Wed·Sep 2, 2020Wednesday·September 2, 2020

1. 01*

   Anatomy of inclusive $t\overline{t}W$ production at hadron colliders

   Stefan von Buddenbrock🇿🇦 · Richard Ruiz🇧🇪 · Bruce Mellado🇿🇦

   In LHC searches for new and rare phenomena the top-associated channel $pp\to t\overline{t}{W}^{\pm }+X$ is a challenging background that multilepton analyses must overcome. Motivated by sustained measurements of enhanced rates of same-sign and multi-lepton final states, we reexamine the importance of higher jet multiplicities in $pp\to t\overline{t}{W}^{\pm }+X$ that enter at $\mathcal{O}({\alpha }_s^3\alpha )$ and $\mathcal{O}({\alpha }_s^4\alpha )$, i.e., that contribute at NLO and NNLO in QCD in inclusive $t\overline{t}{W}^{\pm }$ production. Using fixed-order computations, we estimate that a mixture of real and virtual corrections at $\mathcal{O}({\alpha }_s^4\alpha )$ in well-defined regions of phase space can arguably increase the total $t\overline{t}{W}^{\pm }$ rate at NLO by at least $10\%-14\%$. However, by using non-unitary NLO multi-jet matching, we estimate that these same corrections are at most $10\%-12\%$, and at the same time exhibit the enhanced jet multiplicities that are slightly favored by data. This seeming incongruity suggests a need for the full NNLO result. We comment on implications for the $t\overline{t}Z$ process.

   hep-phhep-exPLB(2020)·72 citations
2. 02*

   The cosmic QCD transition for large lepton flavour asymmetries

   Mandy M. Middeldorf-Wygas🇩🇪 · Isabel M. Oldengott🇪🇸 · Dietrich Bödeker🇩🇪 · Dominik J. Schwarz🇩🇪

   We study the impact of large lepton flavour asymmetries on the cosmic QCD transition. Scenarios of unequal lepton flavour asymmetries are observationally almost unconstrained and therefore open up a whole new parameter space for the cosmic QCD transition. We find that for large asymmetries the formation of a Bose-Einstein condensate of pions can occur and identify the corresponding parameter space. In the vicinity of the QCD transition scale, we express the pressure in terms of a Taylor expansion with respect to the complete set of chemical potentials. The Taylor coefficients rely on input from lattice QCD calculations from the literature. The domain of applicability of this method is discussed.

   hep-phastro-ph.COhep-latPRD(2022)·48 citations
3. 03*

   Open charm and dileptons from relativistic heavy-ion collisions

   Elena Bratkovskaya🇩🇪 · Taesoo Song🇩🇪 · Pierre Moreau🇺🇸 · Carsten Greiner🇩🇪

   We study the dynamics of open charm production and the dilepton radiation of the semi-leptonic decays of correlated $D\bar{D}$ pairs versus the quark-gluon plasma (QGP) radiation and hadronic sources in relativistic heavy-ion collisions. Our study is based on the Parton-Hadron-String Dynamics (PHSD) transport approach employing a non-perturbative QCD description of the strongly interacting quark-gluon plasma (sQGP) in terms of dynamical quasiparticles and the EoS based on lattice QCD. We compare the PHSD results for charm observables with the calculations from BAMPS (Boltzmann Approach to Multi-Parton Scatterings) which is based on perturbative QCD with massless partons and interaction cross sections calculated in leading order of the QCD coupling. We compare the $p_T$ dependence of the ratio $R_{AA}$ of $D$-mesons in $A+A$ over $p+p$ collisions scaled by the number of binary collisions $N_{bin}$ as well as the elliptic flow $v_2$ of $D$-mesons calculated within the PHSD and BAMPS at LHC energies. In other study, based on the PHSD calculations we find that the dileptons from correlated $D-$meson semi-leptonic decays dominate the 'thermal' radiation from the QGP in central Pb+Pb collisions at the intermediate masses ($1.2<M<3$ GeV) for higher invariant energies However, for invariant energies $\sqrt{s_{NN}}<40$ GeV the QGP radiation overshines the contribution from $D,\bar{D}$ decays such that one should observe a rather clear signal from the partonic dilepton radiation. This finding provides promising perspectives to measure the QGP radiation in the dilepton experiments at RHIC BES and the future FAIR/NICA facilities.

