Wed·Dec 7, 2016Wednesday·December 7, 2016

1. 01*

   Light Axial Vectors, Nuclear Transitions, and the ${}^8$Be Anomaly

   Jonathan Kozaczuk🇺🇸 · David E. Morrissey🇨🇦 · S. R. Stroberg🇨🇦

   New hidden particles could potentially be emitted and discovered in rare nuclear transitions. In this work we investigate the production of hidden vector bosons with primarily axial couplings to light quarks in nuclear transitions, and we apply our results to the recent anomaly seen in ${}^8$Be decays. The relevant matrix elements for ${}^8{\mathrm{Be}}^{\ast }(1^{+}){\to }^8\mathrm{Be}(0^{+})$ transitions are calculated using $abinitio$ methods with inter-nucleon forces derived from chiral effective field theory and the in-medium similarity renormalization group. We find that the emission of a light axial vector with mass $m_X\simeq 17\mathrm{MeV}$ can account for the anomaly seen in the $1^{+}\to 0^{+}$ isoscalar transition together with the absence of a significant anomaly in the corresponding isovector transition. We also show that such an axial vector can be derived from an anomaly-free ultraviolet-complete theory that is consistent with current experimental data.

   hep-phnucl-thPRD(2017)·92 citations
2. 02*

   Deep learning in color: towards automated quark/gluon jet discrimination

   Patrick T. Komiske🇺🇸 · Eric M. Metodiev🇺🇸 · Matthew D. Schwartz🇺🇸

   Artificial intelligence offers the potential to automate challenging data-processing tasks in collider physics. To establish its prospects, we explore to what extent deep learning with convolutional neural networks can discriminate quark and gluon jets better than observables designed by physicists. Our approach builds upon the paradigm that a jet can be treated as an image, with intensity given by the local calorimeter deposits. We supplement this construction by adding color to the images, with red, green and blue intensities given by the transverse momentum in charged particles, transverse momentum in neutral particles, and pixel-level charged particle counts. Overall, the deep networks match or outperform traditional jet variables. We also find that, while various simulations produce different quark and gluon jets, the neural networks are surprisingly insensitive to these differences, similar to traditional observables. This suggests that the networks can extract robust physical information from imperfect simulations.

   hep-phstat.MLJHEP(2017)·299 citations
3. 03*

   Neutrino oscillations in dense matter

   A.E. Lobanov🇷🇺

   We propose a modification of the electroweak theory, where the fermions with the same electroweak quantum numbers are combined in multiplets and are treated as different quantum states of a single particle. The developed approach enables one to calculate the probabilities of the processes taking place in the detector at long distances from the particle source. Calculations of higher-order processes including the computation of the contributions due to radiative corrections can be performed in the framework of the perturbation theory using the regular diagram technique. As a result, we obtain the analog to the Dirac--Schwinger equation of quantum electrodynamics describing neutrino oscillations and its spin rotation in dense matter.

   hep-phIzv.Vyssh.Uchebn.Zaved.Tomsk(2016)·9 citations
4. 04*

   Dark matter physics, flavor physics and LHC constraints in the dark matter model with a bottom partner

   Tomohiro Abe🇯🇵 · Junichiro Kawamura🇯🇵 · Shohei Okawa🇯🇵 · Yuji Omura🇯🇵

   In the scenario that a dark matter (DM) is a weakly interacting massive particle, there are many possibilities of the interactions with the Standard Model (SM) particles to achieve the relic density of DM. In this paper, we consider one simple DM model where the DM candidate is a complex scalar and interacts with the SM particles via exchange of the Higgs particle and an extra quark, named bottom partner. The extra quark carries the same quantum number as the right-handed down-type quarks and has Yukawa couplings with the DM candidate and the right-handed down-type quarks. The Yukawa interactions are not only relevant to the thermal relic density of the DM, but also contribute to the flavor physics, such as the $\Delta F=2$ processes. In addition, the flavor alignment of the Yukawa couplings is related to the decay modes of the extra quark. Then, we can find the explicit correlations among the physical observables in DM physics, flavor physics and the signals at the LHC. Based on the numerical analyses of the thermal relic density, the direct detection of the DM and the current LHC bounds using the latest results, we survey our predictions for the $\Delta F=2$ processes. We investigate the perturbative bound on the Yukawa coupling, as well. Study of a fermionic DM model with extra scalar quarks is also given for comparison.

