Wed·Dec 23, 2020Wednesday·December 23, 2020

1. 01*

   Data-driven dispersive analysis of the $\pi \pi$ and $\pi K$ scattering

   Igor Danilkin🇩🇪 · Oleksandra Deineka🇩🇪 · Marc Vanderhaeghen🇩🇪

   We present a data-driven analysis of the resonant S-wave $\pi \pi \to \pi \pi$ and $\pi K\to \pi K$ reactions using the partial-wave dispersion relation. The contributions from the left-hand cuts are accounted for using the Taylor expansion in a suitably constructed conformal variable. The fits are performed to experimental and lattice data as well as Roy analyses. For the $\pi \pi$ scattering we present both a single- and coupled-channel analysis by including additionally the $K\bar{K}$ channel. For the latter the central result is the Omnès matrix, which is consistent with the most recent Roy and Roy-Steiner results on $\pi \pi \to \pi \pi$ and $\pi \pi \to K\bar{K}$, respectively. By the analytic continuation to the complex plane, we found poles associated with the lightest scalar resonances $\sigma /f_0(500)$, $f_0(980)$, and $\kappa /K_0^{\ast }(700)$ for the physical pion mass value and in the case of $\sigma /f_0(500)$, $\kappa /K_0^{\ast }(700)$ also for unphysical pion mass values.

   hep-phPRD(2021)·40 citations
2. 02*

   TASI 2020 Lectures on Precision Tests of the Standard Model

   Ayres Freitas🇺🇸

   This write-up of lectures given at TASI 2020 provides an introduction into precision tests of the electroweak Standard Model. The lecture notes begin with a hands-on review of the (on-shell) renormalization procedure, and subsequently highlight a few subtleties that occur in the renormalization of a theory with electroweak symmetry breaking and massive gauge bosons. After that a set of typical electroweak precision observables is introduced, as well as a range of input parameter measurements that are needed for making predictions within the Standard Model. Finally, it is discussed how comparisons of the electroweak precision observables between experiment and theory can be used to stress-test the Standard Model and probe new physics.

   hep-phPoS(2021)·19 citations
3. 03*

   Electromagnetic form factors of the ${\Omega }^{-}$ baryon in the spacelike and timelike regions

   G. Ramalho🇧🇷

   We present complete calculations of the electromagnetic form factors of the ${\Omega }^{-}$ in the spacelike region and in the timelike region. The four elastic form factors: electric charge ($G_{E0}$), magnetic dipole ($G_{M1}$), electric quadrupole ($G_{E2}$) and magnetic octupole ($G_{M3}$), are estimated within the covariant spectator quark model, in terms of the square momentum transfer $q^2$. The free parameters of the ${\Omega }^{-}$ wave function, including a $S$-wave state and two independent $D$-wave states radial wave functions and the admixture coefficients are fixed by the comparison with the lattice QCD data in the spacelike region ($Q^2=-q^2\le 0$) and with the recent $e^{+}{e}^{-}\to {\Omega }^{-}{\bar{\Omega }}^{+}$ data from CLEO in the timelike region ($q^2>0$). The estimates in the timelike region for square momentum transfer $q^2\ge 4M_{\Omega }^2$ are based on large-$q^2$ asymptotic relations ($M_{\Omega }$ is the ${\Omega }^{-}$ mass). We examine also the impact of the large-$Q^2$ correlations between different form factors and analyze the possible solutions. The electric quadrupole and the magnetic octupole moments of the ${\Omega }^{-}$, and the $e^{+}{e}^{-}\to {\Omega }^{-}{\bar{\Omega }}^{+}$ integrated cross sections for very large $q^2$ are estimated based on the model results.

   hep-phhep-exhep-latnucl-ex+1PRD(2021)·22 citations
4. 04*

   Kinematic Azimuthal Asymmetries and Lam-Tung Relation

   O.V. Teryaev🇷🇺

   The origin of Lam-Tung relation for the angular asymmetry of Drell-Yan dileptons is analyzed. The asymmetry constrained by this relation is shown to belongto the class of kinematic azimuthal asymmetries, emerging due to the deviation of the reference axis from the natural physical one. The validity and violation of Lam-Tung relation due to radiative and power QCD corrections is discussed. The relation is generalized to the case when the virtual photon is not the transverse oneand the possible applications are suggested.

   hep-phnucl-th4 citations
5. 05*

   Pseudoscalar corrections to spin motion equation, search for electric dipole moment and muon magnetic (g-2) factor

