Mon·May 31, 2021Monday·May 31, 2021

1. 01*

   Drell-Yan angular lepton distributions at small $x$ from TMD factorization

   Ian Balitsky🇺🇸

   The Drell-Yan process is studied in the framework of TMD factorization in the Sudakov region $s\gg Q^2\gg q_{\perp }^2$ corresponding to recent LHC experiments with $Q^2$ of order of mass of Z-boson and transverse momentum of DY pair $\sim$ few tens GeV. The DY hadronic tensors are expressed in terms of quark and quark-gluon TMDs with $\frac{1}{Q^2}$ and $\frac{1}{N_c^2}$ accuracy. It is demonstrated that in the leading order in $N_c$ the higher-twist quark-quark-gluon TMDs reduce to leading-twist TMDs due to QCD equation of motion. The resulting hadronic tensors depend on two leading-twist TMDs: $f_1$ responsible for total DY cross section, and Boer-Mulders function $h_1^{\perp }$. The corresponding qualitative and semi-quantitative predictions seem to agree with LHC data on five angular coefficients $A_0-A_4$ of DY pair production. The remaining three coefficients $A_5-A_7$ are determined by quark-quark-gluon TMDs multiplied by extra $\frac{1}{N_c}$ so they appear to be relatively small in accordance with LHC results.

   hep-phJHEP(2021)·21 citations
2. 02*

   Detecting Chiral Magnetic Effect via Deep Learning

   Yuan-Sheng Zhao🇨🇳 · Lingxiao Wang🇩🇪 · Kai Zhou🇩🇪 · Xu-Guang Huang🇨🇳

   The search of chiral magnetic effect (CME) in heavy-ion collisions has attracted long-term attentions. Multiple observables have been proposed but all suffer from obstacles due to large background contaminations. In this Letter, we construct an observable-independent CME-meter based on a deep convolutional neural network. After trained over data set generated by a multiphase transport model, the CME-meter shows high accuracy in recognizing the CME-featured charge separation from the final-state pion spectra. It also exhibits remarkable robustness to diverse conditions including different collision energies, centralities, and elliptic flow backgrounds. In a transfer learning manner, the CME-meter is validated in isobaric collision systems, showing good transferability among different colliding systems. Based on variational approaches, we utilize the DeepDream method to derive the most responsive CME-spectra that demonstrates the physical contents the machine learns.

   hep-phnucl-thPRC(2022)·25 citations
3. 03*

   New physics searches at the ILC positron and electron beam dumps

   Kento Asai🇯🇵 · Sho Iwamoto🇭🇺 · Yasuhito Sakaki🇯🇵 · Daiki Ueda🇯🇵

   We study capability of the ILC beam dump experiment to search for new physics, comparing the performance of the electron and positron beam dumps. The dark photon, axion-like particles, and light scalar bosons are considered as new physics scenarios, where all the important production mechanisms are included: electron-positron pair-annihilation, Primakoff process, and bremsstrahlung productions. We find that the ILC beam dump experiment has higher sensitivity than past beam dump experiments, with the positron beam dump having slightly better performance for new physics particles which are produced by the electron-positron pair-annihilation.

   hep-phhep-exhep-thJHEP(2021)·35 citations
4. 04*

   Higher-Energy Standard Model from the Gauge Group Contraction

   N.A. Gromov🇷🇺

   The evolution of properties and interactions of elementary particles is described, beginning with the Planck scale of $10^{19}$ GeV. The description is based on the hypothesis that high-temperature (high-energy) limit of the Standard Model is generated by the gauge group contraction. In the infinite-temperature limit, properties of particles fundamentally change: all particles lose their masses, only massless neutral $Z$ bosons and $u$ quarks together with neutrinos and photons survive. Weak interactions become long-range ones and are generated by neutral currents. Quarks have only one color degree of freedom.

