Mon·Sep 4, 2017Monday·September 4, 2017

1. 01*

   Timelike-helicity $B\to \pi \pi$ form factor from light-cone sum rules with dipion distribution amplitudes

   Shan Cheng🇩🇪 · Alexander Khodjamirian🇩🇪 · Javier Virto🇩🇪

   We complete the set of QCD light-cone sum rules for $B\to \pi \pi$ transition form factors, deriving a new sum rule for the timelike-helicity form factor $F_t$ in terms of dipion distribution amplitudes. This sum rule, in the leading twist-2 approximation, is directly related to the pion vector form factor. Employing a relation between $F_t$ and other $B\to \pi \pi$ form factors we obtain also the longitudinal-helicity form factor $F_0$. In this way, all four (axial-)vector $B\to \pi \pi$ form factors are predicted from light-cone sum rules with dipion distribution amplitudes. These results are valid for small dipion masses with large momentum.

   hep-phPRD(2017)·40 citations
2. 02*

   Photon-Photon Collisions with SuperChic

   L. A. Harland-Lang🇬🇧 · V. A. Khoze🇬🇧 · M. G. Ryskin🇷🇺

   The SuperChic Monte Carlo generator provides a common platform for QCD-mediated, photoproduction and photon-induced Central Exclusive Production (CEP), with a fully differential treatment of soft survival effects. In these proceedings we summarise the processes generated, before discussing in more detail those due to photon-photon collisions, paying special attention to the correct treatment of the survival factor. We briefly consider the light-by-light scattering process as an example, before discussing planned extensions and refinements for the generator.

   hep-phhep-exCERN Proc.(2018)·5 citations
3. 03*

   Particle temperature and the Chiral Vortical Effect in the early universe

   Tamal K. Mukherjee🇮🇳 · Soma Sanyal🇮🇳

   We study the effect of hotter or colder particles on the evolution of the chiral magnetic field in the early universe. We are interested in the temperature dependent term in the chiral vortical effect. There are no changes in the magnetic energy spectrum at large lengthscales but in the Kolmogorov regime we do find a difference. Our numerical results show that the Gaussian peak in the magnetic spectrum becomes negatively skewed. The negatively skewed peak can be fitted with a beta distribution. Analytically one can relate the non-Gaussianity of the distribution to the temperature dependent vorticity term. The vorticity term is therefore responsible for the beta distribution in the magnetic spectrum. Since the beta distribution has already been used to model turbulent dispersion in fluids, hence it seems that the presence of hotter or colder particles may lead to turbulence in the magnetized plasma.

   hep-phastro-ph.COMod.Phys.Lett.A(2017)·4 citations
4. 04*

   Particle yields from numerical simulations

   Marietta M. Homor🇭🇺 · Antal Jakovác🇭🇺

   In this paper we use numerical simulations to calculate the particle yields. We demonstrate that in the model of local particle creation the deviation from the pure exponential distribution is natural even in equilibrium, and an approximate Tsallis-Pareto-like distribution function can be well fitted to the calculated yields, in accordance with the experimental observations. We present numerical simulations in classical ${\Phi }^4$ model as well as in the SU(3) quantum Yang-Mills theory to clarify this issue.

   hep-phcond-mat.stat-mechhep-latPRD(2018)·2 citations
5. 05*

   Center phase transition from matter propagators in (scalar) QCD

   M. Mitter🇦🇹 · M. Hopfer🇦🇹 · B.-J. Schaefer🇩🇪 · R. Alkofer🇦🇹

   Novel order parameters for the confinement-deconfinement phase transition of quenched QCD and fundamentally charged scalar QCD are presented. Similar to the well-known dual condensate, they are defined via generalized matter propagators with $U(1)$-valued boundary conditions. The order parameters are easily accessible with functional methods. Their validity and accessibility is explicitly demonstrated by numerical studies of the Dyson-Schwinger equations for the matter propagators. Even in the case of heavy scalar matter, where the propagator does not show a signature of the phase transition, a discontinuity due to the transition can be extracted in the order parameters, establishing also fundamentally charged scalar matter as a probe for color confinement.

   hep-phhep-thnucl-thPLB(2018)·5 citations
6. 06*

   Implementing consistent NLO factorization in single inclusive forward hadron production

