Mon·May 13, 2019Monday·May 13, 2019

1. 01*

   Light Mediators in Anomaly Free $U(1{)}_X$ Models I - Theoretical Framework

   F.C. Correia🇩🇪 · Svjetlana Fajfer🇸🇮

   We examine theoretical features of $U(1{)}_X$ extensions of the Standard Model whose quantum anomalies are canceled per generation. Similarly to other versions, the theory consists of a Two-Higgs-Doublet Model plus a scalar singlet embedded into the $SM\otimes U(1{)}_X$ gauge group, and introduces small modifications to the $Z$-boson interactions. These changes can be minimized by exclusively charging right-handed fermions under the new Abelian symmetry, and are compensated by the neutral $X$-boson exchange. Non-universality of fermion couplings can also be achieved by requiring one single $X$-charged family. In general, $X$ gauge bosons can be separated into $A^{\prime }$ (dark photons) and $Z^{\prime }$ subsets, distinguished by the presence of axial-vector currents. $A^{\prime }$ physics is commonly simpler to constrain and therefore favored by experimental tests. Finally, the model can be UV completed both by stable $\chi$ fermions or by right-handed neutrinos. The prior case may provide cold WIMPs in the theory.

   hep-phhep-thJHEP(2019)·13 citations
2. 02*

   Light Mediators in Anomaly Free $U(1{)}_X$ Models II - Constraints on Dark Gauge Bosons

   F.C. Correia🇩🇪 · Svjetlana Fajfer🇸🇮

   We consider experimental constraints in the MeV region in order to determine the parameter space for the $U(1{)}_X$ extension of the Standard Model, presented in the first part of our work. In particular, we focus on the model UV-completed by cold WIMPs. We conclude that the electron anomalous magnetic moment, the neutrino trident production and the relic abundance ${\Omega }_{CDM}$ provide the most stringent bounds and, in particular cases, they are sufficient to exclude dark-photon ($A^{\prime }$) models. By allowing the axial-vector coupling of the dark gauge boson $Z^{\prime }$, the interference effect with the SM gauge bosons may reduce the bounds coming from the trident neutrino production. At the same time, such coupling allows a region of the parameter space already favored both by the relic abundance and by the discrepancy between experimental result and theoretical prediction for the muon anomalous magnetic moment. We emphasize that light-$Z^{\prime }$ interactions, non-universal for the two first lepton families, necessarily create a difference in the proton charge radius measured in the Lamb shift of the $e$-hydrogen and $\mu$-hydrogen. Finally, we determine the effects of the new gauge boson on the forward-backward asymmetry in $e^{+}{e}^{-}\to \bar{f}f$, $f=\mu ,\tau$, and on the leptonic decays $M\to j{\nu }_j{l}^{+}{l}^{-}$, where $M=\pi ,K,D,D_s,B$ and $j,l=e,\mu$.

   hep-phhep-exJHEP(2019)·11 citations
3. 03*

   Production of exotic tetraquarks $QQ\bar{q}\bar{q}$ in heavy-ion collisions at the LHC

   C. E. Fontoura🇧🇷 · G. Krein🇧🇷 · A. Valcarce🇪🇸 · J. Vijande🇪🇸

   We investigate the production of exotic tetraquarks, $QQ\bar{q}\bar{q}\equiv T_{QQ}$ ($Q=c$ or $b$ and $q=u$ or $d$), in relativistic heavy-ion collisions using the quark coalescence model. The $T_{QQ}$ yield is given by the overlap of the density matrix of the constituents in the emission source with the Wigner function of the produced tetraquark. The tetraquark wave function is obtained from exact solutions of the four-body problem using realistic constituent models. The production yields are typically one order of magnitude smaller than previous estimations based on simplified wave functions for the tetraquarks. We also evaluate the consequences of the partial restoration of chiral symmetry at the hadronization temperature on the coalescence probability. Such effects, in addition to increasing the stability of the tetraquarks, lead to an enhancement of the production yields, pointing towards an excellent discovery potential in forthcoming experiments. We discuss further consequences of our findings for the search of exotic tetraquarks in central Pb+Pb collisions at the LHC.