   hep-phhep-thPhys.Part.Nucl.(2020)·4 citations
5. 05*

   Dark leptophilic scalar with the updated muon $g-2$ anomaly

   Lian-Bao Jia🇨🇳

   The muon $g-2$ anomaly was strengthened by recent experimental results at Fermilab, which may be signatures of new physics. A scenario of leptophilic scalar ${\varphi }_L$ accounting for the muon $g-2$ anomaly is investigated in this paper. Though a light ${\varphi }_L$ mainly decaying into standard model (SM) particles has been excluded by experiments, a dark leptophilic scalar ${\varphi }_L$ predominantly decaying into invisible fermionic dark matter (DM) $\chi \bar{\chi }$ is still allowed. Considering the decay mode ${\varphi }_L\to \chi \bar{\chi }$ opened (here $m_{{\varphi }_L}=3m_{\chi }$), the coupling preferred by the muon $g-2$ and the ${\varphi }_L-\chi$ coupling are derived. The light/heavy ${\varphi }_L$ (roughly 1 GeV as a benchmark value) can be tested by future experiments via DM/SM decay modes, and ${\varphi }_L$'s contribution to the anomalous magnetic moment of tau lepton could be investigated at lepton colliders. The search of $\chi$ via $\chi -$electron scattering in DM direct detection is not sensitive due to a tiny ${\varphi }_L-$electron coupling, especially for $m_{\chi }\gtrsim m_{\mu }$.

   hep-phEPJC(2022)·9 citations
6. 06*

   Heavy neutral leptons in effective field theory and the high-luminosity LHC

   Giovanna Cottin🇨🇱 · Juan Carlos Helo🇨🇱 · Martin Hirsch🇪🇸 · Arsenii Titov🇪🇸 · Zeren Simon Wang🇹🇼

   Heavy neutral leptons (HNLs) with masses around the electroweak scale are expected to be rather long-lived particles, as a result of the observed smallness of the active neutrino masses. In this work, we study long-lived HNLs in $N_R$SMEFT, a Standard Model (SM) extension with singlet fermions to which we add non-renormalizable operators up to dimension-6. Operators which contain two HNLs can lead to a sizable enhancement of the production cross sections, compared to the minimal case where HNLs are produced only via their mixing with the SM neutrinos. We calculate the expected sensitivities for the ATLAS detector and the future far-detector experiments: AL3X, ANUBIS, CODEX-b, FASER, MATHUSLA, and MoEDAL-MAPP in this setup. The sensitive ranges of the HNL mass and of the active-heavy mixing angle are much larger than those in the minimal case. We study both, Dirac and Majorana, HNLs and discuss how the two cases actually differ phenomenologically, for HNL masses above roughly 100 GeV.

   hep-phhep-exJHEP(2021)·63 citations
7. 07*

   Vacuum birefringence at x-ray free-electron lasers

   Felix Karbstein🇩🇪 · Chantal Sundqvist🇩🇪 · Kai S. Schulze🇩🇪 · Ingo Uschmann🇩🇪 · Holger Gies🇩🇪 · Gerhard G. Paulus🇩🇪

   We study the perspectives of measuring the phenomenon of vacuum birefringence predicted by quantum electrodynamics using an x-ray free-electron laser (XFEL) alone. We devise an experimental scheme allowing the XFEL beam to collide with itself under a finite angle, and thus act as both pump and probe field for the effect. The signature of vacuum birefringence is encoded in polarization-flipped signal photons to be detected with high-purity x-ray polarimetry. Our findings for idealized scenarios underline that the discovery potential of solely XFEL-based setups can be comparable to those involving optical high-intensity lasers. For currently achievable scenarios, we identify several key details of the x-ray optical ingredients that exert a strong influence on the magnitude of the desired signatures.

   hep-phphysics.opticsquant-phNew J.Phys.(2021)·40 citations
8. 08*

   Sudakov resummation from the BFKL evolution

   Maxim Nefedov🇷🇺

   The Leding-Logarithmic (LL) gluon Sudakov formfactor is derived from rapidity-ordered BFKL evolution with longitudinal-momentum conservation. This derivation further clarifies the relation between High-Energy and TMD-factorizations and can be extended beyond LL-approximation as well.

   hep-phPRD(2021)·30 citations
9. 09*

   Differential Heavy Quark Distributions and Correlations in Longitudinally Polarized Deep-Inelastic Scattering