   hep-phhep-exJHEP(2017)·13 citations
5. 05*

   Probing Lepton Flavor Violation at the 13 TeV LHC

   Reinard Primulando🇮🇩 · Patipan Uttayarat🇹🇭

   We investigate the bounds on tau-mu lepton flavor violation (LFV). Our main focus is on the collider constrains on tau-mu LFV. We use the Type-III Two-Higgs-Doublet-Model (2HDM) as a set up for our study. While the LFV branching fraction of the 125 GeV is well constrained by current LHC searches, the heavier neutral states could have a large branching fraction to tau and muon. We estimate the LHC reach for the 13 TeV center of mass energy with 300 ${\text{fb}}^{-1}$ luminosity for a neutral boson decaying into a tau and a muon. We identify parts of the LFV parameter space where the searches for heavy scalar and pseudoscalar decaying into a tau and a muon are more sensitive than the similar search for the 125 GeV boson.

   hep-phhep-exJHEP(2017)·25 citations
6. 06*

   Anatomy of chiral magnetic effect in and out of equilibrium

   Dmitri E. Kharzeev🇺🇸 · Mikhail A. Stephanov🇺🇸 · Ho-Ung Yee🇺🇸

   We identify a new contribution to the chiral magnetic conductivity at finite frequencies -- the magnetization current. This allows to quantitatively reproduce the known field-theoretic time-dependent (AC) chiral magnetic response in terms of kinetic theory. We evaluate the corresponding AC chiral magnetic conductivity in two flavor QCD plasma at weak coupling. The magnetization current results from the spin response of chiral quasiparticles to magnetic field, and is thus proportional to the quasiparticle's $g$-factor. In condensed matter systems, where the chiral quasi-particles are emergent and the $g$-factor can significantly differ from 2, this opens the possibility to tune the AC chiral magnetic response.

   hep-phcond-mat.mes-hallhep-thPRD(2017)·49 citations
7. 07*

   Coherent photoproductions of $J/\Psi$ and ${\rm Y}$ mesons in pp and PbPb ultraperipheral collisions from dynamical gluon distribution

   Qiang Fu🇨🇳 · Xurong Chen🇨🇳

   We present calculations of coherent photoproduction of vector mesons ($J/\Psi$ and ${\rm Y}$) with leading-order parton distribution functions to check new kinds of corrections of the DGLAP equations and nuclear modifications. The input gluon distribution of the proton is the dynamical parton model from the DGLAP equations with GLR-MQ-ZRS (Gribov-Levin-Ryskin, Mueller-Qiu, Zhu-Ruan-Shen) modifications. From comparison between several other gluon distribution models, we find that the dynamical gluon distribution fits with the results of meson photoproduction experiments in the high energy region. The calculation of the differential cross sections using dynamical and other gluon distributions is compared with the experimental data from the HERA, ZEUS and LHCb Collaborations. Although there is little data for the rapidity distribution of vector meson photoproduction near zero rapidity, the dynamical gluon distribution works well with the data in the large rapidity region.

   hep-phhep-exCPC(2017)·1 citation
8. 08*

   ${\alpha }_s$ in 2016 from the (revised) ALEPH data for $\tau$ decay

   Diogo Boito🇧🇷 · Maarten Golterman🇺🇸 · Kim Maltman🇦🇺 · Santiago Peris🇪🇸

   We summarize a comparison of the two strategies which are currently available in the literature for determining the value of ${\alpha }_s(m_{\tau })$. We will refer to these as the truncated Operator Product Expansion model and the Duality Violation model. After describing the main features of both approaches, we explain why the former fails to pass crucial tests. The latter, on the other hand, passes all the tests known up to date and, therefore, should be currently considered the only reliable method.