   V. G. Baryshevsky🇧🇾 · P. I. Porshnev🇧🇾

   The spin dynamics in constant electromagnetic fields is described by the Bargmann-Michel-Telegdi equation which can be upgraded with anomalous magnetic and electric dipole moments. The upgraded equation remains self-consistent, Lorentz-covariant and gauge-invariant. It and its different forms have been confirmed in numerous experiments to high degree of accuracy. We have recently derived the spin motion equation within the Wentzel-Kramers-Brillouin weak-field approximation which adds a pseudoscalar correction to the BMT equation. The upgraded equation is again self-consistent, Lorentz-covariant, gauge-invariant, and free of unwanted artifacts. The pseudoscalar correction is expected to be small, and might become important in hypersensitive experiments, like the measurements of electric dipole moments which are themselves related to pseudoscalar quantities. It also becomes possible to explain why EDMs are so difficult to measure, since this correction term might lead to the effective screening of electric dipole moments. Within the same model, it is possible to explain the discrepancy between experimental and theoretical values of muon magnetic anomaly under assumption that the pseudoscalar correction is the dominant source of this discrepancy.

   hep-phhep-th4 citations
6. 06*

   Forbidden Dark Matter Annihilations into Standard Model Particles

   Raffaele Tito D'Agnolo🇫🇷 · Di Liu🇩🇪 · Joshua T. Ruderman🇺🇸 · Po-Jen Wang🇺🇸

   We present kinematically forbidden dark matter annihilations into Standard Model leptons. This mechanism precisely selects the dark matter mass that gives the observed relic abundance. This is qualitatively different from existing models of thermal dark matter, where fixing the relic density typically leaves open orders of magnitude of viable dark matter masses. Forbidden annihilations require the dark matter to be close in mass to the particles that dominate its annihilation rate. We show examples where the dark matter mass is close to the muon mass, the tau mass, or the average of the tau and muon masses. We find that most of the relevant parameter space can be covered by the next generation of proposed beam-dump experiments and future high-luminosity electron positron colliders. Forbidden dark matter predicts large couplings to the Standard Model that can explain the observed value of $(g-2{)}_{\mu }$.

   hep-phJHEP(2021)·47 citations
7. 07*

   $B$ anomalies with unparticles

   Jong-Phil Lee🇰🇷

   We analyze the $B$ anomalies associated with the $B\to D^{(\ast )}\tau \nu$ decays in the unparticle model. The fraction of the branching ratios $R(D^{(\ast )})$ and other parameters related to the polarization are fitted to the experimental data by minimizing ${\chi }^2$. The best-fit values are $R(D{)}_{\mathrm{best}}=0.371$ and $R(D^{\ast }{)}_{\mathrm{best}}=0.266$ which are still larger than the standard model predictions. We find that our results safely render the branching ratio $\mathrm{Br}(B_c\to \tau \nu )$ below $10\%$.

   hep-phMod.Phys.Lett.A(2021)·3 citations
8. 08*

   Analysis of the hidden-charm tetraquark molecule mass spectrum with the QCD sum rules

   Zhi-Gang Wang🇨🇳

   In this article, we investigate the mass spectrum of the ground state hidden-charm tetraquark molecular states without strange, with strange and with hidden-strange via the QCD sum rules in a comprehensive way and revisit the assignments of the $X$, $Y$, $Z$ states in the scenario of tetraquark molecular states consistently based on the QCD sum rules.

   hep-phInt.J.Mod.Phys.A(2021)·72 citations
9. 09*

   A unified description of the hidden-charm tetraquark states $Z_{cs}(3985)$, $Z_c(3900)$ and $X(4020)$

   Zhi-Hui Guo🇨🇳 · J. A. Oller🇪🇸

   The newly observed hidden-charm tetraquark state $Z_{cs}(3985)$, together with $Z_c(3900)$ and $X(4020)$, are studied in the combined theoretical framework of the effective range expansion, compositeness relation and the decay width saturation. The elastic effective-range-expansion approach leads to sensible results for the scattering lengths, effective ranges and the compositeness coefficients, $i.e.$, the probabilities to find the two-charm-meson molecule components in the tetraquark states. The coupled-channel formalism by including the $J/\psi \pi$ and $D{\bar{D}}^{\ast }/\bar{D}{D}^{\ast }$ to fulfill the constraints of the compositeness relation and the decay width, confirms the elastic effective-range-expansion results for the $Z_c(3900)$, by using the experimental inputs for the ratios of the decay widths between $D{\bar{D}}^{\ast }/\bar{D}{D}^{\ast }$ and $J/\psi \pi$. With the results from the elastic effective-range-expansion study as input for the compositeness, we generalize the discussions to the $Z_{cs}(3985)$ by including the $J/\psi K^{-}$ and $D_s^{-}{D}^{\ast 0}/D_s^{\ast -}{D}^0$, and predict the partial decay widths of the $J/\psi K^{-}$. Similar calculations are also carried out for the $X(4020)$ by including the $h_c\pi$ and $D^{\ast }{\bar{D}}^{\ast }$, and the partial decay widths of the $h_c\pi$ is predicted. Our results can provide useful guidelines for future experimental measurements.

