Wed·Sep 13, 2017Wednesday·September 13, 2017

1. 01*

   Approach to equilibrium of quarkonium in quark-gluon plasma

   Xiaojun Yao🇺🇸 · Berndt Müller🇺🇸

   We calculate the dissociation and recombination rates of ${\rm Y}(1S)$ in quark-gluon plasma by using potential non-relativistic QCD. We then study the dynamical in-medium evolution of the $b\bar{b}-{\rm Y}$ system in a periodic box via the Boltzmann equation and explore how the system reaches equilibrium. We find that interactions between the free heavy quarks and the medium are necessary for the system to reach equilibrium. We find that the angular distribution of ${\rm Y}(1S)$ probes the stages at which recombination occurs. Finally, we study the system under a longitudinal expansion and show that different initial conditions evolve to distinct final ratios of hidden and open $b$ flavors. We argue that experimental measurements of the ratio could address open questions in the quarkonium production in heavy ion collisions.

   hep-phhep-exnucl-exnucl-thPRC(2018)·65 citations
2. 02*

   An Elliptic Generalization of Multiple Polylogarithms

   Ettore Remiddi🇮🇹 · Lorenzo Tancredi🇩🇪

   We introduce a class of functions which constitutes an obvious elliptic generalization of multiple polylogarithms. A subset of these functions appears naturally in the \epsilon-expansion of the imaginary part of the two-loop massive sunrise graph. Building upon the well known properties of multiple polylogarithms, we associate a concept of weight to these functions and show that this weight can be lowered by the action of a suitable differential operator. We then show how properties and relations among these functions can be studied bottom-up starting from lower weights.

   hep-phhep-thNPB(2017)·123 citations
3. 03*

   Resolvable heavy neutrino-antineutrino oscillations at colliders

   Stefan Antusch🇨🇭 · Eros Cazzato🇨🇭 · Oliver Fischer🇩🇪

   Heavy neutrino-antineutrino oscillations can naturally appear in mechanisms of low scale neutrino mass generation, where pairs of heavy neutrinos have almost degenerate masses. We discuss the case where the heavy neutrinos are sufficiently long-lived to decay displaced from the primary vertex, such that the oscillations of the heavy neutrinos into antineutrinos can potentially be observed at the (high-luminosity) LHC and at currently planned future collider experiments. The observation of these oscillations would have far-reaching consequences: it would, for instance, prove the existence of lepton number violation and the Majorana nature of neutrino masses, and it would allow a deep insight into the nature of the neutrino mass generation mechanism.

   hep-phMod.Phys.Lett.A(2019)·89 citations
4. 04*

   Low scale supersymmetry at the LHC with jet and missing energy signature

   S.V. Demidov🇷🇺 · I.V. Sobolev🇩🇪

   If supersymmetry is broken at TeV scale, particles from sector responsible for supersymmetry breaking - goldstino and sgoldstinos - can reveal themselves already at the LHC experiments. We discuss bounds on supersymmetry breaking scale from the LHC searches for events with a jet plus missing momentum signature focusing on the case of TeV scale sgoldstinos. We show that contribution of light sgoldstinos to the cross section of of gravitino pair production with a jet can be sizable and the bounds on the gravitino mass can be stronger by up to a factor of 2 as compared to those obtained in the heavy sgoldstino limit. We compare these bounds on parameters of the model to those obtained with the results of ATLAS and CMS searches for dijet resonances.

   hep-ph3 citations
5. 05*

   The Gluon condensation in high energy cosmic rays

   Wei Zhu · Jiangshan Lan · Jianhong Ruan

   The gluon condensation (GC)-effects in high energy cosmic rays are investigated. After a brief review of the GC, several examples including gamma-, electron-, and positron-spectra in a broad GeV$\sim$TeV region can be explained by the GC-effects. We find that the GC may break the power-law of the cosmic ray spectra if the energy of accelerated protons exceeds the GC-threshold. The GC is a new phenomenon that is not yet known, it provides a new window to understand the high energy cosmic ray spectra.

   hep-phastro-ph.HEhep-exIJMPE(2018)·20 citations
6. 06*

   An empirical model of the long-distance contributions to ${\bar{B}}^0\to {\bar{K}}^{\ast 0}{\mu }^{+}{\mu }^{-}$ transitions

   Thomas Blake🇬🇧 · Ulrik Egede🇬🇧 · Patrick Owen🇨🇭 · Gabriela Pomery🇬🇧 · Konstantinos Alexandros Petridis🇬🇧