   Felix Hekhorn🇮🇹 · Marco Stratmann🇩🇪

   We present a first calculation of the heavy flavor contribution to the longitudinally polarized deep-inelastic scattering structure function $g_1^Q$, differential in the transverse momentum or the rapidity of the observed heavy quark $Q$ or antiquark $\overline{Q}$. All results are obtained at next-to-leading order accuracy in QCD within the framework of a newly developed parton-level Monte Carlo generator that also allows one to study observables associated with the produced heavy quark pair such as its invariant mass distribution or its correlation in azimuthal angle. First phenomenological studies are carried out for various heavy quark distributions in a kinematic regime relevant for a future Electron-Ion Collider with a particular emphasis on the expected size of the corresponding double-spin asymmetries and their sensitivity to the still poorly constrained helicity gluon distribution. Theoretical uncertainties associated with the choice of the factorization scale are discussed for selected observables.

   hep-phPRD(2021)·3 citations
10. 10*

    First Constraints on Nuclear Coupling of Axionlike Particles from the Binary Neutron Star Gravitational Wave Event GW170817

    Jun Zhang🇬🇧 · Zhenwei Lyu🇨🇦 · Junwu Huang🇨🇦 · Matthew C. Johnson🇨🇦 · Laura Sagunski🇩🇪 · Mairi Sakellariadou🇬🇧 · Huan Yang🇨🇦

    Light axion fields, if they exist, can be sourced by neutron stars due to their coupling to nuclear matter, and play a role in binary neutron star mergers. We report on a search for such axions by analysing the gravitational waves from the binary neutron star inspiral GW170817. We find no evidence of axions in the sampled parameter space. The null result allows us to impose constraints on axions with masses below $10^{-11}\mathrm{eV}$ by excluding the ones with decay constants ranging from $1.6\times 10^{16}\mathrm{GeV}$ to $10^{18}\mathrm{GeV}$ at $3\sigma$ confidence level. Our analysis provides the first constraints on axions from neutron star inspirals, and rules out a large region in parameter space that has not been probed by the existing experiments.

    hep-phastro-ph.HEgr-qchep-thPRL(2021)·109 citations
11. 11*

    What is the scale of new physics behind the muon $g-2$?

    Lukas Allwicher🇨🇭 · Luca Di Luzio🇮🇹 · Marco Fedele🇩🇪 · Federico Mescia🇪🇸 · Marco Nardecchia🇮🇹

    We study the constraints imposed by perturbative unitarity on the new physics interpretation of the muon $g-2$ anomaly. Within a Standard Model Effective Field Theory (SMEFT) approach, we find that scattering amplitudes sourced by effective operators saturate perturbative unitarity at about 1 PeV. This corresponds to the highest energy scale that needs to be probed in order to resolve the new physics origin of the muon $g-2$ anomaly. On the other hand, simplified models (e.g.~scalar-fermion Yukawa theories) in which renormalizable couplings are pushed to the boundary of perturbativity still imply new on-shell states below 200 TeV. We finally suggest that the highest new physics scale responsible for the anomalous effect can be reached in non-renormalizable models at the PeV scale.

    hep-phhep-exhep-thPRD(2021)·36 citations
12. 12*

    Z-portal Continuum Dark Matter

    Csaba Csáki🇺🇸 · Sungwoo Hong🇺🇸 · Gowri Kurup🇺🇸 · Seung J. Lee🇰🇷 · Maxim Perelstein🇺🇸 · Wei Xue🇺🇸

    We examine the possibility that dark matter (DM) consists of a gapped continuum, rather than ordinary particles. A Weakly-Interacting Continuum (WIC) model, coupled to the Standard Model via a Z-portal, provides an explicit realization of this idea. The thermal DM relic density in this model is naturally consistent with observations, providing a continuum counterpart of the "WIMP miracle". Direct detection cross sections are strongly suppressed compared to ordinary Z-portal WIMP, thanks to a unique effect of the continuum kinematics. Continuum DM states decay throughout the history of the universe, and observations of cosmic microwave background place constraints on potential late decays. Production of WICs at colliders can provide a striking cascade-decay signature. We show that a simple Z-portal WIC model provides a fully viable DM candidate consistent with all current experimental constraints.