   hep-phhep-exnucl-th1 citation
4. 04*

   Chiral oscillations in the non-relativistic regime

   Victor A. S. V. Bittencourt🇩🇪 · Alex E. Bernardini🇧🇷 · Massimo Blasone🇮🇹

   Massive Dirac particles are a superposition of left and right chiral components. Since chirality is not a conserved quantity, the free Dirac Hamiltonian evolution induces chiral quantum oscillations, a phenomenon related to the \textit{Zitterbewegung}, the trembling motion of free propagating particles. While not observable for particles in relativistic dynamical regimes, chiral oscillations become relevant when the particle's rest energy is comparable to its momentum. In this paper, we quantify the effect of chiral oscillations on the non-relativistic evolution of a particle state described as a Dirac bispinor and specialize our results to describe the interplay between chiral and flavor oscillations of non-relativistic neutrinos: we compute the time-averaged survival probability and observe an energy-dependent depletion of the quantity when compared to the standard oscillation formula. In the non-relativistic regime, this depletion due to chiral oscillations can be as large as 40$\%$. Finally, we discuss the relevance of chiral oscillations in upcoming experiments which will probe the cosmic neutrino background.

   hep-phquant-phEPJC(2021)·24 citations
5. 05*

   Use and reuse of SMEFT

   André David🇨🇭 · Giampiero Passarino🇮🇹

   In this work we address three questions: can we successfully describe (observed) deviations from the standard model in the SMEFT language? Can we learn something about the underlying, beyond the standard model, physics using the SMEFT language? If no deviation is observed, how to proceed? Given the myriad of viable BSM options with extended scalar sectors, we suggest a widespread use of SMEFT not just as a global fitting tool (that could miss out on deviations from extended scalar sectors) but also as a bookkeeping framework in which the results from SMEFT fits to individual observables are provided, reported, and archived in a consistent way. The compatibility of such individual results can then be assessed in the light of BSM models with extended scalar sectors.

   hep-phhep-ex19 citations
6. 06*

   An Attention Based Neural Network for Jet Tagging

   Jing Li🇨🇳 · Hao Sun🇨🇳

   Convolutional neural networks are basic structures using jet images as input for the jet tagging problems. However, what they have learned during the training process is always difficult to understand just through feature maps. Inspired by the attention mechanism popular in machine learning fields, we propose a novel attention-based neural network (ABNN) to get insight of this problem. The ABNN combines a jet image with average jet images from the signal and the background to generate attention maps which show clearly the relevant importance according to the different origination of jets. Compared with networks in the similar architecture, this network achieves better performance, which indicates the potential of attention mechanism to use in other works.

   hep-phhep-ex17 citations
7. 07*

   Tetra- and penta-quark structures in the constituent quark model

   Gang Yang🇨🇳 · Jialun Ping🇨🇳 · Jorge Segovia🇪🇸

   With the development of high energy physics experiments, a large amount of exotic states in the hadronic sector have been observed. In order to shed some insights on the nature of the tetraquark and pentaquark candidates, a constituent quark model, along with the gaussian expansion method, has been employed systematically in the real- and complex-range investigations. We review herein the double- and full-heavy tetraquarks, but also the hidden-charm, -bottom and doubly charmed pentaquarks. Several experimentally observed exotic hadrons are well reproduced within our approach; moreover, their possible compositeness are suggested and other properties analyzed accordingly such as their decay widths and general patterns in the spectrum. Besides, we report also some predictions not yet seen by experiment within the studied tetraquark and pentaquark sectors.