   hep-phhep-exPRD(2021)·34 citations
10. 10*

    BFKL -- past and future

    Victor Fadin🇷🇺

    This paper contains my recollection of the creation and development of the so-called BFKL approach and my ideas about the ways of its further development.

    hep-ph9 citations
11. 11*

    How to GAN Higher Jet Resolution

    Pierre Baldi🇺🇸 · Lukas Blecher🇩🇪 · Anja Butter🇩🇪 · Julian Collado🇺🇸 · Jessica N. Howard🇺🇸 · Fabian Keilbach🇩🇪 · Tilman Plehn🇩🇪 · Gregor Kasieczka🇩🇪 · Daniel Whiteson🇺🇸

    QCD-jets at the LHC are described by simple physics principles. We show how super-resolution generative networks can learn the underlying structures and use them to improve the resolution of jet images. We test this approach on massless QCD-jets and on fat top-jets and find that the network reproduces their main features even without training on pure samples. In addition, we show how a slim network architecture can be constructed once we have control of the full network performance.

    hep-phSciPost Phys.(2022)·32 citations
12. 12*

    Centrality dependence of dilepton production via $\gamma \gamma$ processes from Wigner distributions of photons in nuclei

    Mariola Kłusek-Gawenda🇵🇱 · Wolfgang Schäfer🇵🇱 · Antoni Szczurek🇵🇱

    We propose a new complete method, based on the Wigner distributions of photons, how to calculate differential distributions of dileptons created via photon-photon fusion in semicentral ($b<2R_A$) $AA$ collisions. The formalism is used to calculate different distributions of invariant mass, dilepton transverse momentum and acoplanarity for different regions of centrality. The results of calculation are compared with recent STAR, ALICE and ATLAS experimental data. Very good agreement with the data is achieved without free parameters and without including additional mechanisms such as a possible rescattering of leptons in the quark-gluon plasma.

    hep-phhep-thPLB(2021)·40 citations
13. 13*

    Charm Hadrons in pp collisions at LHC energy within a Coalescence plus Fragmentation approach

    Vincenzo Minissale (1 and 2)🇮🇹 · Salvatore Plumari (1 and 2)🇮🇹 · Vincenzo Greco (1 and 2) ((1) Department of Physics and Astronomy 'E. Majorana', University of Catania, (2) Laboratori Nazionali del Sud, INFN-LNS)🇮🇹

    The recent experimental measurements on $pp$ collisions at $\sqrt{s}=5.02\mathrm{TeV}$ have shown a very large abundance of heavy baryon production corresponding to a ratio of ${\Lambda }_c/D^0\sim 0.6$, about one order of magnitude larger than what measured in $e^{+}{e}^{-}$, $ep$ collisions and even in $pp$ collisions at LHC, but at forward rapidity. We apply for the first time to $pp$ collisions a quark coalescence plus fragmentation approach developed for $AA$ collisions, assuming the formation of Hot QCD matter at finite temperature. An approach that has correctly predicted a ${\Lambda }_c/D\sim O(1)$ in AA collisions at RHIC energy. We calculate the heavy baryon/meson ratio and the $p_T$ spectra of charmed hadrons with and without strangeness content: $D^0$, $D_s$, ${\Lambda }_c^{+}$, ${\Xi }_c$ and ${\Omega }_c$ in $pp$ collisions at top LHC energies, finding a satisfactory result for the measured ${\Lambda }_c^{+}/D^0$ and the ${\Xi }_c/D^0$ without any specific tuning of parameters to $pp$ collisions. At variance with other approaches a coalescence approach predicts also a significant production of ${\Omega }_c$ such that ${\Omega }_c/D^0\sim O(10^{-1})$ .

    hep-phPLB(2021)·144 citations
14. 14*

    Gravitational Vector Dark Matter

    Christian Gross🇮🇹 · Sotirios Karamitsos🇮🇹 · Giacomo Landini🇮🇹 · Alessandro Strumia🇮🇹

    A new dark sector consisting of a pure non-abelian gauge theory has no renormalizable interaction with SM particles, and can thereby realise gravitational Dark Matter (DM). Gauge interactions confine at a scale ${\Lambda }_{\mathrm{DM}}$ giving bound states with typical lifetimes $\tau \sim M_{\mathrm{Pl}}^4/{\Lambda }_{\mathrm{DM}}^5$ that can be DM candidates if ${\Lambda }_{\mathrm{DM}}$ is below 100 TeV. Furthermore, accidental symmetries of group-theoretical nature produce special gravitationally stable bound states. In the presence of generic Planck-suppressed operators such states become long-lived: SU$(N)$ gauge theories contain bound states with $\tau \sim M_{\mathrm{Pl}}^8/{\Lambda }_{\mathrm{DM}}^9$; even longer lifetimes $\tau =(M_{\mathrm{Pl}}/{\Lambda }_{\mathrm{DM}}{)}^{2N-4}/{\Lambda }_{\mathrm{DM}}$ arise from SO$(N)$ theories with $N\ge 8$, and possibly from $F_4$ or $E_8$. We compute their relic abundance generated by gravitational freeze-in and by inflationary fluctuations, finding that they can be viable DM candidates for ${\Lambda }_{\mathrm{DM}}\gtrsim 10^{10}$ GeV.

