Fri·Feb 9, 2018Friday·February 9, 2018

1. 01*

   Dirac and Majorana Feynman Rules with four-fermions

   Michael Paraskevas🇬🇷

   A compact method for amplitude calculations in theories with Dirac and Majorana effective operators is discussed. Using the renormalizable formalism of Denner et al., [1,2] for propagators, vertices and fermion (number) flow and introducing new "reading-rules", it is shown that fermions can be treated as scalars in the diagrams. The effect of Fermi-statistics appears only in overall signs and is determined once for whole classes of diagrams. Each vertex in this method corresponds to two or more vertices in the standard treatment of effective theories. As such, the advantages of this approach grow together with the number of four-fermion vertices in a given diagram. The discussion develops around effective field theories based on the Standard Model, up to four-fermions and to any order in perturbation theory. Even so, the framework is more general and can be applied elsewhere.

   hep-phhep-th13 citations
2. 02*

   On the small-$x$ behavior of the orbital angular momentum distributions in QCD

   Yoshitaka Hatta🇯🇵 · Dong-Jing Yang🇹🇼

   We present the numerical solution of the leading order QCD evolution equation for the orbital angular momentum distributions of quarks and gluons and discuss its implications for the nucleon spin sum rule. We observe that at small-$x$, the gluon helicity and orbital angular momentum distributions are roughly of the same magnitude but with opposite signs, indicating a significant cancellation between them. A similar cancellation occurs also in the quark sector. We explain analytically the reason for this cancellation.

   hep-phPLB(2018)·19 citations
3. 03*

   A fast C++ implementation of thermal functions

   Andrew Fowlie🇦🇺

   We provide a small C++ library with Mathematica and Python interfaces for computing thermal functions, defined $$J_{\text{B/F}}(y^2)\equiv \Re {\int }_0^{\infty }{x}^2\log \left[1\mp e^{-\sqrt{x^2+y^2}}\right]\text{d}x,$$ which appear in finite-temperature quantum field theory and play a role in phase-transitions in the early Universe, including baryogenesis, electroweak symmetry breaking and the Higgs mechanism.

   hep-phphysics.comp-phComput.Phys.Commun.(2018)·21 citations
4. 04*

   Transverse momentum distributions of electron in simulated QED model

   Navdeep Kaur🇮🇳 · Harleen Dahiya🇮🇳

   In the present work, we have studied the transverse momentum distributions (TMDs) for the electron in simulated QED model. We have used the overlap representation of light-front wave functions (LFWFs) where the spin-1/2 relativistic composite system consists of spin-1/2 fermion and spin-1 vector boson. The results have been obtained for T-even TMDs in transverse momentum plane for fixed value of longitudinal momentum fraction $x$.

   hep-phFew Body Syst.(2018)·0 citations
5. 05*

   The photon polarization in radiative $D$ decays, phenomenologically

   Stefan de Boer🇩🇪 · Gudrun Hiller🇩🇪

   We work out the phenomenology of untagged time-dependent analysis with radiative $D^0$-decays into CP eigenstates, which allows to probe the photon polarization by means of the charm mesons' finite width difference. We show that $D^0\to \varphi \gamma$ or $D^0\to {\bar{K}}^{0\ast }\gamma$ decays, which are SM-dominated, or SM-like, respectively, together with U-spin allow to obtain chirality-predictions for radiative decay amplitudes. The order of magnitude of wrong-chirality contributions in the SM can be cross-checked with an up-down asymmetry in $D^0\to {\bar{K}}_1^0(\to \bar{K}\pi \pi )\gamma$. We explore the sensitivity to new physics in $|\Delta c|=|\Delta u|=1$ dipole couplings in the decays $D^0\to {\rho }^0\gamma$. We point out the possibility to test the SM with $D_s\to K_1^{+}(\to K\pi \pi )\gamma$ decays.