   hep-phhep-exSymmetry(2020)·162 citations
8. 08*

   Fermion mass hierarchies from supersymmetric gauged flavour symmetry in 5D

   Ketan M. Patel🇮🇳

   A mechanism to generate realistic fermion mass hierarchies based on supersymmetric gauged $U(1{)}_F$ symmetry in flat five-dimensional (5D) spacetime is proposed. The fifth dimension is compactified on $S^1/Z_2$ orbifold. The standard model fermions charged under the extra abelian symmetry along with their superpartners live in the 5D bulk. Bulk masses of fermions are generated by the vacuum expectation value of $N=2$ superpartner of $U(1{)}_F$ gauge field, and they are proportional to $U(1{)}_F$ charges of respective fermions. This decides localization of fermions in the extra dimension, which in turn gives rise to exponentially suppressed Yukawa couplings in the effective 4D theory. Anomaly cancellation puts stringent constraints on the allowed $U(1{)}_F$ charges which leads to correlations between the masses of quarks and leptons. We perform an extensive numerical scan and obtain several solutions for anomaly-free $U(1{)}_F$, which describe the observed pattern of fermion masses and mixing with all the fundamental parameters of order unity. It is found that the possible existence of SM singlet neutrinos substantially improves the spectrum of solutions by offering more freedom in choosing $U(1{)}_F$ charges. The model predicts $Z^{\prime }$ boson mediating flavour violating interactions in both the quark and lepton sectors with the couplings which can be explicitly determined from the Yukawa couplings.

   hep-phSciPost Phys.(2021)·3 citations
9. 09*

   Determination of ${\alpha }_S$ beyond NNLO using event shape averages

   Adam Kardos🇭🇺 · Gábor Somogyi🇭🇺 · Andrii Verbytskyi🇩🇪

   We consider a method for determining the QCD strong coupling constant using fits of perturbative predictions for event shape averages to data collected at the LEP, PETRA, PEP and TRISTAN colliders. To obtain highest accuracy predictions we use a combination of perturbative $\mathcal{O}({\alpha }_S^3)$ calculations and estimations of the $\mathcal{O}({\alpha }_S^4)$ perturbative coefficients from data. We account for non-perturbative effects using modern Monte Carlo event generators and analytic hadronization models. The obtained results show that the total precision of the ${\alpha }_S$ determination cannot be improved significantly with the higher order perturbative QCD corrections alone, but primarily requires a deeper understanding of the non-perturbative effects.

   hep-phEPJC(2021)·19 citations
10. 10*

    Pion quasiparticles and QCD phase transitions at finite temperature and isospin density from holography

    Xuanmin Cao🇨🇳 · Hui Liu🇨🇳 · Danning Li🇨🇳

    Spectra of pions, which are known as the pseudo-Goldstone bosons of spontaneous chiral symmetry breaking, as well as their relationship with chiral phase transition and pion superfluidity phase transition, have been investigated in the framework of soft-wall AdS/QCD. In chiral limit, it is proved both numerically and analytically that pions are massless Goldstone bosons even at finite temperature, which was usually considered as an assumption in soft-wall models. Above $T_c$, at which chiral condensate $⟨\bar{q}q⟩$ vanishes, the spectra of pions and scalar mesons merge together, showing the evidence of the restored chiral symmetry in hadronic spectrum level. Extending to finite quark mass, pion masses increase with quark mass. Further, it is more interesting to observe that the pole masses of pions decrease with temperature below $T_c$, which agrees with the analysis in Phys.Rev.Lett.88(2002)202302. Meanwhile, symmetry restoration above $T_c$ could be seen in the spectra of scalar and pseudo-scalar mesons. With finite temperature and isospin chemical potential ${\mu }_I$, it is shown that the masses of charged pions would split. The mass of positive charged pion ${\pi }^{+}$ decreases almost linearly to zero when ${\mu }_I$ grows to ${\mu }_I^c$, where pion condensation starts to form. This reveals the Goldstone nature of ${\pi }^{+}$ after pion superfluidity transition, which are closely related to the experimental observation.