   hep-phnucl-thPRD(2019)·38 citations
4. 04*

   Constraints on the Higgs boson anomalous FCNC interactions with light quarks

   M.Ilyushin🇷🇺 · P.Mandrik🇷🇺 · S.Slabospitsky🇷🇺

   We consider the Higgs boson anomalous FCNC interactions with $u$, $c$, $d$, $s$ and $b$ quarks using the effective field theory framework. Constraints on anomalous couplings are derived from experimental results on Higgs boson production with subsequent decay into $b\bar{b}$ pair at LHC with $\sqrt{s}=13$~TeV. Upper limits on the branching fractions of $H\to b\bar{s}$ and $H\to b\bar{d}$ are set by performing a realistic detector simulation and accurately reproducing analysis selections of the CMS Higgs boson measurement in the four-lepton final state at $\sqrt{s}=13$ TeV. The searches are projected into operation conditions of HL-LHC. Sensitivity at FCC-hh to anomalous FCNC interactions is studied based on Higgs boson production with $H\to \gamma \gamma$ decay channel. It is shown that at FCC-hh machine one can expect to set the upper limits of the order of $10^{-2}$ at $95\%$ CL for $\mathcal{B}(H\to b\bar{s})$ and $\mathcal{B}(H\to b\bar{d})$.

   hep-phhep-exNPB(2020)·6 citations
5. 05*

   Probing signatures of beyond standard model physics through $B_s^{\ast }\to {\mu }^{+}{\mu }^{-}$ decay

   Jyoti Saini🇮🇳 · Dinesh Kumar🇮🇳 · Shireen Gangal🇮🇳 · S. B. Das🇮🇳

   We perform a model independent analysis to identify new physics operators which can enhance the branching ratio of $B_s^{\ast }\to {\mu }^{+}{\mu }^{-}$ above its Standard Model (SM) prediction. We find that none of the new physics operators which provide a good fit to $b\to s{\mu }^{+}{\mu }^{-}$ data can enhance the Br($B_s^{\ast }\to {\mu }^{+}{\mu }^{-}$) above its SM value.

   hep-phSpringer Proc.Phys.(2019)·1 citation
6. 06*

   Polarisation at NLO in WZ production at the LHC

   Julien Baglio🇩🇪 · Le Duc Ninh🇻🇳

   The pair production of a $W$ and a $Z$ boson at the LHC is an important process to study the triple-gauge boson couplings as well as to probe new physics that could arise in the gauge sector. In particular the leptonic channel $pp\to W^{\pm }Z\to 3\ell +\nu +X$ is considered by ATLAS and CMS collaborations. Polarisation observables can help pinning down new physics and give information on the spin of the gauge bosons. Measuring them requires high statistics as well as precise theoretical predictions. We define in this contribution fiducial polarisation observables for the $W$ and $Z$ bosons and we present theoretical predictions in the Standard Model at next-to-leading order (NLO) including QCD as well as NLO electroweak corrections, the latter in the double-pole approximation. We also show that this approximation works remarkably well for $W^{\pm }Z$ production at the LHC by comparing to the full results.

   hep-phhep-ex1 citation
7. 07*

   Electromagnetic form factors of the baryon decuplet with flavor SU(3) symmetry breaking

   June-Young Kim🇰🇷 · Hyun-Chul Kim🇰🇷

   We investigate the electromagnetic form factors of the baryon decuplet within the framework of the $\mathrm{SU}(3)$ self-consistent chiral quark-soliton model, taking into account the $1/N_c$ rotational corrections and the effects of flavor $\mathrm{SU}(3)$ symmetry breaking. We first examine the valence- and sea-quark contributions to each electromagnetic form factor of the baryon decuplet and then the effects of the flavor SU(3) symmetry breaking. The present results are in good agreement with the recent lattice data. We also compute the charge radii, the magnetic radii, the magnetic dipole moments and the electric quadrupole moments, comparing their results with those from other theoretical works. We also make a chiral extrapolation to compare the present results with the lattice data in a more quantitative manner. The results show in general similar tendency to the lattice results. In particular, the results of the $M1$ and $E2$ form factors are in good agreement with those of lattice QCD.