   hep-phhep-exEPJC(2018)·25 citations
6. 06*

   Constraining P and CP violation in the main decay of the neutral Sigma hyperon

   Shankar Sunil Nair🇸🇪 · Elisabetta Perotti🇸🇪 · Stefan Leupold (UU)🇸🇪

   On general grounds based on quantum field theory the decay amplitude for ${\Sigma }^0\to \Lambda \gamma$ consists of a parity conserving magnetic and a parity violating electric dipole transition moment. Because of the subsequent self-analyzing weak decay of the $\Lambda$ hyperon the interference between magnetic and electric dipole transition moment leads to an asymmetry in the angular distribution. Comparing the decay distributions for the ${\Sigma }^0$ hyperon and its antiparticle gives access to possible C and CP violation. Based on flavor SU(3) symmetry the present upper limit on the neutron electric dipole moment can be translated to an upper limit for the angular asymmetry. It turns out to be far below any experimental resolution that one can expect in the foreseeable future. Thus any true observation of a CP violating angular asymmetry would constitute physics beyond the standard model, even if extended by a CP violating QCD theta-vacuum-angle term.

   hep-phPLB(2019)·14 citations
7. 07*

   Real part of $pp$ scattering amplitude in Additive Quark Model at LHC energies

   Yu.M. Shabelski🇷🇺 · A.G. Shuvaev🇷🇺

   Elastic $pp$ scattering at LHC energies is treated in Additive Quark Model together with Pomeron exchange theory. The obtained results are compared with the new experimental data on the ratio of real to imaginary part of the scattering amplitude at the small transverse momenta

   hep-phEPJC(2018)·23 citations
8. 08*

   Gauge Invariant Noether's Theorem and The Proton Spin Crisis

   Gouranga C Nayak🇺🇸

   Due to proton spin crisis it is necessary to understand the gauge invariant definition of the spin and orbital angular momentum of the quark and gluon from first principle. In this paper we derive the gauge invariant Noether's theorem by using combined Lorentz transformation plus local gauge transformation. We find that the notion of the gauge invariant definition of the spin (or orbital) angular momentum of the electromagnetic field does not exist in Dirac-Maxwell theory although the notion of the gauge invariant definition of the spin (or orbital) angular momentum of the electron exists. We find that the gauge invariant definition of the spin angular momentum of the electromagnetic field in the literature is not correct because of the non-vanishing surface term in Dirac-Maxwell theory although the corresponding surface term vanishes for linear momentum. We also show that the Belinfante-Rosenfeld tensor is not required to obtain symmetric and gauge invariant energy momentum tensor of the electron and the electromagnetic field in Dirac-Maxwell theory.

   hep-phnucl-thJHEP(2018)·7 citations
9. 09*

   New Physics Phenomena and F-theory GUTs

   George K. Leontaris🇬🇷

   In this presentation the new physics implications of the $B$-meson decay anomalies, observed at LHCb, are discussed. In the first part of the talk a brief overview of the experimental status is presented. In the second part, a class of semi-local F-theory GUT models with additional neutral gauge bosons are proposed which are capable of accounting for the anomalous $B$-decay ratios $R_K$ and $R_{K^{\ast }}$

   hep-phhep-exhep-thPoS(2018)·0 citations
10. 10*

    Gravitational waves from first order electroweak phase transition in models with the $U(1{)}_X^{}$ gauge symmetry

    Katsuya Hashino🇯🇵 · Mitsuru Kakizaki🇯🇵 · Shinya Kanemura🇯🇵 · Pyungwon Ko🇰🇷 · Toshinori Matsui🇰🇷

    We consider a standard model extension equipped with a dark sector where the $U(1{)}_X^{}$ Abelian gauge symmetry is spontaneously broken by the dark Higgs mechanism. In this framework, we investigate patterns of the electroweak phase transition as well as those of the dark phase transition, and examine detectability of gravitational waves (GWs) generated by such strongly first order phase transition. It is pointed out that the collider bounds on the properties of the discovered Higgs boson exclude a part of parameter space that could otherwise generate detectable GWs. After imposing various constraints on this model, it is shown that GWs produced by multi-step phase transitions are detectable at future space-based interferometers, such as LISA and DECIGO, if the dark photon is heavier than 25 GeV. Furthermore, we discuss the complementarity of dark photon searches or dark matter searches with the GW observations in these models with the dark gauge symmetry.