   A method for analysing the hadronic resonance contributions in ${\bar{B}}^0\to {\bar{K}}^{\ast 0}{\mu }^{+}{\mu }^{-}$ decays is presented. This method uses an empirical model that relies on measurements of the branching fractions and polarisation amplitudes of final states involving $J^{PC}=1^{--}$ resonances, relative to the short-distance component, across the full dimuon mass spectrum of ${\bar{B}}^0\to {\bar{K}}^{\ast 0}{\mu }^{+}{\mu }^{-}$ transitions. The model is in good agreement with existing calculations of hadronic non-local effects. The effect of this contribution to the angular observables is presented and it is demonstrated how the narrow resonances in the $q^2$ spectrum provide a dramatic enhancement to $CP$-violating effects in the short-distance amplitude. Finally, a study of the hadronic resonance effects on lepton universality ratios, $R_{K^{(\ast )}}$, in the presence of new physics is presented.

   hep-phhep-exEPJC(2018)·89 citations
7. 07*

   Ultraboosted $Zt$ and $\gamma t$ production at the HL-LHC and FCC-hh

   J. A. Aguilar-Saavedra🇪🇸

   Searches for anomalous $Zt$ and $\gamma t$ production provide an excellent probe of flavour-changing top interactions when the energies considered are very large. In this note we estimate the sensitivity to these interactions at the high luminosity phase of the LHC and a future 100 TeV $pp$ collider (FCC-hh). For the LHC, the expected limits on $t\to uZ/u\gamma$ branching ratios from $Zt$ and $\gamma t$ production will reach the $10^{-5}$ level, one order of magnitude better than the existing projections for $t\to uZ$ from $t\bar{t}$ production. For the FCC-hh, the limits on $t\to uZ/u\gamma$ could reach an impressive sensitivity at the $10^{-6}$ level, with limits on $t\to cZ/c\gamma$ at the $10^{-5}$ level.

   hep-phhep-exEPJC(2017)·12 citations
8. 08*

   New perspectives on constant-roll inflation

   F. Cicciarella🇮🇹 · J. Mabillard🇬🇧 · M. Pieroni🇪🇸

   We study constant-roll inflation using the $\beta$-function formalism. We show that the constant rate of the inflaton roll is translated into a first order differential equation for the $\beta$-function which can be solved easily. The solutions to this equation correspond to the usual constant-roll models. We then construct, by perturbing these exact solutions, more general classes of models that satisfy the constant-roll equation asymptotically. In the case of an asymptotic power law solution, these corrections naturally provide an end to the inflationary phase. Interestingly, while from a theoretical point of view (in particular in terms of the holographic interpretation) these models are intrinsically different from standard slow-roll inflation, they may have phenomenological predictions in good agreement with present cosmological data.

   ↳ astro-ph.COgr-qchep-phJCAP(2018)·59 citations
9. 09*

   Collective long-range particle correlations in proton-proton and proton-nucleus collisions at the LHC with the CMS detector

   Zhenyu Chen🇺🇸

   Measurements of two-particle angular correlations of inclusive charged particles as well as identified strange hadron in pp and pPb collisions are presented over a wide range in pseudorapidity and full azimuth. The data were collected using the CMS detector at the LHC, with nucleon-nucleon center-of-mass energy of 5.02 TeV for pPb collisions and 5, 7, 13 TeV for pp collisions. The results are compared to semi-peripheral PbPb collision data at center-of-mass energy of 2.76 TeV, covering similar charged-particle multiplicity ranges of the events. For high-multiplicity pp and pPb events, a clear particle species dependence of $v_2$ is observed for $p_T\lesssim 2$ GeV/c. When divided by the number of constituent quarks and compared at the same transverse kinetic energy per quark, a universal scaling over a broad range of particle transverse kinetic energy has been observed. For high-multiplicity pp collisions at 13 TeV, the $v_2$ values obtained for inclusive charged particles with two-, four- and six-particle correlations are found to be comparable within uncertainties. These measurements provide strong evidence for the collective nature of the long-range correlations observed in pp collisions.