   hep-phhep-exEPJC(2019)·23 citations
8. 08*

   A unified explanation of $b\to s{\mu }^{+}{\mu }^{-}$ anomalies, neutrino masses and $B\to \pi K$ puzzle

   Alakabha Datta🇺🇸 · Divya Sachdeva🇮🇳 · John Waite🇺🇸

   Anomalies in semi-leptonic $B$ decays could indicate new physics beyond the standard model(SM). There is an older puzzle in non-leptonic $B\to \pi K$ decays. The new particles, leptoquarks and diquarks, required to solve the semi-leptonic and the non-leptonic puzzles can also generate neutrino masses and mixing at loop level. We show that a consistent framework to explain the $B$ anomalies and the neutrino masses is possible and we make predictions for certain rare nonleptonic $B$ decays.

   hep-phPRD(2019)·28 citations
9. 09*

   Constraints on scalar and vector leptoquarks from the LHC Higgs data

   Jian Zhang🇨🇳 · Chong-Xing Yue🇨🇳 · Chun-Hua Li🇨🇳 · Shuo Yang🇨🇳

   We study contributions of single scalar or vector leptoquark (LQ) to loop-induced Higgs processes, gluon fusion production ($gg\to h$) and $h\to \gamma \gamma$ decay, by analyzing the current Higgs data from the LHC Run I and II. Scalar LQ is studied in a model independent way, while the vector LQ $U_1(3,1,2/3)$ is discussed in the '4321' model. Constraints on the interactions of LQ and Higgs boson are obtained. We provide a method to determine vacuum expectation values ${\upsilon }_3$ and ${\upsilon }_1$ of the new scalar fields ${\Omega }_3$ and ${\Omega }_1$ in the '4321' model via the combination of Higgs data and measurements of $R_{D^{(\ast )}}$ and $R_{K^{(\ast )}}$.

   hep-phhep-ex16 citations
10. 10*

    The hidden charm pentaquark states and ${\Sigma }_c{\bar{D}}^{(\ast )}$ interaction in chiral perturbation theory

    Lu Meng🇨🇳 · Bo Wang🇨🇳 · Guang-Juan Wang🇨🇳 · Shi-Lin Zhu🇨🇳

    In this work, we employ the heavy hadron chiral perturbation theory (HHChPT) to calculate the ${\Sigma }_c{\bar{D}}^{(\ast )}$ potentials to the next-to-leading order. The contact, the one-pion exchange and the two-pion exchange interactions are included. Besides, the mass splittings between the heavy quark spin symmetry (HQSS) multiplets are kept in calculations. Our result shows that neglecting the heavy quark symmetry (HQS) violation effect may be misleading to predict the potentials between the charmed hadrons. We perform numerical analysis with three scenarios. In the first scenario, we relate the low-energy constants (LECs) in the contact terms of ${\Sigma }_c{\bar{D}}^{(\ast )}$ to those of nucleon systems, and reproduce the $P_c(4312)$ and $P_c(4440)$ as loosely bound states. In the second scenario, we vary the unknown LECs and find a small parameter region in which $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ can coexist as molecular states. In the third scenario, we include the coupled-channel effect on the basis of scenario II, and notice that the three $P_c$ states can be reproduced as molecular states simultaneously in a large region of parameters. Our analytical results can be used for the chiral extrapolations in lattice QCD. With the lattice QCD results in the future as inputs, the identification of the $P_c$ states and predictions for other systems would be more reliable.