    hep-phJHEP(2021)·42 citations
15. 15*

    QCD sum rules for parameters of the $B$-meson distribution amplitudes

    Muslem Rahimi🇩🇪 · Marcel Wald🇩🇪

    We obtain new estimates for the parameters ${\lambda }_E^2$, ${\lambda }_H^2$ and their ratio $\mathcal{R}={\lambda }_E^2/{\lambda }_H^2$, which appear in the second moments of the $B$-meson light-cone distribution amplitudes defined in the heavy-quark effective field theory. The computation is based on two-point QCD sum rules for the diagonal correlation function and includes all contributions up to mass dimension seven in the operator-product expansion. For the ratio we get $\mathcal{R}=(0.1\pm 0.1)$ with ${\lambda }_H^2=(0.15\pm 0.05){\text{GeV}}^2$ and ${\lambda }_E^2=(0.01\pm 0.01){\text{GeV}}^2$.

    hep-phPRD(2021)·29 citations
16. 16*

    Model independent analysis of the angular observables in $B^0\to K^{\ast 0}{\mu }^{+}{\mu }^{-}$ and $B^{+}\to K^{\ast +}{\mu }^{+}{\mu }^{-}$

    T. Hurth🇩🇪 · F. Mahmoudi🇫🇷 · S. Neshatpour🇫🇷

    We analyse the results recently presented on the $B^{+}\to K^{\ast +}{\mu }^{+}{\mu }^{-}$ angular observables by the LHCb Collaboration which show indications for New Physics beyond the Standard Model. Within a model-independent analysis, we compare the fit results with the corresponding results for the angular observables in $B^0\to K^{\ast 0}{\mu }^{+}{\mu }^{-}$.

    hep-phPRD(2021)·48 citations
17. 17*

    smelli -- the SMEFT Likelihood

    Peter Stangl🇨🇭

    I present the Python package smelli that implements a global likelihood function in the space of dimension-six Wilson coefficients in the Standard Model Effective Field Theory (SMEFT). The likelihood includes contributions from a large number of flavor and other precision observables, currently 399 in total.

    hep-phPoS(2021)·26 citations
18. 18*

    Top quark loop corrections to $W^{+}{W}^{-}$ scattering in EChL

    Antonio Dobado🇪🇸 · Carlos Quezada-Calonge🇪🇸 · Juan José Sanz-Cillero🇪🇸

    We calculate fermion-loop corrections to high energy $W^{+}{W}^{-}$ scattering in the context of a Strongly Interacting Electroweak Symmetry Breaking Sector (EWSBS) using Higgs Effective Field Theory(HEFT). We test the assumption that these corrections are negligible when compared to the boson-loop ones, as it is commonly taken for granted in the literature. While this is correct inmost cases, we find that, for some particular regions of the parameter space, fermion-loops can be important: deviations in the couplings of the HEFT from their Standard Model values may lead to fermion-loop corrections as relevant as the boson-loop ones.

    hep-phPoS(2021)·3 citations
19. 19*

    Small ${\theta }_{13}$ and solar neutrino oscillation parameters from $\mu -\tau$ symmetry

    Abdel Pérez-Lorenzana🇲🇽

    Exchange $\mu -\tau$ symmetry in the effective Majorana neutrino mass matrix does predict a maximal mixing for atmospheric neutrino oscillations asides to a null mixing that cannot be straightforwardly identified with reactor neutrino oscillation mixing, ${\theta }_{13}$, unless a specific ordering is assumed for the mass eigenstates. Otherwise, a non zero value for ${\theta }_{13}$ is predicted already at the level of an exact symmetry. In this case, solar neutrino mixing and scale, as well as the correct atmospheric mixing, arise from the breaking of the symmetry. I present a mass matrix proposal for normal hierarchy that realizes this scenario, where the smallness of $\tan {\theta }_{13}$ is naturally given by the parameter $ϵ\sim \sqrt{\Delta m_{sol}^2/\Delta m_{ATM}^2}$ and the solar mixing is linked to the smallness of $\Delta m_{sol}^2$. The proposed matrix remains stable under renormalization effects and it also allows to account for CP violation within the expected region without further constrains.

    hep-phhep-thInt.J.Mod.Phys.A(2021)·2 citations
20. 20*

    Artificial Proto-Modelling: Building Precursors of a Next Standard Model from Simplified Model Results

