Thu·Dec 3, 2020Thursday·December 3, 2020

1. 01*

   Searching for odderon exchange in exclusive $pp\to pp\varphi$ and $pp\to pp\varphi \varphi$ reactions at the LHC

   Piotr Lebiedowicz🇵🇱 · Otto Nachtmann🇩🇪 · Antoni Szczurek🇵🇱

   The possibility to use the exclusive $pp\to pp\varphi$ and $pp\to pp\varphi \varphi$ reactions in identifying the odderon exchange is discussed. So far there is no unambiguous experimental evidence for the odderon, the charge conjugation $C=-1$ counterpart of the $C=+1$ pomeron. Recently proposed tensor-pomeron and vector-odderon model for soft high-energy reactions is applied. For the $pp\to pp\varphi$ reaction at high energies the photon-pomeron fusion is the dominant process and the odderon-pomeron fusion is an interesting alternative. Adding odderon exchange improves considerably description of the proton-proton angular correlations measured by the WA102 collaboration. The $pp\to pp\varphi \varphi$ process via pomeron-pomeron fusion is advantageous one as here the odderon does not couple to protons. The observation of large $M_{\varphi \varphi }$ and the rapidity difference $Y_{\varphi \varphi }$ seems well suited to identify odderon exchange. Comparisons with data from the WA102 experiment are made and predictions for LHC experiments are given.

   hep-phhep-exPoS(2021)·0 citations
2. 02*

   Tensor decomposition for bosonic and fermionic scattering amplitudes

   Tiziano Peraro🇮🇹 · Lorenzo Tancredi🇬🇧

   In this paper, we elaborate on a method to decompose multiloop multileg scattering amplitudes into Lorentz-invariant form factors, which exploits the simplifications that arise from considering four-dimensional external states. We propose a simple and general approach that applies to both fermionic and bosonic amplitudes and allows us to identify a minimal number of physically relevant form factors, which can be related one-to-one to the independent helicity amplitudes. We discuss explicitly its applicability to various four- and five-point scattering amplitudes relevant for LHC physics.

   hep-phhep-thPRD(2021)·100 citations
3. 03*

   Direct Photons from Hot Quark Matter in Renormalized Finite-Time-Path QED

   Ivan Dadić🇭🇷 · Dubravko Klabučar🇭🇷 · Domagoj Kuić🇭🇷

   Within the finite-time-path out-of-equilibrium quantum field theory (QFT), we calculate direct photon emission from early stages of heavy ion collisions, from a narrow window, in which uncertainty relations are still important and they provide a new mechanism for production of photons. The basic difference with respect to earlier calculations, leading to diverging results, is that we use renormalized QED of quarks and photons. Our result is a finite contribution that is consistent with uncertainty relations.

   hep-phhep-thParticles(2020)·3 citations
4. 04*

   Equivariant Energy Flow Networks for Jet Tagging

   Matthew J. Dolan🇦🇺 · Ayodele Ore🇦🇺

   Jet tagging techniques that make use of deep learning show great potential for improving physics analyses at colliders. One such method is the Energy Flow Network (EFN) - a recently introduced neural network architecture that represents jets as permutation-invariant sets of particle momenta while maintaining infrared and collinear safety. We develop a variant of the Energy Flow Network architecture based on the Deep Sets formalism, incorporating permutation-equivariant layers. We derive conditions under which infrared and collinear safety can be maintained, and study the performance of these networks on the canonical example of W-boson tagging. We find that equivariant Energy Flow Networks have similar performance to Particle Flow Networks, which are superior to standard EFNs. However, equivariant Particle Flow Networks suffer from convergence and overfitting issues. Finally, we study how equivariant networks sculpt the jet mass and provide some initial results on decorrelation using planing.

   hep-phPRD(2021)·46 citations
5. 05*

   Chiral phase transition inside a rotating cylinder within the Nambu--Jona-Lasinio model