    hep-phhep-exhep-latnucl-thPRD(2019)·139 citations
11. 11*

    Precision analysis of pseudoscalar interactions in neutron beta decays

    A. N. Ivanov🇦🇹 · R. Höllwieser🇦🇹 · N. I. Troitskaya🇦🇹 · M. Wellenzohn🇦🇹 · Ya. A. Berdnikov🇷🇺

    We analyze the contributions of the one-pion-pole (OPP) exchange, caused by strong low-energy interactions, and the pseudoscalar interaction beyond the Standard Model (BSM) to the correlation coefficients of the neutron beta-decays for polarized neutrons, polarized electrons and unpolarized protons. The strength of contributions of pseudoscalar interactions is defined by the effective coupling constant C_ps = C^(OPP)_ps + C^(BSM)_ps. We show that the contribution of the OPP exchange is of order C^(OPP)_ps ~ - 10^(-5). The effective coupling constant C^(BSM)_ps of the pseudoscalar interaction BSM can be in principle complex. Using the results, obtained by Gonzalez-Alonso et al.( Prog. Part. Nucl. Phys. 104, 165 (2019)) we find that the values of the real and imaginary parts of the effective coupling constant C^(BSM)_ps are constrained by - 3.5x10^{-5} < ReC^(BSM)_ps < 0 and ImC^(BSM)_ps < - 2.3x10^(-5), respectively. The obtained results can be used as a theoretical background for experimental searches of contributions of interactions BSM in asymmetries of the neutron beta-decays with a polarized neutron, a polarized electron and an unpolarized proton at the level of accuracy of a few parts of $10^{-5}$ or even better (Abele, Hyperfine Interact.237, 155 (2016)).

    hep-phgr-qcnucl-exNPB(2020)·9 citations
12. 12*

    Probing the inert doublet model using jet substructure with a multivariate analysis

    Akanksha Bhardwaj🇮🇳 · Partha Konar🇮🇳 · Tanumoy Mandal🇸🇪 · Soumya Sadhukhan🇮🇳

    We explore the challenging but phenomenologically interesting hierarchical mass spectrum of the Inert Doublet Model where relatively light dark matter along with much heavier scalar states can fully satisfy the constraints on the relic abundance and also fulfill other theoretical as well as collider and astrophysical bounds. To probe this region of parameter space at the LHC, we propose a signal process that combines up to two large radius boosted jets along with substantial missing transverse momentum. Aided by our intuitive signal selection, we capture a hybrid process where the di-fatjet signal is significantly enhanced by the mono-fatjet contribution with minimal effects on the SM di-fatjet background. Substantiated by the sizable mass difference between the scalars, these boosted jets, originally produced from the hadronic decay of massive vector bosons, still carry the inherent footprint of their root. These features implanted inside the jet substructure can provide additional handles to deal with a large background involving QCD jets. We adopt a multivariate analysis using boosted decision tree to provide a robust mechanism to explore the hierarchical scenario, which would bring almost the entire available parameter space well within reach of the 14 TeV LHC runs with high luminosity.

    hep-phhep-exPRD(2019)·34 citations
13. 13*

    Internal particle width effects on the the triangle singularity mechanism in the study of the $\eta (1405)$ and $\eta (1475)$ puzzle

    Meng-Chuan Du🇨🇳 · Qiang Zhao🇨🇳

    In this article, the analyticity of triangle loop integral with complex masses of internal particles is discussed in a new perspective, base on which we obtain the explicit width dependence of the absorptive part of the triangle amplitude. We reanalyze the decay pattern of $\eta (1405/1475)$ with the width effects included in the triangle singularity (TS) mechanism. Based on the present experimental information, we provide a self-consistent description of the $K\bar{K}\pi$, $\eta \pi \pi$, and $3\pi$ decay channels for $\eta (1405/1475)$. Our results confirm the claim that the TS mechanism plays a decisive role in the understanding of the $\eta (1405)$ and $\eta (1475)$ puzzle. Namely, the observed differences of $\eta$ resonances within the mass region of $1.40\sim 1.48$ GeV are originated from the same state. For the isospin violated process $J/\psi \to \gamma \eta (1405/1475)\to f_0(980)\pi \to 3\pi$, we identify an additional contribution to the $a_0(980)-f_0(980)$ mixing via the TS mechanism.