    hep-phastro-ph.COPRL(2022)·21 citations
13. 13*

    The Dark Machines Anomaly Score Challenge: Benchmark Data and Model Independent Event Classification for the Large Hadron Collider

    T. Aarrestad🇨🇭 · M. van Beekveld🇬🇧 · M. Bona🇬🇧 · A. Boveia🇺🇸 · S. Caron🇳🇱 · J. Davies🇬🇧 · A. De Simone🇮🇹 · C. Doglioni🇸🇪 · J.M. Duarte🇺🇸 · A. Farbin🇺🇸 · H. Gupta🇺🇸 · L. Hendriks🇳🇱 and 27 other authors

    We describe the outcome of a data challenge conducted as part of the Dark Machines Initiative and the Les Houches 2019 workshop on Physics at TeV colliders. The challenged aims at detecting signals of new physics at the LHC using unsupervised machine learning algorithms. First, we propose how an anomaly score could be implemented to define model-independent signal regions in LHC searches. We define and describe a large benchmark dataset, consisting of >1 Billion simulated LHC events corresponding to $10{\mathrm{fb}}^{-1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV. We then review a wide range of anomaly detection and density estimation algorithms, developed in the context of the data challenge, and we measure their performance in a set of realistic analysis environments. We draw a number of useful conclusions that will aid the development of unsupervised new physics searches during the third run of the LHC, and provide our benchmark dataset for future studies at https://www.phenoMLdata.org. Code to reproduce the analysis is provided at https://github.com/bostdiek/DarkMachines-UnsupervisedChallenge.

    hep-phhep-exphysics.data-anstat.MLSciPost Phys.(2022)·148 citations
14. 14*

    Scalar Leptoquarks, Baryon Number Violation and Pati-Salam Symmetry

    Clara Murgui🇺🇸 · Mark B. Wise🇺🇸

    One or more scalar leptoquarks with masses around a few TeV may provide a solution to some of the flavor anomalies that have been observed. We discuss the impact of such new degrees on baryon number violation when the theory is embedded in a Pati-Salam model. The Pati-Salam embedding can suppress renormalizable and dimension-five baryon number violation in some cases. Our work extends the results of Assad, Grinstein, and Fornal who considered the same issue for vector leptoquarks.

    hep-phhep-thPRD(2021)·24 citations
15. 15*

    Nonclassicality of axion-like dark matter through gravitational self-interactions

    Michael Kopp🇸🇪 · Vasileios Fragkos🇸🇪 · Igor Pikovski🇸🇪

    Axion-like particles (ALPs) are promising dark matter candidates. They are typically described by a classical field, motivated by large phase space occupation numbers. Here we show that such a description is accompanied by a quantum effect: squeezing due to gravitational self-interactions. For a typical QCD axion today, the onset of squeezing is reached on $\mu \mathrm{s}$-scales and grows over millennia. Thus within the usual models based on the classical Schrödinger-Poisson equation, a type of Gross-Pitaevskii equation, any viable ALP is nonclassical. We also show that squeezing may be relevant on the scales of other self-gravitating systems such as galactic haloes, or solitonic cores. Conversely, our results highlight the incompleteness and limitations of the classical single field description of ALPs.

    ↳ astro-ph.COcond-mat.otherhep-phquant-phPRD(2022)·15 citations
16. 16*

    Hyperon Polarization from the Vortical Fluid in Low Energy Nuclear Collisions

    Yu Guo🇨🇳 · Jinfeng Liao🇺🇸 · Enke Wang🇨🇳 · Hongxi Xing🇨🇳 · Hui Zhang🇨🇳

    In 2017, STAR Collaboration reported the measurements of hyperon global polarization in heavy ion collisions, suggesting the subatomic fireball fluid created in these collisions as the most vortical fluid. There remains the interesting question: at which beam energy the truly most vortical fluid will be located. In this work we perform a systematic study on the beam energy dependence of hyperon global polarization phenomenon, especially in the interesting $\hat{O}(1\sim 10)\mathrm{GeV}$ region. We find a non-monotonic trend, with the global polarization to first increase and then decrease when beam energy is lowered from $27\mathrm{GeV}$ down to $3\mathrm{GeV}$. The maximum polarization signal has been identified around $\sqrt{s_{NN}}=7.7\mathrm{GeV}$, where the heavy ion collisions presumably create the most vortical fluid. Detailed experimental measurements in the $\hat{O}(1\sim 10)\mathrm{GeV}$ beam energy region are expected to test the prediction very soon.