    hep-phJHEP(2018)·88 citations
11. 11*

    Fragmentation-fraction ratio $f_{{\Xi }_b}/f_{{\Lambda }_b}$ in $b$- and $c$-baryon decays

    Hua-Yu Jiang🇨🇳 · Fu-Sheng Yu🇨🇳

    We study the ratio of fragmentation fractions, $f_{{\Xi }_b}/f_{{\Lambda }_b}$, from the measurement of ${\Xi }_b^0\to {\Xi }_c^{+}{\pi }^{-}$ and ${\Lambda }_b^0\to {\Lambda }_c^{+}{\pi }^{-}$ with ${\Xi }_c^{+}/{\Lambda }_c^{+}\to p{K}^{-}{\pi }^{+}$. With the branching fraction $\mathcal{B}({\Xi }_c^{+}\to p{K}^{-}{\pi }^{+})=(2.2\pm 0.8)\%$ obtained under the U-spin symmetry, the fragmentation ratio is determined as $f_{{\Xi }_b}/f_{{\Lambda }_b}$=$0.054\pm 0.020$. To reduce the above uncertainties, we suggest to measure the branching fractions of ${\Xi }_c^{+}\to p{\overline{K}}^{\ast 0}$ and ${\Lambda }_c^{+}\to {\Sigma }^{+}{K}^{\ast 0}$ at BESIII, Belle(II) and LHCb.

    hep-phhep-exEPJC(2018)·26 citations
12. 12*

    A new mechanism of sterile neutrino dark matter production

    Johannes Herms🇩🇪 · Alejandro Ibarra🇩🇪 · Takashi Toma🇩🇪

    We consider a scenario where the dark matter candidate is a sterile neutrino with sizable self-interactions, described by a dimension-six operator, and with negligible interactions with the Standard Model. The relic abundance is set by the freeze-out of 4-to-2 annihilations in the dark sector plasma and reproduces the observed dark matter abundance when the sterile neutrino mass is in the range $\sim 500\mathrm{keV}-20\mathrm{GeV}$. The feeble interactions with the Standard Model may lead to observable signals from dark matter decay. Furthermore, the self-interactions can affect the formation of small scale structures. We also implement this mechanism in a concrete model where the sterile neutrino self-interaction is due to the exchange of a singlet scalar, and we discuss the relevance of the scalar portal interactions for constructing a complete thermal history of the dark sector.

    hep-phJCAP(2018)·26 citations
13. 13*

    Soft Gluon Resummation in Higgs Boson Plus Two Jet Production at the LHC

    Peng Sun🇨🇳 · C.-P. Yuan🇺🇸 · Feng Yuan🇺🇸

    In this paper, the soft gluon resummation effect in the Higgs boson plus two-jet production at the LHC is studied. By applying the transverse momentum dependent factorization formalism, the large logarithms introduced by the small total transverse momentum of the Higgs boson plus two-jet final state system, are resummed to all orders in the expansion of the strong interaction coupling at the accuracy of Next-to-Leading Logarithm. We also compare our result with the prediction of the Monte Carlo event generator Pythia8, and found noticeable difference in the distributions of the total transverse momentum and the azimuthal angle correlations of the final state Higgs boson and two-jet system.

    hep-phPLB(2019)·5 citations
14. 14*

    NLO Higgs+jet at large transverse momenta including top quark mass effects

    Tobias Neumann🇺🇸

    We present a next-to-leading order calculation of H+jet in gluon fusion including the effect of a finite top quark mass $m_t$ at large transverse momenta. Using the recently published two-loop amplitudes in the high energy expansion and our previous setup that includes finite $m_t$ effects in a low energy expansion, we are able to obtain $m_t$-finite results for transverse momenta below 225 GeV and above 500 GeV with negligible remaining top quark mass uncertainty. The only remaining region that has to rely on the common leading order rescaling approach is the threshold region $\sqrt{\hat{s}}\simeq 2m_t$. We demonstrate that this rescaling provides an excellent approximation in the high $p_T$ region. Our calculation settles the issue of top quark mass effects at large transverse momenta. It is implemented in the parton level Monte Carlo code MCFM and is publicly available immediately in version 8.2.