    hep-phhep-exnucl-thPRD(2019)·45 citations
14. 14*

    Minimal asymptotically safe dark matter

    Chengfeng Cai🇨🇳 · Hong-Hao Zhang🇨🇳

    We study a simple class of dark matter models with N_f copies of electroweak fermionic multiplets, stabilized by O(N_F) global symmetry. Unlike conventional minimal dark matter which usually suffers from Landau poles, in these models the gauge coupling g_2 has a non-trivial ultraviolet fixed point, and thus is asymptotically safe as long as N_F is large enough. These fermionic n-plet models have only two free parameters: N_F and a common mass M_DM, which relate to dark matter relic abundance. We find that the mass of triplet fermionic dark matter with N_F being dozens of flavors can be several hundred GeV, which is testable on LHC. A benefit of large N_F is that DM pair annihilation rate in dwarf galaxies is effectively suppressed by 1/N_F, and thus they can evade the constraint from gamma-ray continuous spectrum observation. For the case of triplets, we find that the models in the range 3 <= N_F <= 20 are consistent with all current experiments. However, for N_F quintuplets, even with large N_F they are still disfavored by the gamma-ray continuous spectrum.

    hep-phastro-ph.COPLB(2019)·9 citations
15. 15*

    Unification of the Standard Model and Dark Matter Sectors in [SU(5)$\times$U(1)]${}^4$

    Ayuki Kamada🇰🇷 · Masaki Yamada🇺🇸 · Tsutomu T. Yanagida🇯🇵

    A simple model of dark matter contains a light Dirac field charged under a hidden U(1) gauge symmetry. When a chiral matter content in a strong dynamics satisfies the t'Hooft anomaly matching condition, a massless baryon is a natural candidate of the light Dirac field. One realization is the same matter content as the standard SU(5)$\times$U(1)${}_{(B-L)}$ grand unified theory. We propose a chiral [SU(5)$\times$U(1)]${}^4$ gauge theory as a unified model of the SM and DM sectors. The low-energy dynamics, which was recently studied, is governed by the hidden U(1)${}_4$ gauge interaction and the third-family U(1)${}_{(B-L{)}_3}$ gauge interaction. This model can realize self-interacting dark matter and alleviate the small-scale crisis of collisionless cold dark matter in the cosmological structure formation. The model can also address the semi-leptonic $B$-decay anomaly reported by the LHCb experiment.

    hep-phastro-ph.COJHEP(2019)·8 citations
16. 16*

    Revealing mass-degenerate states in Higgs boson signals

    Shehu AbdusSalam🇮🇷 · Maria Eugenia Cabrera🇬🇹

    The observed Higgs boson signals to-date could be due to having two quasi-degenerate 125 GeV scalar states in Nature. This kind of scenario tallies well with the predictions from the Next-to-Minimal Supersymmetric Standard Model (NMSSM). We have analysed the phenomenological NMSSM Higgs boson couplings and derived a parameterization of the signal strengths within the two quasi-degenerate framework. With essentially two parameters, it is shown that the combined strengths of the two quasi-degenerate Higgs states in the leptonic (and b-quark) decay channels depart from the Standard Model values in the opposite direction to those in the vector boson channels. We identify experimental measurements for distinguishing a single from a double Higgs scenarios. The proposed parameterization can be used for benchmarking studies towards establishing the status of quasi-degenerate Higgs scenarios.