   Zheng Zhang🇨🇳 · Chao Shi🇨🇳 · Xiao-Tao He🇨🇳 · Xiaofeng Luo🇨🇳 · Hong-Shi Zong🇨🇳

   We study the chiral phase transition inside a rotating cylinder within the framework of the Namb--Jona-Lasinio model. A spectral boundary condition is imposed to avoid faster than light. We investigate how the geometry of the cylinder and rotation influence the chiral phase transition at finite temperature and chemical potential. The inhomogeneous effects caused by the finite size and rotation are also taken into account. It is found that finite size will reduce the chiral transition temperature and raises the chiral transition chemical potential, while the rotation reduces both the chiral transition temperature and chemical potential. In addition, we discuss the implications of our results in heavy-ion collisions and equation of states of neutron star.

   hep-phnucl-thPRD(2020)·23 citations
6. 06*

   Determination of the possible quantum numbers for the newly observed ${\Xi }_b(6227{)}^0$ state

   K. Azizi🇮🇷 · Y. Sarac🇹🇷 · H. Sundu🇹🇷

   The LHCb Collaboration recently reported the observation of a new excited bottom baryon ${\Xi }_b(6227{)}^0$ and announced an improvement in the measurements related to the previously observed ${\Xi }_b(6227{)}^{-}$ state. We conduct an analysis for ${\Xi }_b(6227{)}^0$ state considering it as isospin partner of the ${\Xi }_b(6227{)}^{-}$ resonance and possibly $1P$ or $2S$ excited state with spin $J=\frac{3}{2}$. The corresponding masses for both possibilities have consistent results with the experimental data, indicating that only with the mass sum rules, one can not make exact decision on the nature and quantum numbers of this state. To go further, the decays of these possible excited states to ${\Xi }_b^{-}{\pi }^{+}$ final state are also considered and the relevant strong coupling constants are extracted from the light cone sum rules. The obtained decay width values support the possibility of ${\Xi }_b(6227{)}^0$ to be the $1P$ excited state of ${\Xi }_b(5945{)}^0$ baryon.

   hep-phhep-exhep-latJHEP(2021)·12 citations
7. 07*

   KNO-like scaling within a jet in proton--proton collisions at LHC energies

   Robert Vertesi (1)🇭🇺 · Antal Gemes (2,1)🇬🇧 · Gergely Gabor Barnafoldi (1) ((1) Wigner Research Centre for Physics, (2) Cambridge University)🇭🇺

   We study the multiplicity distributions of events with hard jets in proton-proton collisions at LHC energies using PYTHIA 8 Monte-Carlo simulations. We demonstrate that the charged-hadron multiplicity distributions scale with jet momentum. This suggests that the Koba--Nielsen--Olesen (KNO) scaling holds within a jet. The in-jet scaling is fulfilled without multiple-parton interactions (MPI), but breaks down in case MPI is present without color reconnection. Our findings imply that KNO scaling is violated by parton shower or multiple-parton interactions in higher-energy collisions.

   hep-phPRD(2021)·19 citations
8. 08*

   Excited $K$ meson, $K_c(4180)$, with hidden charm as a $D\bar{D}K$ bound state

   Tian-Wei Wu🇨🇳 · Ming-Zhu Liu🇨🇳 · Li-Sheng Geng🇨🇳

   Motivated by the recent discovery of two new states in the $B^{+}\to D^{+}{D}^{-}{K}^{+}$ decay by the LHCb Collaboration, we study the $D\bar{D}K$ three-body system by solving the Schrödinger equation with the Gaussian Expansion Method. We show that the $D\bar{D}K$ system can bind with quantum numbers $I(J^P)=\frac{1}{2}(0^{-})$ and a binding energy of $B_3(D\bar{D}K)=48.9_{-2.4}^{+1.4}$ MeV. It can decay into $J/\psi K$ and $D_s{\bar{D}}^{\ast }$ via triangle diagrams, yielding a partial decay width of about 1 MeV. As a result, if discovered, it will serve as a highly nontrivial check on the nature of the many exotic hadrons discovered so far and on non-perturbative QCD as well. Assuming heavy quark spin symmetry, the same formalism is applied to study the $D{\bar{D}}^{\ast }K$ system, which is shown to also bind with quantum numbers $I(J^P)=\frac{1}{2}(1^{-})$ and a binding energy of $B_3(D{\bar{D}}^{\ast }K)\simeq 77.3_{-6.6}^{+3.1}$ MeV, consistent with the results of previous works.