   ↳ nucl-exhep-exhep-phnucl-th2 citations
10. 10*

    Photon emission from quark-gluon plasma out of equilibrium

    Sigtryggur Hauksson🇨🇦 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦

    The photon emission from a non-equilibrium quark-gluon plasma (QGP) is analyzed. We derive an integral equation that describes photon production through quark-antiquark annihilation and quark bremsstrahlung. It includes coherence between different scattering sites, also known as the Landau-Pomeranchuk-Migdal effect. These leading-order processes are studied for the first time together in an out-of-equilibrium field theoretical treatment that enables the inclusion of viscous corrections to the calculation of electromagnetic emission rates. In the special case of an isotropic, viscous, plasma the integral equation only depends on three constants which capture the non-equilibrium nature of the medium.

    ↳ nucl-thhep-phPRC(2018)·33 citations
11. 11*

    Status of the asymptotic safety paradigm for quantum gravity and matter

    Astrid Eichhorn🇩🇪

    In the asymptotic safety paradigm, a quantum field theory reaches a regime with quantum scale invariance in the ultraviolet, which is described by an interacting fixed point of the Renormalization Group. Compelling hints for the viability of asymptotic safety in quantum gravity exist, mainly obtained from applications of the functional Renormalization Group. The impact of asymptotically safe quantum fluctuations of gravity at and beyond the Planck scale could at the same time induce an ultraviolet completion for the Standard Model of particle physics with high predictive power.

    ↳ gr-qchep-phhep-thFound.Phys.(2018)·138 citations
12. 12*

    Tadpole diagrams in constant electromagnetic fields

    Felix Karbstein🇩🇪

    We show how all possible one-particle reducible tadpole diagrams in constant electromagnetic fields can be constructed from one-particle irreducible constant-field diagrams. The construction procedure is essentially algebraic and involves differentiations of the latter class of diagrams with respect to the field strength tensor and contractions with derivatives of the one-particle irreducible part of the Heisenberg-Euler effective Lagrangian in constant fields. Specific examples include the two-loop addendum to the Heisenberg-Euler effective action as well as a novel one-loop correction to the charged particle propagator in constant electromagnetic fields discovered recently. As an additional example, the approach devised in the present article is adopted to derive the tadpole contribution to the two-loop photon polarization tensor in constant fields for the first time.

    ↳ hep-thhep-phJHEP(2017)·22 citations
13. 13*

    Shear viscosity of a hadron gas and influence of resonance lifetimes on relaxation time

    J.-B. Rose🇩🇪 · J. M. Torres-Rincon🇩🇪 · A. Schäfer🇩🇪 · D. R. Oliinychenko🇩🇪 · H. Petersen🇩🇪

    We address a discrepancy between different computations of $\eta /s$ (shear viscosity over entropy density) of hadronic matter. Substantial deviations of this coefficient are found between transport approaches mainly based on resonance propagation with finite lifetime and other (semi-analytical) approaches with energy-dependent cross-sections, where interactions do not introduce a timescale. We provide an independent extraction of this coefficient by using the newly-developed SMASH (Simulating Many Accelerated Strongly interacting Hadrons) transport code, which is an example of a mainly resonance-based approach. We compare the results from SMASH with numerical solutions of the Boltzmann equation for simple systems using the Chapman-Enskog expansion, as well as previous results in the literature. Our conclusion is that the hadron interaction via resonance formation/decay strongly affects the transport properties of the system, resulting in significant differences in $\eta /s$ with respect to other approaches where binary collisions dominate. We argue that the relaxation time of the system ---which characterizes the shear viscosity--- is determined by the interplay between the mean-free time and the lifetime of resonances. We show how an artificial shortening of the resonance lifetimes, or the addition of a background elastic cross section nicely interpolate between the two discrepant results.

    ↳ nucl-thhep-phPRC(2018)·97 citations
14. 14*

    Stochastic gravitational waves from cosmic string loops in scaling

    Christophe Ringeval🇧🇪 · Teruaki Suyama🇯🇵

    If cosmic strings are formed in the early universe, their associated loops emit gravitational waves during the whole cosmic history and contribute to the stochastic gravitational wave background at all frequencies. We provide a new estimate of the stochastic gravitational wave spectrum by considering a realistic cosmological loop distribution, in scaling, as it can be inferred from Nambu-Goto numerical simulations. Our result takes into account various effects neglected so far. We include both gravitational wave emission and backreaction effects on the loop distribution and show that they produce two distinct features in the spectrum. Concerning the string microstructure, in addition to the presence of cusps and kinks, we show that gravitational wave bursts created by the collision of kinks could dominate the signal for wiggly strings, a situation which may be favoured in the light of recent numerical simulations. In view of these new results, we propose four prototypical scenarios, within the margin of the remaining theoretical uncertainties, for which we derive the corresponding signal and estimate the constraints on the string tension put by both the LIGO and European Pulsar Timing Array (EPTA) observations. The less constrained of these scenarios is shown to have a string tension GU < 7.2 x 10^{-11}, at 95% of confidence. Smooth loops carrying two cusps per oscillation verify the two-sigma bound GU < 1.0 x 10^{-11} while the most constrained of all scenarios describes very kinky loops and satisfies GU < 6.7 x 10^{-14} at 95% of confidence.