    hep-phEPJC(2019)·5 citations
17. 17*

    Flows of multicomponent scalar models with U(1) gauge symmetry

    G. Fejos🇯🇵 · T. Hatsuda🇯🇵

    We investigate the renormalization group flows of multicomponent scalar theories with $U(1)$ gauge symmetry using the functional renormalization group method. The scalar sector is built up from traces of matrix fields that belong to simple, compact Lie algebras. We find that in general these theories are non-renormalizable even at zero gauge coupling, but if we add a $U(1)$ factor to the Lie algebra structure, then they are consistent. In accordance with our earlier findings, fluctuations introduce anomalous, regulator dependent gauge contributions, which are only consistent with the flow equation for a given set of gauge fixing parameters. We establish connections between regularization procedures in the standard covariant and the $R_{\xi }$ gauges arguing that one is not tied by introducing regulators at the level of the functional integral, and it is allowed to switch between schemes at different levels of the calculations. We calculate $\beta$ functions, classify fixed points, and clarify compatibility of the flow equation and the Ward-Takahashi identity between the scalar wavefunction renormalization and the charge rescaling factor.

    hep-phPRD(2019)·4 citations
18. 18*

    A First Determination of Parton Distributions with Theoretical Uncertainties

    The NNPDF Collaboration: Rabah Abdul Khalek🇳🇱 · Richard D. Ball🇬🇧 · Stefano Carrazza🇮🇹 · Stefano Forte🇮🇹 · Tommaso Giani🇬🇧 · Zahari Kassabov🇬🇧 · Emanuele R. Nocera🇳🇱 · Rosalyn L. Pearson🇬🇧 · Juan Rojo🇳🇱 · Luca Rottoli🇮🇹 · Maria Ubiali🇬🇧 · Cameron Voisey🇬🇧 · Michael Wilson🇬🇧

    The parton distribution functions (PDFs) which characterize the structure of the proton are currently one of the dominant sources of uncertainty in the predictions for most processes measured at the Large Hadron Collider (LHC). Here we present the first extraction of the proton PDFs that accounts for the missing higher order uncertainty (MHOU) in the fixed-order QCD calculations used in PDF determinations. We demonstrate that the MHOU can be included as a contribution to the covariance matrix used for the PDF fit, and then introduce prescriptions for the computation of this covariance matrix using scale variations. We validate our results at next-to-leading order (NLO) by comparison to the known next order (NNLO) corrections. We then construct variants of the NNPDF3.1 NLO PDF set that include the effect of the MHOU, and assess their impact on the central values and uncertainties of the resulting PDFs.

    hep-phhep-exnucl-thEPJC(2019)·97 citations
19. 19*

    Searching for Dark Photon Dark Matter in LIGO O1 Data

    Huai-Ke Guo🇺🇸 · Keith Riles🇺🇸 · Feng-Wei Yang🇨🇳 · Yue Zhao🇺🇸

    Dark matter exists in our Universe, but its nature remains mysterious. The remarkable sensitivity of the Laser Interferometer Gravitational-Wave Observatory (LIGO) may be able to solve this mystery. A good dark matter candidate is the ultralight dark photon. Because of its interaction with ordinary matter, it induces displacements on LIGO mirrors that can lead to an observable signal. In a study that bridges gravitational wave science and particle physics, we perform a direct dark matter search using data from LIGO's first (O1) data run, as opposed to an indirect search for dark matter via its production of gravitational waves. We demonstrate an achieved sensitivity on squared coupling as $\sim 4\times 10^{-45}$, in a $U(1{)}_{\mathrm{B}}$ dark photon dark matter mass band around $m_{\mathrm{A}}\sim 4\times 10^{-13}$eV. Substantially improved search sensitivity is expected during the coming years of continued data taking by LIGO and other gravitational wave detectors in a growing global network.

    hep-phastro-ph.COCommun.Phys.(2019)·88 citations
20. 20*

    Spin-Dependent Light Dark Matter Constraints from Mediators

    Harikrishnan Ramani🇺🇸 · Graham Woolley🇺🇸

    A bevy of light dark matter direct detection experiments have been proposed, targeting spin-independent dark matter scattering. In order to be exhaustive, non-standard signatures that have been investigated in the WIMP window including spin-dependent dark matter scattering also need to be looked into in the light dark matter parameter space. In this work, we promote this endeavor by deriving indirect limits on sub-GeV spin-dependent dark matter through terrestrial and astrophysical limits on the forces that mediate this scattering.