    hep-phhep-thPRD(2020)·23 citations
11. 11*

    Energy and angular distributions of the bottom quark in the electron-positron annihilation $e^{+}{e}^{-}\to b{W}^{+}\bar{t}$

    I.V. Truten🇺🇦 · A.Yu. Korchin🇺🇦

    The distributions of the bottom quark in the process $e^{+}{e}^{-}\to t\bar{t}\to b{W}^{+}\bar{t}$ are considered at the $e^{+}{e}^{-}$ energy corresponding to the first construction stage of the Compact Linear Collider. The cross sections of $e^{+}{e}^{-}\to b\dots$, as functions of the $b$-quark energy and angle with respect to the direction of the electron beam, are derived and calculated. The effects of physics beyond the Standard Model are included via the modified $\gamma t\bar{t}$ and $Zt\bar{t}$ couplings which naturally appear in effective field theories. In addition to the cross sections, the energy and angular asymmetries are calculated. The dependence of these observables on the $e^{+}{e}^{-}$ energy is calculated, and features of this dependence are investigated.

    hep-phInt.J.Mod.Phys.A(2021)·1 citation
12. 12*

    $D^{\ast }$ Polarization as an Additional Constraint on New Physics in the $b\to c\tau {\bar{\nu }}_{\tau }$ Transition

    Mikhail A. Ivanov🇷🇺 · Jürgen G. Körner🇩🇪 · Pietro Santorelli🇮🇹 · Chien-Thang Tran🇮🇹

    Measurements of the branching fractions of the semileptonic decays $B\to D^{(\ast )}\tau {\bar{\nu }}_{\tau }$ and $B_c\to J/\psi \tau {\bar{\nu }}_{\tau }$ systematically exceed the Standard Model (SM) predictions, pointing to possible signals of new physics that can violate lepton flavor universality. The unknown origin of new physics realized in these channels can be probed using a general effective Hamiltonian constructed from four-fermion operators and the corresponding Wilson coefficients. Previously, constraints on these Wilson coefficients were obtained mainly from the experimental data for the branching fractions. Meanwhile, polarization observables were only theoretically studied. The situation has changed with more experimental data having become available, particularly those regarding the polarization of the tau and the $D^{\ast }$ meson. In this study, we discuss the implications of the new data on the overall picture. We then include them in an updated fit of the Wilson coefficients using all hadronic form factors from our covariant constituent quark model. The use of our form factors provides an analysis independent of those in the literature. Several new-physics scenarios are studied with the corresponding theoretical predictions provided, which are useful for future experimental studies.

    hep-phParticles(2020)·14 citations
13. 13*

    Constraining light dark matter upscattered by ultrahigh-energy cosmic rays

    Chen Xia🇨🇳 · Yan-Hao Xu🇨🇳 · Yu-Feng Zhou🇨🇳

    Light halo dark matter (DM) particles upscattered by high-energy cosmic rays (CRs) can be energetic, and become detectable by conventional direct detection experiments. The current constraints derived from space-based direct CR measurements can reach $\mathcal{O}(10^{-31}){\text{ cm}}^2$ for a constant DM-nucleon scattering cross section. We show that if the CR energy spectrum follows a power law of type $\sim E^{-3}$, the derived constraints on the scattering cross section will be highly insensitive to DM particle mass. This suggests that ultrahigh-energy CRs (UHECRs) indirectly measured by ground-based detectors can be used to place constraints on ultralight DM particles, as $E^{-3}$ is a very good approximation of the UHECR energy spectrum up to energy $\sim 10^{20}\text{ eV}$. Using the recent UHECR flux data, we show that the current constraints derived from space-based CR measurements can in principle be extended to ultralight DM particles far below eV scale.