   hep-phhep-latPoS(2016)·1 citation
9. 09*

   $SU(3{)}^p$ Quiver Theories with $\mathcal{N}=0$ for $p=8$ and $9$

   Claudio Coriano🇮🇹 · Paul H. Frampton🇮🇹

   We close a gap in previous studies of nonsupersymmetric $\mathcal{N}=0$ quiver gauge theories from a phenomenological point of view aimed at acquiring specific proposals for models beyond the Standard Model (BSM). Because $SU(3)$ is the gauge group of QCD we fix $N=3$ and vary only the $Z_p$ abelian orbifold. The values $1\le p\le 7$ have been previously fully discussed as well as one special case, discovered by happenstance, of $p=12$. The values $p=8$ and $p=9$ are discussed comprehensively in the present paper including the electroweak mixing angle, gauge coupling unification, spontaneous symmetry breakdown to the standard model, and the occurrence of three quark-lepton families. Two promising quiver node identifications are discovered for $p=8$ and three for $p=9$. All of these merit further study as BSM candidates.

   hep-phPLB(2017)·0 citations
10. 10*

    Scheme variations of the QCD coupling

    Diogo Boito🇧🇷 · Matthias Jamin🇪🇸 · Ramon Miravitllas🇪🇸

    The Quantum Chromodynamics (QCD) coupling ${\alpha }_s$ is a central parameter in the Standard Model of particle physics. However, it depends on theoretical conventions related to renormalisation and hence is not an observable quantity. In order to capture this dependence in a transparent way, a novel definition of the QCD coupling, denoted by $\hat{a}$, is introduced, whose running is explicitly renormalisation scheme invariant. The remaining renormalisation scheme dependence is related to transformations of the QCD scale $\Lambda$, and can be parametrised by a single parameter $C$. Hence, we call $\hat{a}$ the $C$-scheme coupling. The dependence on $C$ can be exploited to study and improve perturbative predictions of physical observables. This is demonstrated for the QCD Adler function and hadronic decays of the $\tau$ lepton.

    hep-phEPJ Web Conf.(2017)·6 citations
11. 11*

    Search for anomalous tq$\gamma$ FCNC Couplings in direct single top quark production at the LHC

    Reza Goldouzian🇧🇪 · Barbara Clerbaux🇧🇪

    In this paper we propose and study direct single top quark production channel for probing the tq$\gamma$ flavor-changing neutral current (FCNC) interactions at the LHC. We reinterpret the experimental results of a search for direct single top quark production performed by ATLAS collaboration at 8 TeV to set upper bounds on the FCNC top quark decay branching fractions through the proposed channel, resulting in $\mathcal{B}$(t$\to$ u$\gamma$) $<$ 0.05\% and $\mathcal{B}$(t$\to$ c$\gamma$) $<$ 0.14\%. Finally, the expected sensitivity at 13 TeV for various integrated luminosity scenarios is estimated.

    hep-phhep-ex3 citations
12. 12*

    Probing CP-violating Higgs and gauge boson couplings in the Standard Model effective field theory

    Felipe Ferreira🇬🇧 · Benjamin Fuks🇫🇷 · Veronica Sanz🇬🇧 · Dipan Sengupta🇫🇷

    We study the phenomenological consequences of several $CP$-violating structures that could arise in the Standard Model effective field theory framework. Focusing on operators involving electroweak gauge and/or Higgs bosons, we derive constraints originating from Run I LHC data. We then study the capabilities of the present and future LHC runs at higher energies to further probe associated CP-violating phenomena and we demonstrate how differential information can play a key role. We consider both traditional four-lepton probes of CP-violation in the Higgs sector and novel new physics handles based on varied angular and non-angular observables.

    hep-phEPJC(2017)·50 citations
13. 13*

    Exotic Signals of Vectorlike Quarks

    Bogdan A. Dobrescu🇺🇸 · Felix Yu🇩🇪

    Vectorlike fermions are an important target for hadron collider searches. We show that the vectorlike quarks may predominantly decay via higher-dimensional operators into a quark plus a couple of other Standard Model fermions. Pair production of vectorlike quarks of charge 2/3 at the LHC would then lead to a variety of possible final states, including $t\bar{t}+4\tau$, $t\bar{b}\nu +3\tau$, $t\bar{t}+4\mu$, $t\bar{b}\nu +3\mu$ or $t\bar{t}+4b$. Additional channels ($b\bar{b}+4\tau$, $6b$, etc.) arise in the case of a vectorlike quark of charge $-1/3$. If the vectorlike quark decays into three light quarks, then the $(3j)(3j)$ signal is more difficult to observe, and the vectorlike quark mass is almost unconstrained by current searches.