    hep-phastro-ph.CO7 citations
21. 21*

    Critical behavior and net-charge fluctuations from lattice QCD

    Frithjof Karsch🇩🇪

    We present recent results on the critical and pseudo-critical temperatures in (2+1)-flavor QCD with a physical strange quark mass and two degenerate light quark masses extrapolated to the chiral limit and tuned to the physical value, respectively. We furthermore discuss implication of the observed low chiral phase transition temperature, Tc0=132_{-6}^{+3} MeV, for the structure of cumulants of conserved charge fluctuations at vanishing baryon chemical potential and consequences for the possible location of the QCD critical endpoint in the QCD phase diagram at non-zero baryon chemical potential.

    ↳ hep-lathep-phPoS(2019)·48 citations
22. 22*

    Determination of the invisible energy of extensive air showers from the data collected at Pierre Auger Observatory

    Analisa G. Mariazzi (for the Pierre Auger Collaboration)🇦🇷

    In order to get the primary energy of cosmic rays from their extensive air showers using the fluorescence detection technique, the invisible energy should be added to the measured calorimetric energy. The invisible energy is the energy carried away by particles that do not deposit all their energy in the atmosphere. It has traditionally been calculated using Monte Carlo simulations that are dependent on the assumed primary particle mass and on model predictions for neutrino and muon production. In this work the invisible energy is obtained directly from events detected by the Pierre Auger Observatory. The method applied is based on the correlation of the measurements of the muon number at the ground with the invisible energy of the showers. By using it, the systematic uncertainties related to the unknown mass composition and to the high energy hadronic interaction models are significantly reduced, improving in this way the estimation of the energy scale of the Observatory.

    ↳ astro-ph.HEastro-ph.IMhep-exhep-phEPJ Web Conf.(2019)·1 citation
23. 23*

    Functional methods for false vacuum decay in real time

    Wen-Yuan Ai🇩🇪 · Bjorn Garbrecht🇩🇪 · Carlos Tamarit🇩🇪

    We present the calculation of the Feynman path integral in real time for tunneling in quantum mechanics and field theory, including the first quantum corrections. For this purpose, we use the well-known fact that Euclidean saddle points in terms of real fields can be analytically continued to complex saddles of the action in Minkowski space. We also use Picard-Lefschetz theory in order to determine the middle-dimensional steepest-descent surface in the complex field space, constructed from Lefschetz thimbles, on which the path integral is to be performed. As an alternative to extracting the decay rate from the imaginary part of the ground-state energy of the false vacuum, we use the optical theorem in order to derive it from the real-time amplitude for forward scattering. While this amplitude may in principle be obtained by analytic continuation of its Euclidean counterpart, we work out in detail how it can be computed to one-loop order at the level of the path integral, i.e. evaluating the Gaußian integrals of fluctuations about the relevant complex saddle points. To that effect, we show how the eigenvalues and eigenfunctions on a thimble can be obtained by analytic continuation of the Euclidean eigensystem, and we determine the path-integral measure on thimbles. This way, using real-time methods, we recover the one-loop result by Callan and Coleman for the decay rate. We finally demonstrate our real-time methods explicitly, including the construction of the eigensystem of the complex saddle, on the archetypical example of tunneling in a quasi-degenerate quartic potential.

    ↳ hep-thhep-phJHEP(2019)·78 citations
24. 24*

    UV Completion on the Worldline

    Steven Abel🇬🇧 · Nicola Andrea Dondi🇩🇰

    A framework for UV completing particle theories is proposed, based on the worldline formalism, which is equivalent to weighting all sums over histories with a proper-time dependent measure that has a smallest proper-time. We deduce a criterion to avoid ghosts, and find that the ghost-free theories have the (string-theory inspired) infinite-derivative model of Siegel as a special case, but represent a significant generalisation. Generically, the UV of such theories is dominated by a saddle-point in the proper-time, leading to simplification in the computation of amplitudes. We focus on a particularly attractive option which is to mimic the regulating properties of modular invariance with a worldline "inversion symmetry".