    hep-phastro-ph.CONPB(2021)·50 citations
14. 14*

    Quantum coherence to interstellar distances

    Arjun Berera🇬🇧

    Quantum coherence could be sustained up to interstellar distances. It is shown that the photon mean free path in certain regions of the electromagnetic spectrum, such as within the radio or x-ray ranges, could allow sustaining of the quantum state of a photon up to galactic distances. Therefore processes involving quantum entanglement, such as quantum teleportation, could be realized over very long distances in the Milky Way or other galaxies. This is of fundamental interest and offers a new direction in the role of quantum mechanics. Some limited applications of this observation are discussed.

    hep-phastro-ph.GAquant-phPRD(2020)·17 citations
15. 15*

    NLO QCD and EW corrections to vector-boson scattering into ZZ at the LHC

    Ansgar Denner🇩🇪 · Robert Franken🇩🇪 · Mathieu Pellen🇬🇧 · Timo Schmidt🇩🇪

    We present the first calculation of the full next-to-leading-order electroweak and QCD corrections for vector-boson scattering (VBS) into a pair of Z bosons at the LHC. We consider specifically the process $\mathrm{pp}\to {\mathrm{e}}^{+}{\mathrm{e}}^{-}{\mu }^{+}{\mu }^{-}\mathrm{jj}+X$ at orders $\mathcal{O}({\alpha }^7)$ and $\mathcal{O}({\alpha }_s{\alpha }^6)$ and take all off-shell and interference contributions into account. Owing to the presence of enhanced Sudakov logarithms, the electroweak corrections amount to $-16\%$ of the leading-order electroweak fiducial cross section and induce significant shape distortions of differential distributions. The QCD corrections on the other hand are larger ($+24\%$) than typical QCD corrections in VBS. This originates from considering the full computation including tri-boson contributions in a rather inclusive phase space. We also provide a leading-order analysis of all contributions to the cross section for $\mathrm{pp}\to {\mathrm{e}}^{+}{\mathrm{e}}^{-}{\mu }^{+}{\mu }^{-}\mathrm{jj}+X$ in a realistic setup.

    hep-phJHEP(2020)·52 citations
16. 16*

    Collider Physics at the Precision Frontier

    Gudrun Heinrich🇩🇪

    The precision frontier in collider physics is being pushed at impressive speed, from both the experimental and the theoretical side. The aim of this review is to give an overview of recent developments in precision calculations within the Standard Model of particle physics, in particular in the Higgs sector. While the first part focuses on phenomenological results, the second part reviews some of the techniques which allowed the rapid progress in the field of precision calculations. The focus is on analytic and semi-numerical techniques for multi-loop amplitudes, however fully numerical methods as well as subtraction schemes for infrared divergent real radiation beyond NLO are also briefly described.

    hep-phPhys.Rept.(2021)·219 citations
17. 17*

    Unveiling the transverse formation length of nonlinear Compton scattering

    A. Di Piazza🇩🇪

    The process of emission of electromagnetic radiation does not occur instantaneously but it is "formed" over a finite time known as radiation formation time. In the ultrarelativistic regime, the corresponding (longitudinal) formation length is given by the formation time times the speed of light and controls several features of radiation. Here, we elucidate the importance of the transverse formation length (TFL) by investigating nonlinear Compton scattering by an electron initially counterpropagating with respect to a \emph{flying focus} laser beam. The TFL is related to the transverse size of the radiation formation "volume" and, unlike the longitudinal formation length, has a quantum origin. Being the TFL typically of the order of the Compton wavelength, where any laser field can be assumed to be approximately uniform, related quantum interference effects have been ignored. However, we show analytically that if the focus in a flying focus beam with $n_L\gg 1$ cycles moves at the speed of light and backwards with respect to the beam propagation direction, the effects of the TFL undergo a large enhancement proportional to $n_L$ and may substantially alter the differential emission probability for feasible flying focus pulses.

    hep-phPRA(2021)·22 citations
18. 18*

    String shoving effects on jets in p-p collisions

    Smita Chakraborty🇸🇪

    Di-jet observables are excellent probes to study the effect of jets in dense systems. Interacting Lund strings will affect jet observables and suggests a new common mechanism responsible for jet modification in p-A and A-A. In this proceeding, we present our new implementation of the string shoving mechanism in PYTHIA8 which lets us study the effects on jet observables in p-p and nuclear collisions. We also present preliminary results showing the effects in hadron-jet correlation studies.