   hep-phhep-exhep-latPRD(2021)·40 citations
9. 09*

   Searching for the dark sector in two-body anti-muon decay with the polarization of monochromatic positrons

   Marco Fabbrichesi🇮🇹 · Emidio Gabrielli🇮🇹

   The ${\mu }^{+}\to e^{+}X$ decay, where $X$ is a dark sector boson, provides one of the strongest available bounds on the scale of dark sector interactions. The $X$ boson can be an axion or a dark photon. We show that the concurrent determination of the anti-muon and positron polarizations makes possible to distinguish with a confidence level of 99% between the two dark sector portals with as few as 6 observed events in the case of the massless dark photon. Instead, the massive spin-1, dimension 4 dark portal cannot be distinguished from the axion-like case. We also discuss the possibility that the $X$ boson be a massive spin-2 particle.

   hep-phhep-exPRD(2021)·1 citation
10. 10*

    Bottomonium suppression in an open quantum system using the quantum trajectories method

    Nora Brambilla🇩🇪 · Miguel Ángel Escobedo🇪🇸 · Michael Strickland🇺🇸 · Antonio Vairo🇩🇪 · Peter Vander Griend🇩🇪 · Johannes Heinrich Weber🇩🇪

    We solve the Lindblad equation describing the Brownian motion of a Coulombic heavy quark-antiquark pair in a strongly coupled quark-gluon plasma using the highly efficient Monte Carlo wave-function method. The Lindblad equation has been derived in the framework of pNRQCD and fully accounts for the quantum and non-Abelian nature of the system. The hydrodynamics of the plasma is realistically implemented through a 3+1D dissipative hydrodynamics code. We compute the bottomonium nuclear modification factor and compare with the most recent LHC data. The computation does not rely on any free parameter, as it depends on two transport coefficients that have been evaluated independently in lattice QCD. Our final results, which include late-time feed down of excited states, agree well with the available data from LHC 5.02 TeV PbPb collisions.

    hep-phnucl-exnucl-thphysics.comp-phJHEP(2021)·101 citations
11. 11*

    Graph Neural Networks for Particle Tracking and Reconstruction

    Javier Duarte🇺🇸 · Jean-Roch Vlimant🇺🇸

    Machine learning methods have a long history of applications in high energy physics (HEP). Recently, there is a growing interest in exploiting these methods to reconstruct particle signatures from raw detector data. In order to benefit from modern deep learning algorithms that were initially designed for computer vision or natural language processing tasks, it is common practice to transform HEP data into images or sequences. Conversely, graph neural networks (GNNs), which operate on graph data composed of elements with a set of features and their pairwise connections, provide an alternative way of incorporating weight sharing, local connectivity, and specialized domain knowledge. Particle physics data, such as the hits in a tracking detector, can generally be represented as graphs, making the use of GNNs natural. In this chapter, we recapitulate the mathematical formalism of GNNs and highlight aspects to consider when designing these networks for HEP data, including graph construction, model architectures, learning objectives, and graph pooling. We also review promising applications of GNNs for particle tracking and reconstruction in HEP and summarize the outlook for their deployment in current and future experiments.

    hep-phhep-exphysics.data-anArtificial Intelligence for High Energy P…·58 citations
12. 12*