    Wolfgang Waltenberger🇦🇹 · André Lessa🇧🇷 · Sabine Kraml🇫🇷

    We present a novel algorithm to identify potential dispersed signals of new physics in the slew of published LHC results. It employs a random walk algorithm to introduce sets of new particles, dubbed "proto-models", which are tested against simplified-model results from ATLAS and CMS (exploiting the SModelS software framework). A combinatorial algorithm identifies the set of analyses and/or signal regions that maximally violates the SM hypothesis, while remaining compatible with the entirety of LHC constraints in our database. Demonstrating our method by running over the experimental results in the SModelS database, we find as currently best-performing proto-model a top partner, a light-flavor quark partner, and a lightest neutral new particle with masses of the order of 1.2 TeV, 700 GeV and 160 GeV, respectively. The corresponding global p-value for the SM hypothesis is approximately 0.19; by construction no look-elsewhere effect applies.

    hep-phhep-exstat.APJHEP(2021)·13 citations
21. 21*

    Formation of light (anti)nuclei

    J. Tjemsland🇳🇴

    The production mechanism of light nuclei, such as deuteron, helium-3, tritium and their antiparticles, has recently attracted an increased attention from the astroparticle and heavy ion communities. The expected low astrophysical background of light antinulei makes them ideal probes for exotic astrophysical processes, such as dark matter annihilations. At the same time, they can be used to measure two-nucleon correlations and density fluctuations in heavy ion collisions, which may shed light on the QCD phase diagram. Motivated by the importance of light antinuclei in cosmic ray studies, we developed a new coalescence model for light (anti)nuclei that includes both the size of the formation region, which is process dependent, and momentum correlations in a semi-classical picture. We have employed the model as an afterburner to the event generators Pythia 8 and QGSJET II, and find that the model agrees well with experimental data on antideuteron and antihelium-3 production in $e^{+}{e}^{-}$, $pp$, $p$Be and $p$Al collisions at various energies. In this paper, we review this model and update existing fits to experimental data based on new insights.

    hep-phnucl-thPoS(2021)·5 citations
22. 22*

    The Low-Energy Effective Theory of Axions and ALPs

    Martin Bauer🇬🇧 · Matthias Neubert🇩🇪 · Sophie Renner🇮🇹 · Marvin Schnubel🇩🇪 · Andrea Thamm🇦🇺

    Axions and axion-like particles (ALPs) are well-motivated low-energy relics of high-energy extensions of the Standard Model, which interact with the known particles through higher-dimensional operators suppressed by the mass scale $\Lambda$ of the new-physics sector. Starting from the most general dimension-5 interactions, we discuss in detail the evolution of the ALP couplings from the new-physics scale to energies at and below the scale of electroweak symmetry breaking. We derive the relevant anomalous dimensions at two-loop order in gauge couplings and one-loop order in Yukawa interactions, carefully considering the treatment of a redundant operator involving an ALP coupling to the Higgs current. We account for one-loop (and partially two-loop) matching contributions at the weak scale, including in particular flavor-changing effects. The relations between different equivalent forms of the effective Lagrangian are discussed in detail. We also construct the effective chiral Lagrangian for an ALP interacting with photons and light pseudoscalar mesons, pointing out important differences with the corresponding Lagrangian for the QCD axion.

    hep-phhep-thJHEP(2021)·301 citations
23. 23*

    The role of strangeness in chiral and $U(1{)}_A$ restoration

    Angel Gómez Nicola🇪🇸 · Jacobo Ruiz de Elvira🇨🇭 · Andrea Vioque-Rodríguez🇪🇸 · David Álvarez-Herrero🇪🇸

    We use recently derived Ward identities and lattice data for the light- and strange-quark condensates to reconstruct the scalar and pseudoscalar susceptibilities (${\chi }_S^{\kappa }$, ${\chi }_P^K$) in the isospin 1/2 channel. We show that ${\chi }_S^{\kappa }$ develops a maximum above the QCD chiral transition, after which it degenerates with ${\chi }_P^K$. We also obtain ${\chi }_S^{\kappa }$ within Unitarized Chiral Perturbation Theory (UChPT) at finite temperature, when it is saturated with the $K_0^{\ast }(700)$ (or $\kappa$) meson, the dominant lowest-energy state in the isospin 1/2 scalar channel of $\pi K$ scattering. Such UChPT result reproduces the expected peak structure, revealing the importance of thermal interactions, and makes it possible to examine the ${\chi }_S^{\kappa }$ dependence on the light- and strange-quark masses. A consistent picture emerges controlled by the $m_l/m_s$ ratio that allows one studying $K-\kappa$ degeneration in the chiral, two-flavor and $SU(3)$ limits. These results provide an alternative sign for $O(4)\times U(1{)}_A$ restoration that can be explored in lattice simulations and highlight the role of strangeness, which regulated by the strange-quark condensate helps to reconcile the current tension among lattice results regarding $U(1{)}_A$ restoration.