    hep-phPoS(2021)·2 citations
19. 19*

    Probing new physics with the kaon decays $K\to \pi \pi /E$

    Chao-Qiang Geng🇨🇳 · Jusak Tandean🇹🇼

    The latest search for the rare kaon decay $K^{+}\to {\pi }^{+}\nu \bar{\nu }$ by the NA62 experiment has produced evidence for it with a branching fraction consistent with the prediction of the standard model. The new result implies that in this decay, with the $\nu \bar{\nu }$ pair appearing as missing energy ($/E$), the room for possible new physics is no longer sizable and that therefore its contributions to underlying four-particle $s\to d/E$ operators with parity-even $ds$ quark bilinears have become significantly constrained. Nevertheless, we point out that appreciable manifestations from beyond the standard model induced by the corresponding operators with mainly parity-odd $ds$ quark bilinears could still occur in $K\to \pi \pi /E$ modes, on which there are only minimal empirical details at present. We find in particular that new physics of this kind may enhance the branching fraction of $K_L\to {\pi }^0{\pi }^0/E$ to values reaching its current experimental upper limit and the branching fractions of $K^{+}\to {\pi }^{+}{\pi }^0/E$ and $K_L\to {\pi }^{+}{\pi }^{-}/E$ to the levels of $10^{-7}$ and $10^{-6}$, respectively. Thus, quests for these decays in existing kaon facilities such as KOTO and NA62 or future ones could provide valuable information complementary to that gained from $K\to \pi /E$.

    hep-phhep-exPRD(2020)·11 citations
20. 20*

    Study of anomalous gauge-Higgs couplings using $Z$ boson polarization at LHC

    Kumar Rao🇮🇳 · Saurabh D. Rindani🇮🇳 · Priyanka Sarmah🇮🇳

    We estimate model-independent bounds that could be obtained on the anomalous $ZZH$ vertex using polarization parameters of the $Z$ boson produced in the Higgstrahlung process at the LHC. We calculate the eight independent polarization parameters from the spin density matrix elements of the $Z$, which can probe underlying new physics contributions to $ZH$ production. By using the approach that connects these polarization observables to the coefficients in the angular distribution of the decay products of the $Z$, we estimate the limits on the anomalous $ZZH$ coupling that can be obtained at the 14 TeV LHC.

    hep-phNPB(2021)·18 citations
21. 21*

    InClass Nets: Independent Classifier Networks for Nonparametric Estimation of Conditional Independence Mixture Models and Unsupervised Classification

    Konstantin T. Matchev🇺🇸 · Prasanth Shyamsundar🇺🇸

    We introduce a new machine-learning-based approach, which we call the Independent Classifier networks (InClass nets) technique, for the nonparameteric estimation of conditional independence mixture models (CIMMs). We approach the estimation of a CIMM as a multi-class classification problem, since dividing the dataset into different categories naturally leads to the estimation of the mixture model. InClass nets consist of multiple independent classifier neural networks (NNs), each of which handles one of the variates of the CIMM. Fitting the CIMM to the data is performed by simultaneously training the individual NNs using suitable cost functions. The ability of NNs to approximate arbitrary functions makes our technique nonparametric. Further leveraging the power of NNs, we allow the conditionally independent variates of the model to be individually high-dimensional, which is the main advantage of our technique over existing non-machine-learning-based approaches. We derive some new results on the nonparametric identifiability of bivariate CIMMs, in the form of a necessary and a (different) sufficient condition for a bivariate CIMM to be identifiable. We provide a public implementation of InClass nets as a Python package called RainDancesVI and validate our InClass nets technique with several worked out examples. Our method also has applications in unsupervised and semi-supervised classification problems.