    hep-phJ.Phys.G(2018)·35 citations
14. 14*

    Next-to-leading order corrections to deeply virtual production of pseudoscalar mesons

    G. Duplančić🇭🇷 · D. Müller🇭🇷 · K. Passek-Kumerički🇭🇷

    We complete the perturbative next-to-leading order corrections to the hard scattering amplitudes of deeply virtual meson leptoproduction processes at leading twist-two level by presenting the results for the production of flavor singlet pseudoscalar mesons. The new results are given in the common momentum fraction representation and in terms of conformal moments. We also comment on the flavor singlet results for deeply virtual vector meson production.

    hep-phPLB(2017)·19 citations
15. 15*

    Dark matter substructure cannot explain properties of the Fermi Galactic Centre excess

    Hamish A. Clark🇦🇺 · Pat Scott🇬🇧 · Roberto Trotta🇬🇧 · Geraint F. Lewis🇦🇺

    An excess of gamma rays has been identified at the centre of the Milky Way, and annihilation of dark matter has been posited as a potential source. This hypothesis faces significant challenges: difficulty characterizing astrophysical backgrounds, the need for a non-trivial adiabatic contraction of the inner part of the Milky Way's dark matter halo, and recent observations of photon clustering, which suggest that the majority of the excess is due to unresolved point sources. Here we point out that the apparent point-like nature of the emission rules out the dark matter interpretation of the excess entirely. Attempting to model the emission with dark matter point sources either worsens the problem with the inner slope, requires an unrealistically large minihalo fraction toward the Galactic Centre, or overproduces the observed emission at higher latitudes.

    ↳ astro-ph.HEastro-ph.COhep-phJCAP(2018)·26 citations
16. 16*

    Lattice QCD spectroscopy for hadronic CP violation

    Jordy de Vries🇳🇱 · Emanuele Mereghetti🇺🇸 · Chien-Yeah Seng🇨🇳 · Andre Walker-Loud🇺🇸

    The interpretation of nuclear electric dipole moment (EDM) experiments is clouded by large theoretical uncertainties associated with nonperturbative matrix elements. In various beyond-the-Standard Model scenarios nuclear and diamagnetic atomic EDMs are expected to be dominated by CP-violating pion-nucleon interactions that arise from quark chromo-electric dipole moments. The corresponding CP-violating pion-nucleon coupling strengths are, however, poorly known. In this work we propose a strategy to calculate these couplings by using spectroscopic lattice QCD techniques. Instead of directly calculating the pion-nucleon coupling constants, a challenging task, we use chiral symmetry relations that link the pion-nucleon couplings to nucleon sigma terms and mass splittings that are significantly easier to calculate. In this work, we show that these relations are reliable up to next-to-next-to-leading order in the chiral expansion in both SU(2) and SU(3) chiral perturbation theory. We conclude with a brief discussion about practical details regarding the required lattice QCD calculations and the phenomenological impact of an improved understanding of CP-violating matrix elements.

    ↳ hep-lathep-phnucl-thPLB(2017)·47 citations
17. 17*

    Is String Phenomenology an Oxymoron?

    Fernando Quevedo🇮🇹

    A brief discussion is presented assessing the achievements and challenges of string phenomenology: the subfield dedicated to study the potential for string theory to make contact with particle physics and cosmology. Building from the well understood case of the standard model as a very particular example within quantum field theory we highlight the very few generic observable implications of string theory, most of them inaccessible to low-energy experiments, and indicate the need to extract concrete scenarios and classes of models that could eventually be contrasted with searches in collider physics and other particle experiments as well as in cosmological observations. The impact that this subfield has had in mathematics and in a better understanding of string theory is emphasised as spin-offs of string phenomenology. Moduli fields, measuring the size and shape of extra dimensions, are highlighted as generic low-energy remnants of string theory that can play a key role for supersymmetry breaking as well as for inflationary and post-inflationary early universe cosmology. It is argued that the answer to the question in the title should be, as usual, {\it No}. Future challenges for this field are briefly mentioned. This essay is a contribution to the conference: "Why Trust a Theory?", Munich, December 2015.