    hep-phEPJC(2021)·16 citations
24. 24*

    Omega vs. pi, and 6d anomaly cancellation

    Joe Davighi🇬🇧 · Nakarin Lohitsiri🇬🇧

    In this note we review the role of homotopy groups in determining non-perturbative (henceforth `global') gauge anomalies, in light of recent progress understanding global anomalies using bordism. We explain why non-vanishing of ${\pi }_d(G)$ is neither a necessary nor a sufficient condition for there being a possible global anomaly in a $d$-dimensional chiral gauge theory with gauge group $G$. To showcase the failure of sufficiency, we revisit `global anomalies' that have been previously studied in 6d gauge theories with $G=SU(2)$, $SU(3)$, or $G_2$. Even though ${\pi }_6(G)\ne 0$, the bordism groups ${\Omega }_7^{\mathrm{Spin}}(BG)$ vanish in all three cases, implying there are no global anomalies. In the case of $G=SU(2)$ we carefully scrutinize the role of homotopy, and explain why any 7-dimensional mapping torus must be trivial from the bordism perspective. In all these 6d examples, the conditions previously thought to be necessary for global anomaly cancellation are in fact necessary conditions for the local anomalies to vanish.

    ↳ hep-thhep-phJHEP(2021)·33 citations
25. 25*

    The QED four -- photon amplitudes off-shell: part 1

    Naser Ahmadiniaz🇩🇪 · Cristhiam Lopez-Arcos🇲🇽 · Misha A. Lopez-Lopez🇺🇸 · Christian Schubert🇲🇽

    The QED four-photon amplitude has been well-studied by many authors, and on-shell is treated in many textbooks. However, a calculation with all four photons off-shell is presently still lacking, despite of the fact that this amplitude appears off-shell as a subprocess in many different contexts, in vacuum as well as with some photons connecting to external fields. The present paper is the first in a series of four where we use the worldline formalism to obtain this amplitude explicitly in terms of hypergeometric functions, and derivatives thereof, for both scalar and spinor QED. The formalism allows us to unify the scalar and spinor loop calculations, to avoid the usual breaking up of the amplitude into three inequivalent Feynman diagrams, and to achieve manifest transversality as well as UV finiteness at the integrand level by an optimized version of the integration-by-parts procedure originally introduced by Bern and Kosower for gluon amplitudes. The full permutation symmetry is maintained throughout, and the amplitudes get projected naturally into the basis of five tensors introduced by Costantini et al. in 1971. Since in many applications of the "four-photon box" some of the photons can be taken in the low-energy limit, and the formalism makes it easy to integrate out any such leg, apart from the case of general kinematics (part 4) we also treat the special cases of one (part 3) or two (part 2) photons taken at low energy. In this first part of the series, we summarize the application of the worldline formalism to the N-photon amplitudes and its relation to Feynman diagrams, derive the optimized tensor-decomposed integrands of the four-photon amplitudes in scalar and spinor QED, and outline the computational strategy to be followed in parts 2 to 4.

    ↳ hep-thhep-phNPB(2023)·24 citations
26. 26*

    Self-interacting neutrinos, the Hubble parameter tension, and the Cosmic Microwave Background

    Thejs Brinckmann🇺🇸 · Jae Hyeok Chang🇺🇸 · Marilena LoVerde🇺🇸

    We perform a comprehensive study of cosmological constraints on non-standard neutrino self-interactions using cosmic microwave background (CMB) and baryon acoustic oscillation data. We consider different scenarios for neutrino self-interactions distinguished by the fraction of neutrino states allowed to participate in self-interactions and how the relativistic energy density, N${}_{\text{eff}}$, is allowed to vary. Specifically, we study cases in which: all neutrino states self-interact and N${}_{\text{eff}}$ varies; two species free-stream, which we show alleviates tension with laboratory constraints, while the energy in the additional interacting states varies; and a variable fraction of neutrinos self-interact with either the total N${}_{\text{eff}}$ fixed to the Standard Model value or allowed to vary. In no case do we find compelling evidence for new neutrino interactions or non-standard values of N${}_{\text{eff}}$. In several cases we find additional modes with neutrino decoupling occurring at lower redshifts $z_{\text{dec}}\sim 10^{3-4}$. We do a careful analysis to examine whether new neutrino self-interactions solve or alleviate the so-called $H_0$ tension and find that, when all Planck 2018 CMB temperature and polarization data is included, none of these examples ease the tension more than allowing a variable N${}_{\text{eff}}$ comprised of free-streaming particles. Although we focus on neutrino interactions, these constraints are applicable to any light relic particle.