    ↳ hep-thgr-qchep-phJHEP(2019)·24 citations
25. 25*

    Square-Lattice Antiferromagnet Subjected to a Magnetic Field Aligned with the Order Parameter

    Christoph P. Hofmann🇲🇽

    The thermal properties of antiferromagnetic films -- in particular, the square-lattice antiferromagnet -- subjected to an external magnetic field pointing into the direction of the staggered magnetization are explored. The effective field theory analysis of the free energy density is carried out to two-loop order. While the emphasis is on finite temperature, we also discuss the behavior of the magnetization and staggered magnetization at zero temperature. Our results imply that the staggered magnetization increases in presence of the magnetic field -- reminiscent of magnetic catalysis. Most remarkably, if staggered and magnetic field strength are kept fixed, the magnetization initially grows when temperature increases.

    ↳ cond-mat.str-elhep-lathep-phJ.Stat.Mech.(2020)·2 citations
26. 26*

    Phases of Flavor Broken QCD${}_3$

    Andrew Baumgartner🇺🇸

    We map out the phase diagram of QCD${}_3$ with a product flavor group of the form $U(f)\times U(F)$. We find interesting structures emerge when $f+F>k$ depending on the relative sizes of $f$,$F$ and $k$. In particular, there exists phase transitions in which a Grassmannian phase will disappear and reappear in a different part of the phase diagram.

    ↳ hep-thcond-mat.str-elhep-phJHEP(2019)·8 citations
27. 27*

    BlackHawk v2.0: A public code for calculating the Hawking evaporation spectra of any black hole distribution

    Alexandre Arbey🇫🇷 · Jérémy Auffinger🇫🇷

    We describe BlackHawk, a public C program for calculating the Hawking evaporation spectra of any black hole distribution. This program allows the users to compute the primary and secondary spectra of stable or long-lived particles generated by Hawking radiation of the distribution of black holes, and to study their evolution in time. The physics of Hawking radiation is presented, and the capabilities, features and usage of BlackHawk are described here under the form of a manual. This is the BlackHawk v2.0 manual, which is available on the BlackHawk webpage http://blackhawk.hepforge.org/. A brief release note summarizing the new aspects of BlackHawk v2.0 as well as illustrating examples can be found in https://arxiv.org/abs/2108.02737.

    ↳ gr-qcastro-ph.COastro-ph.HEhep-phEPJC(2019)·227 citations
28. 28*

    Spectral Reconstruction with Deep Neural Networks

    Lukas Kades🇩🇪 · Jan M. Pawlowski🇩🇪 · Alexander Rothkopf🇳🇴 · Manuel Scherzer🇩🇪 · Julian M. Urban🇩🇪 · Sebastian J. Wetzel🇩🇪 · Nicolas Wink🇩🇪 · Felix P. G. Ziegler🇩🇪

    We explore artificial neural networks as a tool for the reconstruction of spectral functions from imaginary time Green's functions, a classic ill-conditioned inverse problem. Our ansatz is based on a supervised learning framework in which prior knowledge is encoded in the training data and the inverse transformation manifold is explicitly parametrised through a neural network. We systematically investigate this novel reconstruction approach, providing a detailed analysis of its performance on physically motivated mock data, and compare it to established methods of Bayesian inference. The reconstruction accuracy is found to be at least comparable, and potentially superior in particular at larger noise levels. We argue that the use of labelled training data in a supervised setting and the freedom in defining an optimisation objective are inherent advantages of the present approach and may lead to significant improvements over state-of-the-art methods in the future. Potential directions for further research are discussed in detail.

    ↳ physics.comp-phcs.LGhep-lathep-phPRD(2020)·84 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.