   B. Ducloué🇫🇮 · T. Lappi🇫🇮 · Y. Zhu🇫🇮

   Single inclusive forward hadron production in high-energy hadron collisions can provide an important test of the Color Glass Condensate picture at small $x$. Recent studies of this process at next-to-leading order have led to problematic results, with cross sections becoming negative at large transverse momenta. We study a new formulation of this quantity proposed recently by Iancu et al. We show that it leads to physical results up to large transverse momenta at fixed coupling. Taking into account running coupling effects in a way that is consistent with existing DIS calculations still poses a challenge.

   hep-phPoS(2018)·0 citations
7. 07*

   Update on extraction of transversity PDF from inclusive di-hadron production

   Marco Radici🇮🇹

   The transversity was recently extracted from data on the production of hadron pairs in semi-inclusive deep-inelastic scattering. This analysis can be conveniently performed in the framework of collinear factorization where the elementary mechanism is represented by the simple product of transversity and of a suitable chiral-odd function describing the fragmentation of a transversely polarized parton into a pair of hadrons inside the same current jet. The same elementary mechanism was predicted long ago to generate an asymmetry in the azimuthal distribution of the hadron pairs when they are produced in proton-proton collisions with one transversely polarized proton. Recently, the STAR Collaboration has observed this asymmetry. We analyze the impact of these data on our knowledge of transversity and we present its first preliminary extraction from a global fit of all data in hard processes with inclusive di-hadron production.

   hep-phhep-exnucl-exnucl-thPoS(2018)·0 citations
8. 08*

   The Large-$n_f$ Limit of the Four-Loop Splitting Functions in QCD

   Joshua Davies🇩🇪

   These proceedings describe a computation of the large-$n_f$ terms contributing to the QCD splitting functions at the fourth order in the strong coupling constant ${\alpha }_s$. Using the FORCER package for the reduction of four-loop two-point Feynman integrals, Mellin moments of the four-loop splitting functions have been computed. These moments are used to derive analytic Mellin-space expressions, by forming and finding solutions to systems of Diophantine equations. Expressions for the terms proportional to $n_f^3$ of the flavour singlet, and to $n_f^2$ of the flavour non-singlet splitting functions have been determined.

   hep-phPoS(2018)·1 citation
9. 09*

   Neutrino masses, leptogenesis and dark matter from small lepton number violation?

   Asmaa Abada🇫🇷 · Giorgio Arcadi🇩🇪 · Valerie Domcke🇩🇪 · Michele Lucente🇧🇪

   We consider the possibility of simultaneously addressing the baryon asymmetry of the Universe, the dark matter problem and the neutrino mass generation in minimal extensions of the Standard Model via sterile fermions with (small) total lepton number violation. Within the framework of Inverse and Linear Seesaw models, the small lepton number violating parameters set the mass scale of the active neutrinos, the efficiency of leptogenesis through a small mass splitting between pairs of sterile fermions as well as the mass scale of a sterile neutrino dark matter candidate. We provide an improved parametrization of these seesaw models taking into account existing experimental constraints and derive a linearized system of Boltzmann equations to describe the leptogenesis process, which allows for an efficient investigation of the parameter space. This in particular enables us to perform a systematic study of the strong washout regime of leptogenesis. Our study reveals that one can have a successful leptogenesis at the temperature of the electroweak scale through oscillations between two sterile states with a natural origin of the (necessary) strong degeneracy in their mass spectrum. The minimal model however requires a non-standard cosmological history to account for the relic dark matter. Finally, we discuss the prospect for neutrinoless double beta decay and for testing, in future experiments, the values of mass and different active-sterile mixings required for successful leptogenesis.

   hep-phastro-ph.COJCAP(2017)·68 citations
10. 10*

    Searches for new physics in lepton plus jet final states in ATLAS and CMS

    Francesco Romeo (on behalf of the ATLAS and CMS Collaboration)🇺🇸

    The most recent results on searches in lepton plus jet final states motivated by different models beyond the standard model are presented, using pp collision data collected by the ATLAS and CMS detectors during Run I and Run II at the CERN LHC. Leptoquarks and heavy Majorana neutrinos that arise in the left-right model are looked for in the final states with two leptons and two jets (ll + jj; l = e; mu; tau ). Heavy Majorana neutrinos are further investigated by relying on a composite-fermion scenario, considering two leptons and one large-radius jet (ll + J; l = e, mu), and in the context of a model with Type-1 seesaw mechanism, requiring two same-sign leptons plus dijet (ll' + jj; l,l' = e, mu). Finally, models of microscopic black holes with two to six extra dimensions are tested by analysing the channels with at least one lepton and two additional jets (l + jj; l = e, mu). In all the searches, the observed data are in good agreement with the standard model prediction and 95% confidence level upper limits are set on the parameters of difierent models.