    ↳ stat.MLcs.LGecon.EMhep-ph+2Mach.Learn.Sci.Tech.(2022)·0 citations
22. 22*

    Simplifying $D$-Dimensional Physical-State Sums in Gauge Theory and Gravity

    Dimitrios Kosmopoulos🇺🇸

    We provide two independent systematic methods of performing $D$-dimensional physical-state sums in gauge theory and gravity in such a way so that spurious light-cone singularities are not introduced. A natural application is to generalized unitarity in the context of dimensional regularization or theories in higher spacetime dimensions. Other applications include squaring matrix elements to obtain cross sections, and decompositions in terms of gauge-invariant tensors.

    ↳ hep-thhep-phPRD(2022)·47 citations
23. 23*

    Enhancement of Lithium in Red Clump Stars by the Additional Energy Loss Induced by New Physics

    Kanji Mori🇯🇵 · Motohiko Kusakabe🇨🇳 · A. Baha Balantekin🇺🇸 · Toshitaka Kajino🇯🇵 · Michael A. Famiano🇺🇸

    Since 7Li is easily destroyed in low temperatures, the surface lithium abundance decreases as stars evolve. This is supported by the lithium depletion observed in the atmosphere of most red giants. However, recent studies show that almost all of red clump stars have high lithium abundances A(Li)>-0.9, which are not predicted by the standard theory of the low-mass stellar evolution. In order to reconcile the discrepancy between the observations and the model, we consider additional energy loss channels which may come from physics beyond the Standard Model. A(Li) slightly increases near the tip of the red giant branch even in the standard model with thermohaline mixing because of the 7Be production by the Cameron-Fowler mechanism, but the resultant 7Li abundance is much lower than the observed values. We find that the production of 7Be becomes more active if there are additional energy loss channels, because themohaline mixing becomes more efficient and a heavier helium core is formed.

    ↳ astro-ph.SRhep-phnucl-thMNRAS(2021)·10 citations
24. 24*

    Impact of the small-scale structure on the Stochastic Background of Gravitational Waves from cosmic strings

    Pierre G. Auclair🇫🇷

    Numerical simulations and analytical models suggest that infinite cosmic strings produce cosmic string loops of all sizes with a given power-law. Precise estimations of the power-law exponent are still matter of debate while numerical simulations do not incorporate all the radiation and back-reaction effects expected to affect the network at small scales. Previously it has been shown, using a Boltzmann approach, that depending on the steepness of the loop production function and the gravitational back-reaction scale, a so-called Extra Population of Small Loops (EPSL) can be generated in the loop number density. We propose a framework to study the influence of this extra population of small loops on the Stochastic Background of Gravitational Waves (SBGW). We show that this extra population can have a significant signature at frequencies higher than $H_0(\Gamma G\mu {)}^{-1}$ where $\Gamma$ is of order $50$ and $H_0$ is the Hubble constant. We propose a complete classification of the gravitational wave power spectra expected from cosmic strings into four classes, including the model of Blanco-Pillado, Olum and Shlaer and the model of Lorenz, Ringeval and Sakellariadou. Finally we show that given the uncertainties on the Polchinski-Rocha exponents, two hybrid classes of gravitational wave power spectrum can be considered giving very different predictions for the SBGW.

    ↳ astro-ph.COgr-qchep-phJCAP(2020)·16 citations
25. 25*

    New method for calculating electromagnetic effects in semileptonic beta-decays of mesons

    Chien-Yeah Seng🇩🇪 · Xu Feng🇨🇳 · Mikhail Gorchtein🇩🇪 · Lu-Chang Jin🇺🇸 · Ulf-G. Meißner🇩🇪

    We construct several classes of hadronic matrix elements and relate them to the low-energy constants in Chiral Perturbation Theory that describe the electromagnetic effects in the semileptonic beta decay of the pion and the kaon. We propose to calculate them using lattice QCD, and argue that such a calculation will make an immediate impact to a number of interesting topics at the precision frontier, including the outstanding anomalies in $|V_{us}|$ and the top-row Cabibbo-Kobayashi-Maskawa matrix unitarity.

