power reactor. Such a detector has the potential to become the leading technology to study CE$\nu$NS using nuclear reactors.

    ↳ hep-exhep-phnucl-exphysics.ins-detPRD(2021)·59 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.