    ↳ hep-exhep-ph3 citations
11. 11*

    Constraints through decaying inflaton: maximum reheating temperature

    Debaprasad Maity🇮🇳

    In this paper we study the reheating constraints on inflationary models considering perturbatively decaying inflaton. Important difference with the existing analysis is the inclusion of explicit decaying dynamics of inflaton during reheating. One of the important findings of our analysis is the possible existence of maximum reheating temperature $T_{re}^{max}$ considering perturbative reheating scenario. For all the models under consideration the value of this temperature turned out to be $T_{re}^{max}\sim 10^{15}$ GeV. Corresponding to this value of reheating temperature the duration of reheating period assumes naturally small value, $N_{re}\simeq 0.3$ which indicates instantaneous reheating. Most importantly, maximum reheating temperature $T_{re}^{max}$ also leads to a maximum values of scalar spectral index $n_s^{max}$ and inflationary e-folding number $N_{cmb}^{max}$ in association with the observed CMB scale. Based on our general analysis, we have studied four different inflationary models, and discuss their predictions and constraints.

    ↳ hep-thhep-ph7 citations
12. 12*

    Giant collimated gamma-ray flashes

    Alberto Benedetti🇩🇪 · Matteo Tamburini🇩🇪 · Christoph H. Keitel🇩🇪

    Bright sources of high energy electromagnetic radiation are widely employed in fundamental research as well as in industry and medicine. This steadily growing interest motivated the construction of several facilities aiming at the realisation of sources of intense X- and gamma-ray pulses. To date, free electron lasers and synchrotrons provide intense sources of photons with energies up to 10-100 keV. Facilities under construction based on incoherent Compton back scattering of an optical laser pulse off an electron beam are expected to yield photon beams with energy up to 19.5 MeV and peak brilliance in the range 10${}^{20}$-10${}^{23}$ photons s${}^{-1}$ mrad${}^{-2}$ mm${}^{-2}$ per 0.1% bandwidth. Here, we demonstrate a novel mechanism based on the strongly amplified synchrotron emission which occurs when a sufficiently dense electron beam interacts with a millimetre thickness solid target. For electron beam densities exceeding approximately 3\times10^{19}\text{ cm^{-3}} filamentation instability occurs with the self-generation of 10${}^7$-10${}^8$ gauss magnetic fields where the electrons of the beam are trapped. This results into a giant amplification of synchrotron emission with the production of collimated gamma-ray pulses with peak brilliance above $10^{25}$ photons s${}^{-1}$ mrad${}^{-2}$ mm${}^{-2}$ per 0.1% bandwidth and photon energies ranging from 200 keV up to several hundreds MeV. These findings pave the way to compact, high-repetition-rate (kHz) sources of short (30 fs), collimated (mrad) and high flux ($>10^{12}$ photons/s) gamma-ray pulses.

    ↳ physics.plasm-phastro-ph.HEhep-phNature Photon.(2018)·39 citations
13. 13*

    Systematic errors in transport calculations of shear viscosity using the Green-Kubo formalism

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

    The purpose of this study is to provide a reproducible framework in the use of the Green-Kubo formalism to extract transport coefficients. More specifically, in the case of shear viscosity, we investigate the limitations and technical details of fitting the auto-correlation function to a decaying exponential. This fitting procedure is found to be applicable for systems interacting both through constant and energy-dependent cross-sections, although this is only true for sufficiently dilute systems in the latter case. We find that the optimal fit technique consists in simultaneously fixing the intercept of the correlation function and use a fitting interval constrained by the relative error on the correlation function. The formalism is then applied to the full hadron gas, for which we obtain the shear viscosity to entropy ratio.