    ↳ nucl-thhep-phnucl-exPRC(2021)·57 citations
17. 17*

    Baryon number in proton-proton and proton-nucleus high energy collisions

    Marek Jeżabek🇵🇱 · Andrzej Rybicki🇵🇱

    New analyses of baryon spectra in proton-proton and proton-carbon collisions at ${\sqrt{s}}_{{}_{\mathrm{NN}}}=17.3$ GeV, made in the framework of two phenomenological models are presented. The first model in question is the classic Dual Parton Model by Capella and Tran Thanh Van, the second is the Gluon Exchange Model very recently proposed by the authors. For both studies, the usage of modern experimental data from the CERN SPS eliminates several of the most important limitations inherent to earlier studies of this type. In both studies, the standard mechanism of baryon stopping with preservation of the diquark, proposed by Capella and Tran Thanh Van fails to describe the distribution of non-strange baryons in collisions of the projectile proton with {\em more than one} nucleon from the carbon target obtained from experimental data, and the upper limit for the contribution of this mechanism can be established. In both cases, the conclusion is that the projectile diquark must be very often disintegrated. This opens new diagrams not available in proton-proton collisions which lead to the transport of baryon number over long distances in rapidity. The present limitations, and possibility of improvement in both approaches are discussed. The implications of our findings for new measurements are addressed, in particular using antiproton beams.

    ↳ nucl-thhep-phEur.Phys.J.Plus(2021)·9 citations
18. 18*

    Standard Model QCD with jets and photons at CMS and ATLAS

    Henning Kirschenmann (for the ATLAS and CMS Collaborations)🇫🇮

    Recent measurements performed by the ATLAS and CMS collaborations on the Run 2 dataset are testing QCD with unprecedented precision. The wealth of data, an ever-improving experimental understanding of jets and photons, and novel measurements of jet substructure enable an improved understanding.

    ↳ hep-exhep-ph0 citations
19. 19*

    Vacuum Radiation in $z=2$ Lifshitz QED

    R. Bufalo🇧🇷 · T. Cardoso e Bufalo🇧🇷

    We discuss in this paper the vacuum Cherenkov radiation in the $z=2$ Lifshitz electrodynamics. The improved ultraviolet behavior, in terms of higher spatial derivatives, and the renormalizable couplings, due to the time-space anisotropic scaling, present in the Lifshitz setting are extremely important in fulfilling the physical constraints in order to this vacuum process to happen. We evaluate in details the instantaneous rate of energy loss for a charge, and also analyze the emission of very soft photons in this framework.

    ↳ hep-thhep-phPRD(2021)·3 citations
20. 20*

    Updated cosmological constraints on Macroscopic Dark Matter

    Luca Caloni🇮🇹 · Martina Gerbino🇮🇹 · Massimiliano Lattanzi🇮🇹

    We revise the cosmological phenomenology of Macroscopic Dark Matter (MDM) candidates, also commonly dubbed as Macros. A possible signature of MDM is the capture of baryons from the cosmological plasma in the pre-recombination epoch, with the consequent injection of high-energy photons in the baryon-photon plasma. By keeping a phenomenological approach, we consider two broad classes of MDM in which Macros are composed either of ordinary matter or antimatter. In both scenarios, we also analyze the impact of a non-vanishing electric charge carried by Macros. We derive constraints on the Macro parameter space from three cosmological processes: the change in the baryon density between the end of the Big Bang Nucleosynthesis (BBN) and the Cosmic Microwave Background (CMB) decoupling, the production of spectral distortions in the CMB and the kinetic coupling between charged MDM and baryons at the time of recombination. In the case of neutral Macros we find that the tightest constraints are set by the baryon density condition in most of the parameter space. For Macros composed of ordinary matter and with binding energy $I$, this leads to the following bound on the reduced cross-section: ${\sigma }_X/M_X\lesssim 6.8\cdot 10^{-7}{\left(I/\mathrm{MeV}\right)}^{-1.56}{\text{cm}}^2{\text{g}}^{-1}$. Charged Macros with surface potential $V_X$, instead, are mainly constrained by the tight coupling with baryons, resulting in ${\sigma }_X/M_X\lesssim 2\cdot 10^{-11}{\left(|V_X|/\mathrm{MeV}\right)}^{-2}{\text{cm}}^2{\text{g}}^{-1}$. Finally, we show that future CMB spectral distortions experiments, like PIXIE and SuperPIXIE, would have the sensitivity to probe larger regions of the parameter space: this would allow either for a possible evidence or for an improvement of the current bounds on Macros as dark matter candidates.