    hep-phJ.Phys.Comm.(2018)·61 citations
15. 15*

    The muon $g-2$ and $\alpha (M_Z^2)$: a new data-based analysis

    Alexander Keshavarzi🇬🇧 · Daisuke Nomura🇯🇵 · Thomas Teubner🇬🇧

    This work presents a complete re-evaluation of the hadronic vacuum polarisation contributions to the anomalous magnetic moment of the muon, $a_{\mu }^{\mathrm{had},\mathrm{VP}}$ and the hadronic contributions to the effective QED coupling at the mass of the $Z$ boson, $\Delta {\alpha }_{\mathrm{had}}(M_Z^2)$, from the combination of $e^{+}{e}^{-}\to \mathrm{hadrons}$ cross section data. Focus has been placed on the development of a new data combination method, which fully incorporates all correlated statistical and systematic uncertainties in a bias free approach. All available $e^{+}{e}^{-}\to \mathrm{hadrons}$ cross section data have been analysed and included, where the new data compilation has yielded the full hadronic $R$-ratio and its covariance matrix in the energy range $m_{\pi }\le \sqrt{s}\le 11.2$ GeV. Using these combined data and pQCD above that range results in estimates of the hadronic vacuum polarisation contributions to $g-2$ of the muon of $a_{\mu }^{\mathrm{had},\mathrm{LO}\mathrm{VP}}=(693.27\pm 2.46)\times 10^{-10}$ and $a_{\mu }^{\mathrm{had},\mathrm{NLO}\mathrm{VP}}=(-9.82\pm 0.04)\times 10^{-10}$. The new estimate for the Standard Model prediction is found to be $a_{\mu }^{\mathrm{SM}}=(11659182.05\pm 3.56)\times 10^{-10}$, which is $3.7\sigma$ below the current experimental measurement. The prediction for the five-flavour hadronic contribution to the QED coupling at the $Z$ boson mass is $\Delta {\alpha }_{\mathrm{had}}^{(5)}(M_Z^2)=(276.11\pm 1.11)\times 10^{-4}$, resulting in ${\alpha }^{-1}(M_Z^2)=128.946\pm 0.015$. Detailed comparisons with results from similar related works are given.

    hep-phPRD(2018)·874 citations
16. 16*

    CP violating phases and a solution to the strong CP problem

    Renata Jora🇷🇴

    We present a solution to the strong CP problem based on the identification of the theta angle with twice the CP violating phase present in the CKM quark matrix. This solution washes out all the unwanted issues stemming form the strong CP phase and is strongly justified by general theoretical arguments based on the partition function associated to the $\theta$ vacuum. Phenomenological consequences on the quark mass matrices are discussed for this case.

    hep-ph0 citations
17. 17*

    Collider Tests of the Renormalizable Coloron Model

    Yang Bai🇺🇸 · Bogdan A. Dobrescu🇺🇸

    The coloron, a massive version of the gluon present in gauge extensions of QCD, has been searched for at the LHC as a dijet or top quark pair resonance. We point out that in the Renormalizable Coloron Model (ReCoM) with a minimal field content to break the gauge symmetry, a color-octet scalar and a singlet scalar are naturally lighter than the coloron because they are pseudo Nambu-Goldstone bosons. Consequently, the coloron may predominantly decay into scalar pairs, leading to novel signatures at the LHC. When the color-octet scalar is lighter than the singlet, or when the singlet mass is above roughly 1 TeV, the signatures consist of multi-jet resonances of multiplicity up to 12, including topologies with multi-prong jet substructure, slightly displaced vertices, and sometimes a top quark pair. When the singlet is the lightest ReCoM boson and lighter than about 1 TeV, its main decays ($W^{+}{W}^{-}$, $\gamma Z$, $ZZ$) arise at three loops. The LHC signatures then involve two or four boosted electroweak bosons, often originating from highly displaced vertices, plus one or two pairs of prompt jets or top quarks.