    ↳ nucl-thhep-phJ.Phys.Conf.Ser.(2018)·6 citations
14. 14*

    First lattice QCD study of the gluonic structure of light nuclei

    Frank Winter🇺🇸 · William Detmold🇺🇸 · Arjun S. Gambhir🇺🇸 · Kostas Orginos🇺🇸 · Martin J. Savage🇺🇸 · Phiala E. Shanahan🇺🇸 · Michael L. Wagman🇺🇸

    The role of gluons in the structure of the nucleon and light nuclei is investigated using lattice quantum chromodynamics (QCD) calculations. The first moment of the unpolarised gluon distribution is studied in nuclei up to atomic number $A=3$ at quark masses corresponding to pion masses of $m_{\pi }\sim 450$ and $806$ MeV. Nuclear modification of this quantity defines a gluonic analogue of the EMC effect and is constrained to be less than $\sim 10$% in these nuclei. This is consistent with expectations from phenomenological quark distributions and the momentum sum rule. In the deuteron, the combination of gluon distributions corresponding to the $b_1$ structure function is found to have a small first moment compared with the corresponding momentum fraction. The first moment of the gluon transversity structure function is also investigated in the spin-1 deuteron, where a non-zero signal is observed at $m_{\pi }\sim 806$ MeV. This is the first indication of gluon contributions to nuclear structure that can not be associated with an individual nucleon.

    ↳ hep-lathep-phPRD(2017)·55 citations
15. 15*

    Higgs-curvature coupling and post-inflationary vacuum instability

    Daniel G. Figueroa🇨🇭 · Arttu Rajantie🇬🇧 · Francisco Torrenti🇪🇸

    We study the post-inflationary dynamics of the Standard Model (SM) Higgs field in the presence of a non-minimal coupling $\xi |\Phi {|}^{2}R$ to gravity, both with and without the electroweak gauge fields coupled to the Higgs. We assume a minimal scenario in which inflation and reheating are caused by chaotic inflation with a quadratic potential, and no additional new physics is relevant below the Planck scale. By using classical real-time lattice simulations with a renormalisation group improved effective Higgs potential and by demanding the stability of the Higgs vacuum after inflation, we obtain upper bounds for $\xi$, taking into account the experimental uncertainty of the top-Yukawa coupling. We compare the bounds in the absence and presence of the electroweak gauge bosons, and conclude that the addition of gauge interactions has a rather minimal impact. In the unstable cases, we parametrize the time when such instability develops. For a top-quark mass $m_t\approx 173.3\mathrm{GeV}$, the Higgs vacuum instability is triggered for $\xi \gtrsim 4-5$, although a slightly lower mass of $m_t\approx 172.1\mathrm{GeV}$ pushes up this limit to $\xi \gtrsim 11-12$. This, together with the estimation $\xi \gtrsim 0.06$ for stability during inflation, provides tight constraints to the Higgs-curvature coupling within the SM.

    ↳ astro-ph.COhep-phPRD(2018)·57 citations
16. 16*

    Mapping Extragalactic Dark Matter Annihilation with Galaxy Surveys: A Systematic Study of Stacked Group Searches

    Mariangela Lisanti🇺🇸 · Siddharth Mishra-Sharma🇺🇸 · Nicholas L. Rodd🇺🇸 · Benjamin R. Safdi🇺🇸 · Risa H. Wechsler🇺🇸

    Dark matter in the halos surrounding galaxy groups and clusters can annihilate to high-energy photons. Recent advancements in the construction of galaxy group catalogs provide many thousands of potential extragalactic targets for dark matter. In this paper, we outline a procedure to infer the dark matter signal associated with a given galaxy group. Applying this procedure to a catalog of sources, one can create a full-sky map of the brightest extragalactic dark matter targets in the nearby Universe ($z\lesssim 0.03$), supplementing sources of dark matter annihilation from within the Local Group. As with searches for dark matter in dwarf galaxies, these extragalactic targets can be stacked together to enhance the signals associated with dark matter. We validate this procedure on mock $\text{Fermi}$ gamma-ray data sets using a galaxy catalog constructed from the $\text{DarkSky}$ $N$-body cosmological simulation and demonstrate that the limits are robust, at $\mathcal{O}(1)$ levels, to systematic uncertainties on halo mass and concentration. We also quantify other sources of systematic uncertainty arising from the analysis and modeling assumptions. Our results suggest that a stacking analysis using galaxy group catalogs provides a powerful opportunity to discover extragalactic dark matter and complements existing studies of Milky Way dwarf galaxies.

    ↳ astro-ph.COastro-ph.HEhep-phPRD(2018)·60 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.