    ↳ astro-ph.COgr-qchep-phhep-thJCAP(2017)·132 citations
15. 15*

    Rydberg states of hydrogen-like ions in braneworld

    F. Dahia🇧🇷 · E. Maciel🇧🇷 · A. S. Lemos🇧🇷

    It has been argued that precise measurements of optical transition frequencies between Rydberg states of hydrogen-like ions could be used to obtain an improved value of the Rydberg constant and even to test Quantum Electrodynamics (QED) theory more accurately, by avoiding the uncertainties about the proton radius. Motivated by this perspective, we investigate the influence of the gravitational interaction on the energy levels of Hydrogen-like ions in Rydberg states within the context of the braneworld models. As it is known, in this scenario, the gravitational interaction is amplified in short distances. We show that, for Rydberg states, the main contribution for the gravitational potential energy does not come from the rest energy concentrated on the nucleus but from the energy of the electromagnetic field created by its electrical charge, which is spread in space. The reason is connected to the fact that, when the ion is in a Rydberg state with high angular momentum, the gravitational potential energy is not computable in zero-width brane approximation due to the gravitational influence of the electrovacuum in which the lepton is moving. Considering a thick brane scenario, we calculate the gravitational potential energy associated to the nucleus charge in terms of the confinement parameter of the electric field in the brane. We show that the gravitational effects on the energy levels of a Rydberg state can be amplified by the extra dimensions even when the compactification scale of the hidden dimensions is shorter than the Bohr radius.

    ↳ gr-qchep-phphysics.atom-phEPJC(2018)·8 citations
16. 16*

    Binary pulsars as probes of a Galactic dark matter disk

    Andrea Caputo🇨🇭 · Jesús Zavala🇮🇸 · Diego Blas🇨🇭

    As a binary pulsar moves through a wind of dark matter particles, the resulting dynamical friction modifies the binary's orbit. We study this effect for the double disk dark matter (DDDM) scenario, where a fraction of the dark matter is dissipative and settles into a thin disk. For binaries within the dark disk, this effect is enhanced due to the higher dark matter density and lower velocity dispersion of the dark disk, and due to its co-rotation with the baryonic disk.We estimate the effect and compare it with observations for two different limits in the Knudsen number ($Kn$). First, in the case where DDDM is effectively collisionless within the characteristic scale of the binary ($Kn\gg 1$) and ignoring the possible interaction between the pair of dark matter wakes. Second, in the fully collisional case ($Kn\ll 1$), where a fluid description can be adopted and the interaction of the pair of wakes is taken into account. We find that the change in the orbital period is of the same order of magnitude in both limits. A comparison with observations reveals good prospects to probe currently allowed DDDM models with timing data from binary pulsars in the near future. We finally comment on the possibility of extending the analysis to the intermediate (rarefied gas) case with $Kn\sim 1$.

    ↳ astro-ph.HEastro-ph.COhep-phPhys.Dark Univ.(2018)·22 citations
17. 17*

    Distillation of scalar exchange by coherent hypernucleus production in antiproton-nucleus collisions

    A.B. Larionov🇩🇪 · H. Lenske🇩🇪

    The total and angular differential cross sections of the coherent process $\bar{p}+{}^{A}Z\to {}_{\Lambda }^A(Z-1)+\bar{\Lambda }$ are evaluated at the beam momenta $1.5÷20$ GeV/c within the meson exchange model with bound proton and $\Lambda$-hyperon wave functions. It is shown that the shape of the beam momentum dependence of the hypernucleus production cross sections with various discrete $\Lambda$ states is strongly sensitive to the presence of the scalar $\kappa$-meson exchange in the $\bar{p}p\to \bar{\Lambda }\Lambda$ amplitude. This can be used as a clean test of the exchange by scalar $\pi K$ correlation in coherent $\bar{p}A$ reactions.

    ↳ nucl-thhep-exhep-phnucl-exPLB(2017)·6 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.