    ↳ astro-ph.COhep-phJCAP(2021)·8 citations
21. 21*

    Quantum Optimisation of Complex Systems with a Quantum Annealer

    Steve Abel🇬🇧 · Andrew Blance🇬🇧 · Michael Spannowsky🇬🇧

    We perform an in-depth comparison of quantum annealing with several classical optimisation techniques, namely thermal annealing, Nelder-Mead, and gradient descent. We begin with a direct study of the 2D Ising model on a quantum annealer, and compare its properties directly with those of the thermal 2D Ising model. These properties include an Ising-like phase transition that can be induced by either a change in 'quantum-ness' of the theory, or by a scaling the Ising couplings up or down. This behaviour is in accord with what is expected from the physical understanding of the quantum system. We then go on to demonstrate the efficacy of the quantum annealer at minimising several increasingly hard two dimensional potentials. For all the potentials we find the general behaviour that Nelder-Mead and gradient descent methods are very susceptible to becoming trapped in false minima, while the thermal anneal method is somewhat better at discovering the true minimum. However, and despite current limitations on its size, the quantum annealer performs a minimisation very markedly better than any of these classical techniques. A quantum anneal can be designed so that the system almost never gets trapped in a false minimum, and rapidly and successfully minimises the potentials.

    ↳ quant-phcond-mat.stat-mechcs.LGhep-ph+1PRA(2022)·33 citations
22. 22*

    Post-Newtonian Gravitational and Scalar Waves in Scalar-Gauss-Bonnet Gravity

    Banafsheh Shiralilou🇳🇱 · Tanja Hinderer🇳🇱 · Samaya Nissanke🇳🇱 · Néstor Ortiz🇲🇽 · Helvi Witek🇺🇸

    Gravitational waves emitted by black hole binary inspiral and mergers enable unprecedented strong-field tests of gravity, requiring accurate theoretical modelling of the expected signals in extensions of General Relativity. In this paper we model the gravitational wave emission of inspiraling binaries in scalar Gauss-Bonnet gravity theories. Going beyond the weak-coupling approximation, we derive the gravitational waveform to first post-Newtonian order beyond the quadrupole approximation and calculate new contributions from nonlinear curvature terms. We quantify the effect of these terms and provide ready-to-implement gravitational wave and scalar waveforms as well as the Fourier domain phase for quasi-circular binaries. We also perform a parameter space study, which indicates that the values of black hole scalar charges play a crucial role in the detectability of deviation from General Relativity. We also compare the scalar waveforms to numerical relativity simulations to assess the impact of the relativistic corrections to the scalar radiation. Our results provide important foundations for future precision tests of gravity.

    ↳ gr-qcastro-ph.HEhep-phhep-thClass.Quant.Grav.(2022)·124 citations
23. 23*

    Potential applications of modular representation theory to quantum mechanics

    Robert A. Wilson🇬🇧

    There is a unique finite group that lies inside the 2-dimensional unitary group but not in the special unitary group, and maps by the symmetric square to an irreducible subgroup of the 3-dimensional real special orthogonal group. In an earlier paper I showed how the representation theory of this group over the real numbers gives rise to much of the structure of the standard model of particle physics, but with a number of added twists. In this theory the group is quantised, but the representations are not. In this paper I consider how a quantisation of the representations might lead to a more fundamental theory.

    ↳ math.GRhep-ph7 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.