    ↳ hep-lathep-exhep-phnucl-ex+1JHEP(2020)·38 citations
26. 26*

    Solar neutrino detection in liquid xenon detectors via charged-current scattering to excited states

    Scott Haselschwardt🇺🇸 · Brian Lenardo🇺🇸 · Pekka Pirinen🇫🇮 · Jouni Suhonen🇫🇮

    We investigate the prospects for real-time detection of solar neutrinos via the charged-current neutrino-nucleus scattering process in liquid xenon time projection chambers. We use a nuclear shell model, benchmarked with experimental data, to calculate the cross sections for populating specific excited states of the caesium nuclei produced by neutrino capture on ${}^{131}$Xe and ${}^{136}$Xe. The shell model is further used to compute the decay schemes of the low-lying $1^{+}$ excited states of ${}^{136}$Cs, for which there is sparse experimental data. We explore the possibility of tagging the characteristic de-excitation $\gamma$-rays/conversion electrons using two techniques: spatial separation of their energy deposits using event topology and their time separation using delayed coincidence. The efficiencies in each case are evaluated within a range of realistic detector parameters. We find that the topological signatures are likely to be dominated by radon backgrounds, but that a delayed coincidence signature from long-lived states predicted in ${}^{136}$Cs may enable background-free detection of CNO neutrino interactions in next-generation experiments with smaller uncertainty than current measurements. We also estimate the sensitivity as a function of exposure for detecting the solar-temperature-induced line shift in ${}^7$Be neutrino emission, which may provide a new test of solar models.

    ↳ hep-exhep-phphysics.ins-detPRD(2020)·19 citations
27. 27*

    Dark Matter Density Profiles in Dwarf Galaxies: Linking Jeans Modeling Systematics and Observation

    Laura J. Chang🇺🇸 · Lina Necib🇺🇸

    The distribution of dark matter in dwarf galaxies can have important implications on our understanding of galaxy formation as well as the particle physics properties of dark matter. However, accurately characterizing the dark matter content of dwarf galaxies is challenging due to limited data and complex dynamics that are difficult to accurately model. In this paper, we apply spherical Jeans modeling to simulated stellar kinematic data of spherical, isotropic dwarf galaxies with the goal of identifying the future observational directions that can improve the accuracy of the inferred dark matter distributions in the Milky Way dwarf galaxies. We explore how the dark matter inference is affected by the location and number of observed stars as well as the line-of-sight velocity measurement errors. We use mock observation to demonstrate the difficulty in constraining the inner core/cusp of the dark matter distribution with datasets of fewer than 10,000 stars. We also demonstrate the need for additional measurements to make robust estimates of the expected dark matter annihilation signal strength. For the purpose of deriving robust indirect detection constraints, we identify Ursa Major II, Ursa Minor, and Draco as the systems that would most benefit from additional stars being observed.

    ↳ astro-ph.COastro-ph.GAhep-phMNRAS(2021)·29 citations
28. 28*

    Nonperturbative quantization approach for QED on the Hopf bundle

    Vladimir Dzhunushaliev🇰🇿 · Vladimir Folomeev🇰🇬

    We consider the Dirac equation and Maxwell's electrodynamics in $\mathbb{R}\times S^3$ spacetime, where a three-dimensional sphere is the Hopf bundle $S^3\to S^2$. In both cases, discrete spectra of classical solutions are obtained. Based on the solutions obtained, the quantization of free, noninteracting Dirac and Maxwell fields is carried out. The method of nonperturbative quantization of interacting Dirac and Maxwell fields is suggested. The corresponding operator equations and the infinite set of the Schwinger-Dyson equations for Green's functions is written down. To illustrate the suggested scheme of nonperturbative quantization, we write a simplified set of equations describing some physical situation. Also, we discuss the properties of quantum states and operators of interacting fields.

    ↳ hep-thhep-phUniverse(2021)·0 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.