    hep-phhep-exJHEP(2018)·29 citations
18. 18*

    Direct photon production and PDF fits reloaded

    John M. Campbell🇺🇸 · Juan Rojo🇳🇱 · Emma Slade🇬🇧 · Ciaran Williams🇺🇸

    Direct photon production in hadronic collisions provides a handle on the gluon PDF by means of the QCD Compton scattering process. In this work we revisit the impact of direct photon production on a global PDF analysis, motivated by the recent availability of the next-to-next-to-leading (NNLO) calculation for this process. We demonstrate that the inclusion of NNLO QCD and leading-logarithmic electroweak corrections leads to a good quantitative agreement with the ATLAS measurements at 8 TeV and 13 TeV, except for the most forward rapidity region in the former case. By including the ATLAS 8 TeV direct photon production data in the NNPDF3.1 NNLO global analysis, we assess its impact on the medium-x gluon. We also study the constraining power of the direct photon production measurements on PDF fits based on different datasets, in particular on the NNPDF3.1 no-LHC and collider-only fits. We also present updated NNLO theoretical predictions for direct photon production at 13 TeV that include the constraints from the 8 TeV measurements.

    hep-phhep-exEPJC(2018)·60 citations
19. 19*

    On Non-slow Roll Inflationary Regimes

    Lilia Anguelova🇧🇬 · Peter Suranyi🇺🇸 · L.C. Rohana Wijewardhana🇺🇸

    We summarize our work on constant roll inflationary models. It was understood recently that constant roll inflation, in a regime beyond the slow roll approximation, can give models that are in agreement with the observational constraints. We describe a new class of constant roll inflationary models and investigate the behavior of scalar perturbations in them. We also comment on other non-slow roll regimes of inflation.

    ↳ hep-thastro-ph.COgr-qchep-phSpringer Proc.Math.Stat.(2017)·3 citations
20. 20*

    Dark energy scenario consistent with GW170817 in theories beyond Horndeski gravity

    Ryotaro Kase🇯🇵 · Shinji Tsujikawa🇯🇵

    The Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories up to quartic order are the general scheme of scalar-tensor theories allowing the possibility for realizing the tensor propagation speed $c_t$ equivalent to 1 on the isotropic cosmological background. We propose a dark energy model in which the late-time cosmic acceleration occurs by a simple k-essence Lagrangian analogous to the ghost condensate with cubic and quartic Galileons in the framework of GLPV theories. We show that a wide variety of the variation of the dark energy equation of state $w_{\mathrm{DE}}$ including the entry to the region $w_{\mathrm{DE}}<-1$ can be realized without violating conditions for the absence of ghosts and Laplacian instabilities. The approach to the tracker equation of state $w_{\mathrm{DE}}=-2$ during the matter era, which is disfavored by observational data, can be avoided by the existence of a quadratic k-essence Lagrangian $X^2$. We study the evolution of nonrelativistic matter perturbations for the model $c_t^2=1$ and show that the two quantities $\mu$ and $\Sigma$, which are related to the Newtonian and weak lensing gravitational potentials respectively, are practically equivalent to each other, such that $\mu \simeq \Sigma >1$. For the case in which the deviation of $w_{\mathrm{DE}}$ from $-1$ is significant at a later cosmological epoch, the values of $\mu$ and $\Sigma$ tend to be larger at low redshifts. We also find that our dark energy model can be consistent with the bounds on the deviation parameter ${\alpha }_{\mathrm{H}}$ from Horndeski theories arising from the modification of gravitational law inside massive objects.

    ↳ gr-qcastro-ph.COhep-phhep-thPRD(2018)·66 citations
21. 21*

    Holographic estimate of heavy quark diffusion in a magnetic field

    David Dudal🇧🇪 · Thomas G. Mertens🇧🇪

    We study the influence of a background magnetic field on the $J/\psi$ vector meson in a DBI-extension of the soft wall model, building upon our earlier work Phys. Rev. D91, 086002 (2015). In this specific holographic QCD model, we discuss the heavy quark number susceptibility and diffusion constants of charm quarks and their dependence on the magnetic field by either a hydrodynamic expansion or by numerically solving the differential equation. This allows us to determine the response of these transport coefficients to the magnetic field. The effects of the latter are considered both from a direct as indirect (medium) viewpoint. As expected, we find a magnetic field induced anisotropic diffusion, with a stronger diffusion in the longitudinal direction compared to the transversal one. We backup, at least qualitatively, our findings with a hanging string analysis of heavy quark diffusion in a magnetic field. From the quark number susceptibility we can extract an estimate for the effective deconfinement temperature in the heavy quark sector, reporting consistency with the phenomenon of inverse magnetic catalysis.