    ↳ astro-ph.COhep-phPRD(2021)·137 citations
27. 27*

    Compact Dark Objects in Neutron Star Mergers

    Andreas Bauswein🇩🇪 · Gang Guo🇹🇼 · Jr-Hua Lien🇹🇼 · Yen-Hsun Lin🇹🇼 · Meng-Ru Wu🇹🇼

    We estimate the long-lasting gravitational wave (GW) emission of compact dark objects following a binary neutron-star (NS) merger. We consider compact dark objects, which initially reside in the centers of NSs and which may consist of self-interacting dark matter (DM). By approximating the compact dark objects as test particles, we model the merging of NS binaries hosting DM components with three-dimensional relativistic simulations. Our simulation results suggest that the DM components remain gravitationally bound and orbit inside the merger remnant with orbital separations of typically a few km. The subsequent orbital motion of the DM components generates a GW signal with frequencies in the range of a few kHz. When considering a range of different binary masses and high-density equations of state (EoS), we find that the GW frequency of the orbiting DM components scales with the compactness of NSs. Similarly, we find relations between the DM GW frequency and the dominant postmerger GW frequency of the stellar fluid or the tidal deformability, which quantifies EoS effects during the binary inspiral. Hence, a measurement of these quantities can be used to specify the frequency range of the GW emission by DM. Under the assumption that GW back reaction is the only relevant dissipative process, the GW signal may last between seconds and years depending on the mass of the DM component. We estimate the detectability of the GW signals and find that DM components in NS mergers may only be detectable with existing and projected GW instruments if the dark objects are as massive as about 0.01 to 0.1 M_sun. We emphasize that the GW emission is limited by the lifetime of the remnant. A forming black hole will immediately swallow the DM objects because their orbits are smaller than the innermost stable circular orbit of the black hole.

    ↳ astro-ph.HEhep-phPRD(2023)·62 citations
28. 28*

    Implications of NANOGrav results and UV freeze-in in a fast-expanding Universe

    Basabendu Barman🇮🇳 · Amit Dutta Banik🇨🇳 · Avik Paul🇮🇳

    Recent pulsar timing data reported by the NANOGrav collaboration indicates the existence of a stochastic gravitational wave (GW) background at a frequency $f\sim 10^{-8}\mathrm{Hz}$. We show that a dark sector consisting of a Standard Model (SM) gauge singlet fermion $\chi$ and a singlet scalar $\varphi$, both charged under a $Z_4$ symmetry, is capable of generating such a low frequency GW via strong first order phase transition (SFOPT) through the modification of the standard cosmological history, where we assume faster-than-usual expansion at pre-BBN times driven by a new cosmological species $\phi$ whose energy density red-shifts with the scale factor as ${\rho }_{\phi }\propto a^{-\left(4+n\right)}$. Depending on the choice of the fast expansion parameters, reheat temperature and effective scale of the theory, it is also possible to address correct dark matter (DM) relic abundance via freeze-in. We show that a successful first order phase transition explaining NANOGrav results together with PLANCK observed DM abundance put bound on the fast expansion parameters requiring $n\lesssim 4$ to explain both.

    ↳ astro-ph.COhep-ph13 citations
29. 29*

    Machine Learning and cosmographic reconstructions of quintessence and the Swampland conjectures

    Rubén Arjona🇪🇸 · Savvas Nesseris🇪🇸

    We present model independent reconstructions of quintessence and the Swampland conjectures (SC) using both Machine Learning (ML) and cosmography. In particular, we demonstrate how the synergies between theoretical analyses and ML can provide key insights on the nature of dark energy and modified gravity. Using the Hubble parameter $H(z)$ data from the cosmic chronometers we find that the ML and cosmography reconstructions of the SC are compatible with observations at low redshifts. Finally, including the growth rate data $f{\sigma }_8(z)$ we perform a model independent test of modified gravity cosmologies through two phase diagrams, namely $H-f{\sigma }_8$ and $\eta -f{\sigma }_8$, where the anisotropic stress parameter $\eta$ is obtained via the $E_g$ statistics, which is related to gravitational lensing data. While the first diagram is consistent within the errors with the $\Lambda$CDM model, the second one has a $\sim 2\sigma$ deviation of the anisotropic stress from unity at $z\sim 0.3$ and a $\sim 4\sigma$ deviation at $z\sim 0.9$, thus pointing toward mild deviations from General Relativity, which could be further tested with upcoming large-scale structure surveys.

    ↳ astro-ph.COgr-qchep-phPRD(2021)·27 citations
30. 30*

    Beam particle tracking with a low-mass mini time projection chamber in the PEN experiment

    C.J. Glaser🇺🇸 · D. Pocanic🇺🇸 · A. van der Schaaf🇨🇭 · V.A. Baranov🇷🇺 · N.V. Khomutov🇷🇺 · N.P. Kravchuk🇷🇺 · N.A. Kuchinsky🇷🇺

    The international PEN collaboration aims to obtain the branching ratio for the pion electronic decay ${\pi }^{+}\to e^{+}{\nu }_e(\gamma )$, aka ${\pi }_{e2}$, to a relative precision of $5\times 10^{-4}$ or better. The PEN apparatus comprises a number of detection systems, all contributing vital information to the PEN event reconstruction. This paper discusses the design, performance, and Monte Carlo simulation of the mini time projection chamber (mTPC) used for pion, muon, and positron beam particle tracking. We also review the use of the extracted trajectory coordinates in the analysis, in particular in constructing observables critical for discriminating background processes, and in maximizing the fiducial volume of the target in which decay event vertices can be accepted for branching ratio extraction without introducing bias.