    Gluon parton densities in soft-wall AdS/QCD

    Valery E. Lyubovitskij🇩🇪 · Ivan Schmidt🇨🇱

    We study the gluon parton densities [parton distribution functions (PDFs), transverse momentum distributions (TMDs), generalized parton distributions (GPDs)] and form factors in soft-wall AdS/QCD. We show that the power behavior of gluon parton distributions and form factors at large values of the light-cone variable and large values of square momentum is consistent with quark counting rules. We also show that the transverse momentum distributions derived in our approach obey the model-independent Mulders-Rodrigues inequalities without referring to specific model parameters. All gluon parton distributions are defined in terms of the unpolarized and polarized gluon PDFs and profile functions. The latter are related to gluon PDFs via differential equations.

    hep-phPRD(2021)·20 citations
13. 13*

    NLO QCD corrections to off-shell $t\bar{t}{W}^{\pm }$ production at the LHC: Correlations and Asymmetries

    Giuseppe Bevilacqua🇭🇺 · Huan-Yu Bi🇩🇪 · Heribertus Bayu Hartanto🇬🇧 · Manfred Kraus🇺🇸 · Jasmina Nasufi🇩🇪 · Malgorzata Worek🇩🇪

    Recent discrepancies between theoretical predictions and experimental data in multi-lepton plus $b$-jets analyses for the $t\bar{t}{W}^{\pm }$ process, as reported by the ATLAS collaboration, have indicated that more accurate theoretical predictions and high precision observables are needed to constrain numerous new physics scenarios in this channel. To this end we employ NLO QCD computations with full off-shell top quark effects included to provide theoretical predictions for the $\mathcal{R}={\sigma }_{t\bar{t}{W}^{+}}/{\sigma }_{t\bar{t}{W}^{-}}$ cross section ratio at the LHC with $\sqrt{s}=13$ TeV. Depending on the transverse momentum cut on the $b$-jet we obtain $2\%-3\%$ theoretical precision on $\mathcal{R}$, which should help to shed some light on new physics effects that can reveal themselves only once sufficiently precise Standard Model theoretical predictions are available. Furthermore, triggered by these discrepancies we reexamine the charge asymmetry of the top quark and its decay products in the $t\bar{t}{W}^{\pm }$ production process. In the case of charge asymmetries, that are uniquely sensitive to the chiral nature of possible new physics in this channel, theoretical uncertainties below $15\%$ are obtained. Additionally, the impact of the top quark decay modelling is scrutinised by explicit comparison with predictions in the narrow-width approximation.

    hep-phEPJC(2021)·49 citations
14. 14*

    SUSY Breaking Constraints on Modular flavor $S_3$ Invariant $SU(5)$ GUT Model

    Xiaokang Du🇨🇳 · Fei Wang🇨🇳

    Modular flavor symmetry can be used to explain the quark and lepton flavor structures. The SUSY partners of quarks and leptons, which share the same superpotential with the quarks and leptons, will also be constrained by the modular flavor structure and show a different flavor(mixing) pattern at the GUT scale. So, in realistic modular flavor models with SUSY completion, constraints from the collider and DM constraints can also be used to constrain the possible values of the modulus parameter. In the first part of this work, we discuss the possibility that the $S_3$ modular symmetry can be preserved by the fixed points of $T^2/Z_N$ orbifold, especially from $T^2/Z_2$. To illustrate the additional constraints from collider etc on modular flavor symmetry models, we take the simplest UV SUSY-completion $S_3$ modular invariance SU(5) GUT model as an example with generalized gravity mediation SUSY breaking mechanism. We find that such constraints can indeed be useful to rule out a large portion of the modulus parameters. Our numerical results show that the UV-completed model can account for both the SM (plus neutrino) flavor structure and the collider, DM constraints. Such discussions can also be applied straightforwardly to other modular flavor symmetry models, such as $A_4$ or $S_4$ models.

    hep-phJHEP(2021)·59 citations
15. 15*

    Directional detection of light dark matter from three-phonon events in superfluid ${}^4$He