    ↳ hep-thhep-phPRD(2018)·53 citations
22. 22*

    A curvature bound from gravitational catalysis

    Holger Gies🇩🇪 · Riccardo Martini🇩🇪

    We determine bounds on the curvature of local patches of spacetime from the requirement of intact long-range chiral symmetry. The bounds arise from a scale-dependent analysis of gravitational catalysis and its influence on the effective potential for the chiral order parameter, as induced by fermionic fluctuations on a curved spacetime with local hyperbolic properties. The bound is expressed in terms of the local curvature scalar measured in units of a gauge-invariant coarse-graining scale. We argue that any effective field theory of quantum gravity obeying this curvature bound is safe from chiral symmetry breaking through gravitational catalysis and thus compatible with the simultaneous existence of chiral fermions in the low-energy spectrum. With increasing number of dimensions, the curvature bound in terms of the hyperbolic scale parameter becomes stronger. Applying the curvature bound to the asymptotic safety scenario for quantum gravity in four spacetime dimensions translates into bounds on the matter content of particle physics models.

    ↳ hep-thgr-qchep-phPRD(2018)·40 citations
23. 23*

    Event-by-Event Efficiency Fluctuations and Efficiency Correction for Cumulants of Superposed Multiplicity Distributions in Relativistic Heavy-ion Collision Experiments

    Shu He🇨🇳 · Xiaofeng Luo🇨🇳

    We performed systematic studies on the effects of event-by-event efficiency fluctuations on efficiency correction for cumulant analysis in relativistic heavy-ion collision experiments. Experimentally, particle efficiencies of events measured under different experimental conditions should be different. For fluctuation measurements, the final event-by-event multiplicity distributions should be the superposed distributions of various type of events measured under different conditions. We demonstrate efficiency fluctuation effects using numerical simulation, in which we construct an event ensemble consisting of events with two different efficiencies. By using the mean particle efficiencies, we find that the efficiency corrected cumulants show large deviations from the original inputs when the discrepancy between the two efficiencies is large. We further studied the effects of efficiency fluctuations for the cumulants of net-proton distributions by implementing the UrQMD events of Au+Au collisions at $\sqrt{s_{NN}}=7.7$ GeV in a realistic STAR detector acceptance. We consider the unequal efficiency in two sides of the Time Projection Chamber (TPC), multiplicity dependent efficiency, and the event-by-event variations of the collision vertex position along the longitudinal direction ($V_{\mathrm{z}}$). When the efficiencies fluctuate dramatically within the studied event sample, the effects of efficiency fluctuations have significant impacts on the efficiency corrections of cumulants with the mean efficiency. We find that this effect can be effectively suppressed by binning the entire event ensemble into various sub-event samples, in which the efficiency variations are relatively small. The final efficiency corrected cumulants can be calculated from the weighted average of the corrected factorial moments of the sub-event samples with the mean efficiency.

    ↳ physics.data-anhep-exhep-lathep-ph+2CPC(2018)·12 citations
24. 24*

    Chiral magnetic effect search in p(d)+Au, Au+Au collisions at RHIC

    Jie Zhao (for the STAR collaboration)🇺🇸

    The chiral magnetic effect (CME) refers to charge separation along a strong magnetic field of single-handed quarks, caused by interactions with topological gluon fields from QCD vacuum fluctuations. A major background of CME measurements in heavy-ion collisions comes from resonance decays coupled with elliptical flow anisotropy. These proceedings present two new studies from STAR to shed further light on the background issue: (1) small system p+Au and d+Au collisions where the CME signal is not expected, and (2) pair invariant mass dependence where resonance peaks can be identified.

    ↳ nucl-exhep-exhep-phnucl-thInt.J.Mod.Phys.Conf.Ser.(2018)·7 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.