    ↳ physics.ins-dethep-exhep-phnucl-exNucl.Instrum.Meth.A(2021)·2 citations
31. 31*

    Inferring the Morphology of Stellar Distribution in TNG50: Twisted and Twisted-Stretched shapes

    Razieh Emami (Center for Astrophysics, Harvard & Smithsonian)🇺🇸 · Lars Hernquist🇺🇸 · Charles Alcock🇺🇸 · Shy Genel🇺🇸 · Sownak Bose🇺🇸 · Rainer Weinberger🇺🇸 · Mark Vogelsberger🇺🇸 · Xuejian Shen🇺🇸 · Joshua S. Speagle🇨🇦 · Federico Marinacci🇮🇹 · John C. Forbes🇺🇸 · Paul Torrey🇺🇸

    We investigate the morphology of the stellar distribution in a sample of Milky Way (MW) like galaxies in the TNG50 simulation. Using a local in shell iterative method (LSIM) as the main approach, we explicitly show evidence of twisting (in about 52% of halos) and stretching (in 48% of them) in the real space. This is matched with the re-orientation observed in the eigenvectors of the inertia tensor and gives us a clear picture of having a re-oriented stellar distribution. We make a comparison between the shape profile of dark matter (DM) halo and stellar distribution and quite remarkably see that their radial profiles are fairly close, especially at small galactocentric radii where the stellar disk is located. This implies that the DM halo is somewhat aligned with stars in response to the baryonic potential. The level of alignment mostly decreases away from the center. We study the impact of substructures in the orbital circularity parameter. It is demonstrated that in some cases, far away substructures are counter-rotating compared with the central stars and may flip the sign of total angular momentum and thus the orbital circularity parameter. Truncating them above 150 kpc, however, retains the disky structure of the galaxy as per initial selection. Including the impact of substructures in the shape of stars, we explicitly show that their contribution is subdominant. Overlaying our theoretical results to the observational constraints from previous literature, we establish fair agreement.

    ↳ astro-ph.GAastro-ph.COastro-ph.SRhep-ph+1ApJ(2021)·7 citations
32. 32*

    Cluster algebras for Feynman integrals

    Dmitry Chicherin🇩🇪 · Johannes M. Henn🇩🇪 · Georgios Papathanasiou🇩🇪

    We initiate the study of cluster algebras in Feynman integrals in dimensional regularization. We provide evidence that four-point Feynman integrals with one off-shell leg are described by a $C_2$ cluster algebra, and we find cluster adjacency relations that restrict the allowed function space. By embedding $C_2$ inside the $A_3$ cluster algebra, we identify these adjacencies with the extended Steinmann relations for six-particle massless scattering. The cluster algebra connection we find restricts the functions space for vector boson or Higgs plus jet amplitudes, and for form factors recently considered in $\mathcal{N}=4$ super Yang-Mills. We explain general procedures for studying relationships between alphabets of generalized polylogarithmic functions and cluster algebras, and use them to provide various identifications of one-loop alphabets with cluster algebras. In particular, we show how one can obtain one-loop alphabets for five-particle scattering from a recently discussed dual conformal eight-particle alphabet related to the $G(4,8)$ cluster algebra.

    ↳ hep-thhep-phPRL(2021)·98 citations
33. 33*

    A Three-Point Form Factor Through Five Loops

    Lance J. Dixon🇺🇸 · Andrew J. McLeod🇩🇰 · Matthias Wilhelm🇩🇰

    We bootstrap the three-point form factor of the chiral part of the stress-tensor supermultiplet in planar $\mathcal{N}=4$ super-Yang-Mills theory, obtaining new results at three, four, and five loops. Our construction employs known conditions on the first, second, and final entries of the symbol, combined with new multiple-final-entry conditions, ``extended-Steinmann-like'' conditions, and near-collinear data from the recently-developed form factor operator product expansion. Our results are expected to give the maximally transcendental parts of the $gg\to Hg$ and $H\to ggg$ amplitudes in the heavy-top limit of QCD. At two loops, the extended-Steinmann-like space of functions we describe contains all transcendental functions required for four-point amplitudes with one massive and three massless external legs, and all massless internal lines, including processes such as $gg\to Hg$ and ${\gamma }^{\ast }\to q\bar{q}g$. We expect the extended-Steinmann-like space to contain these amplitudes at higher loops as well, although not to arbitrarily high loop order. We present evidence that the planar $\mathcal{N}=4$ three-point form factor can be placed in an even smaller space of functions, with no independent $\zeta$ values at weights two and three.

    ↳ hep-thhep-phJHEP(2021)·93 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.