    Andrea Caputo🇮🇱 · Angelo Esposito🇨🇭 · Fulvio Piccinini🇮🇹 · Antonio D. Polosa🇮🇹 · Giuseppe Rossi🇮🇹

    We present the analysis of a new signature for light dark matter detection with superfluid ${}^4$He: the emission of three phonons. We show that, in a region of mass below the MeV, the kinematics of this process can offer a way to reconstruct the dark matter interaction vertex, while providing background rejection via coincidence requirements and directionality. We develop all the necessary technology to deal with such an observable, and compute the associated differential distributions.

    hep-phastro-ph.COcond-mat.otherPRD(2021)·29 citations
16. 16*

    On New Physics Contributions to the Higgs Decay to $Z\gamma$

    Paul Archer-Smith🇨🇦 · Daniel Stolarski🇨🇦 · Roberto Vega-Morales🇪🇸

    We explore models of new physics that can give rise to large (100% or more) enhancements to the rate of Higgs decay to $Z\gamma$ while still being consistent with other measurements. We show that this is impossible in simple models with one additional multiplet and also in well motivated models such as the MSSM and folded SUSY. We do find models with several multiplets that carry electroweak charge where such an enhancement is possible, but they require destructive interference effects. We also show that kinematic measurements in Higgs decay to four leptons can be sensitive to such models. Finally we explore the sensitivity of four lepton measurements to supersymmetric models and find that while the measurement is difficult with the high luminosity LHC, it may be possible with a future high energy hadron collider.

    hep-phJHEP(2021)·10 citations
17. 17*

    Neutrino Masses from Low Scale Partial Compositeness

    Zackaria Chacko🇺🇸 · Patrick J. Fox🇺🇸 · Roni Harnik🇺🇸 · Zhen Liu🇺🇸

    We consider a class of models in which the neutrinos acquire Majorana masses through mixing with singlet neutrinos that emerge as composite states of a strongly coupled hidden sector. In this framework, the light neutrinos are partially composite particles that obtain their masses through the inverse seesaw mechanism. We focus on the scenario in which the strong dynamics is approximately conformal in the ultraviolet, and the compositeness scale lies at or below the weak scale. The small parameters in the Lagrangian necessary to realize the observed neutrino masses can naturally arise as a consequence of the scaling dimensions of operators in the conformal field theory. We show that this class of models has interesting implications for a wide variety of experiments, including colliders and beam dumps, searches for lepton flavor violation and neutrinoless double beta decay, and cosmological observations. At colliders and beam dumps, this scenario can give rise to striking signals involving multiple displaced vertices. The exchange of hidden sector states can lead to observable rates for flavor violating processes such as $\mu \to e\gamma$ and $\mu \to e$ conversion. If the compositeness scale lies at or below a hundred MeV, the rate for neutrinoless double beta decay is suppressed by form factors and may be reduced by an order of magnitude or more. The late decays of relic singlet neutrinos can give rise to spectral distortions in the cosmic microwave background that are large enough to be observed in future experiments.

    hep-phJHEP(2021)·28 citations
18. 18*

    Lower Mass Bounds on FIMP Dark Matter Produced via Freeze-In

    Francesco D'Eramo🇮🇹 · Alessandro Lenoci🇩🇪

    Feebly Interacting Massive Particles (FIMPs) are dark matter candidates that never thermalize in the early universe and whose production takes place via decays and/or scatterings of thermal bath particles. If FIMPs interactions with the thermal bath are renormalizable, a scenario which is known as freeze-in, production is most efficient at temperatures around the mass of the bath particles and insensitive to unknown physics at high temperatures. Working in a model-independent fashion, we consider three different production mechanisms: two-body decays, three-body decays, and binary collisions. We compute the FIMP phase space distribution and matter power spectrum, and we investigate the suppression of cosmological structures at small scales. Our results are lower bounds on the FIMP mass. Finally, we study how to relax these constraints in scenarios where FIMPs provide a sub-dominant dark matter component.

    hep-phastro-ph.COJCAP(2021)·127 citations
19. 19*

    Impact of Helical Electromagnetic Fields on the Axion Window

    Takeshi Kobayashi🇯🇵 · Rajeev Kumar Jain🇮🇳

    Primordial electromagnetic fields can strongly affect the cosmic evolution of axions, and vice versa. We show that if helical electromagnetic fields are coherently produced in the early universe, their remnants source a field velocity to the coupled axions and enhance the relic abundance of axion dark matter. We discuss the implications for the QCD axion and axion-like particles that are coupled to the SM or hidden gauge groups. For a QCD axion coupled to hidden photons, we find that the conventional window for the axion decay constant $10^8\mathrm{GeV}\lesssim f\lesssim 10^{12}\mathrm{GeV}$ can be completely closed due to overproduction of axion dark matter by helical electromagnetic fields as little as $\alpha \Delta N_{\mathrm{eff}}\gtrsim 10^{-12}$, where $\alpha$ is the gauge coupling and $\Delta N_{\mathrm{eff}}$ is the effective extra relativistic degrees of freedom of the hidden photons.

    ↳ astro-ph.COhep-phhep-thJCAP(2021)·8 citations
20. 20*

    Past, present, and future of precision determinations of the QCD coupling from lattice QCD

    Mattia Dalla Brida🇮🇹

    Non-perturbative scale-dependent renormalization problems are ubiquitous in lattice QCD as they enter many relevant phenomenological applications. They require solving non-perturbatively the renormalization group equations for the QCD parameters and matrix elements of interest in order to relate their non-perturbative determinations at low energy to their high-energy counterparts needed for phenomenology. Bridging the large energy separation between the hadronic and perturbative regimes of QCD, however, is a notoriously difficult task. In this contribution we focus on the case of the QCD coupling. We critically address the common challenges that state-of-the-art lattice determinations have to face in order to be significantly improved. In addition, we review a novel strategy that has been recently put forward in order to solve this non-perturbative renormalization problem and discuss its implications for future precision determinations. The new ideas exploit the decoupling of heavy quarks to match $N_{\mathrm{f}}$-flavor QCD and the pure Yang-Mills theory. Through this matching the computation of the non-perturbative running of the coupling in QCD can be shifted to the computationally much easier to solve pure-gauge theory. We shall present results for the determination of the $\Lambda$-parameter of $N_{\mathrm{f}}=3$-flavor QCD where this strategy has been applied and proven successful. The results demonstrate that these techniques have the potential to unlock unprecedented precision determinations of the QCD coupling from the lattice. The ideas are moreover quite general and can be considered to solve other non-perturbative renormalization problems.

    ↳ hep-lathep-exhep-phEPJA(2021)·24 citations
21. 21*

    Precession of spheroids under Lorentz violation and observational consequences for neutron stars

    Rui Xu🇨🇳 · Yong Gao🇨🇳 · Lijing Shao🇨🇳

    The Standard-Model Extension (SME) is an effective-field-theoretic framework that catalogs all Lorentz-violating field operators. The anisotropic correction from the minimal gravitational SME to Newtonian gravitational energy for spheroids is studied, and the rotation of rigid spheroids is solved with perturbation method and numerical approach. The well-known forced precession solution given by Nordtvedt in the parameterized post-Newtonian formalism is recovered and applied to two observed solitary millisecond pulsars to set bounds on the coefficients for Lorentz violation in the SME framework. A different solution, which describes the rotation of an otherwise free-precessing star in the presence of Lorentz violation, is found, and its consequences on pulsar signals and continuous gravitational waves (GWs) emitted by neutron stars (NSs) are investigated. The study provides new possible tests of Lorentz violation once free-precessing NSs are firmly identified in the future.

    ↳ gr-qcastro-ph.HEhep-phPRD(2021)·13 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.