    ↳ hep-thhep-ph16 citations
18. 18*

    Quasi parton distributions and the gradient flow

    Christopher Monahan🇺🇸 · Kostas Orginos🇺🇸

    We propose a new approach to determining quasi parton distribution functions (PDFs) from lattice quantum chromodynamics. By incorporating the gradient flow, this method guarantees that the lattice quasi PDFs are finite in the continuum limit and evades the thorny, and as yet unresolved, issue of the renormalization of quasi PDFs on the lattice. In the limit that the flow time is much smaller than the length scale set by the nucleon momentum, the moments of the smeared quasi PDF are proportional to those of the light-front PDF. We use this relation to derive evolution equations for the matching kernel that relates the smeared quasi PDF and the light-front PDF. As part of this discussion, we elucidate the relationship between the quasi and light-front PDFs.

    ↳ hep-lathep-phJHEP(2017)·97 citations
19. 19*

    Scientific Biography of Stanley Mandelstam, Part I: 1955-1980

    Charles B. Thorn🇺🇸

    I review Stanley Mandelstam's many contributions to particle physics, quantum field theory and string theory covering the years 1955 through 1980. His more recent work will be reviewed by Nathan Berkovits. This is my contribution to the Memorial Volume for Stanley Mandelstam (World Scientific, 2017).

    ↳ hep-thhep-phphysics.hist-phInt.J.Mod.Phys.A(2017)·1 citation
20. 20*

    Prospects for rare and forbidden hyperon decays at BESIII

    Hai-Bo Li🇨🇳

    The study of hyperon decays at the Beijing Electron Spectrometer III (BESIII) is proposed to investigate the events of $J/\psi$ decay into hyperon pairs, which provide a pristine experimental environment at the Beijing Electron--Positron Collider II. About $10^6$--$10^8$ hyperons, i.e., $\Lambda$, $\Sigma$, $\Xi$, and $\Omega$, will be produced in the $J/\psi$ and $\psi (2S)$ decays with the proposed data samples at BESIII. Based on these samples, the measurement sensitivity of the branching fractions of the hyperon decays is in the range of $10^{-5}$--$10^{-8}$. In addition, with the known center-of-mass energy and "tag technique," rare decays and decays with invisible final states can be probed.

    ↳ hep-exhep-phFront.Phys.(2017)·85 citations
21. 21*

    SQM2016: Theory Summary

    V. Greco🇮🇹

    This is an overview of the main theoretical developments presented at SQM2016 held in Berkeley, California (USA) in June 2015.

    ↳ nucl-thhep-phnucl-exJ.Phys.Conf.Ser.(2017)·3 citations
22. 22*

    On the nature of some SGRs and AXPs as rotation-powered neutron stars

    Jaziel G. Coelho🇮🇹 · D. L. Cáceres · R. C. R. de Lima🇧🇷 · M. Malheiro🇧🇷 · J. A. Rueda🇮🇹 · R. Ruffini🇮🇹

    We investigate the possibility that some SGRs/AXPs could be canonical rotation-powered pulsars using realistic NS structure parameters instead of fiducial values. We show that realistic NS parameters lowers the estimated value of the magnetic field and radiation efficiency, $L_X/{\dot{E}}_{\mathrm{rot}}$, with respect to estimates based on fiducial NS parameters. We show that nine SGRs/AXPs can be described as canonical pulsars driven by the NS rotational energy, for $L_X$ computed in the soft (2--10~keV) X-ray band. We compute the range of NS masses for which $L_X/{\dot{E}}_{\mathrm{rot}}<1$. We discuss the observed hard X-ray emission in three sources of the group of nine potentially rotation-powered NSs. This additional hard X-ray component dominates over the soft one leading to $L_X/{\dot{E}}_{\mathrm{rot}}>1$ in two of them. We show that 9 SGRs/AXPs can be rotation-powered NSs if we analyze their X-ray luminosity in the soft 2--10~keV band. Interestingly, four of them show radio emission and six have been associated with supernova remnants (including Swift J1834.9-0846 the first SGR observed with a surrounding wind nebula). These observations give additional support to our results of a natural explanation of these sources in terms of ordinary pulsars. Including the hard X-ray emission observed in three sources of the group of potential rotation-powered NSs, this number of sources with $L_X/{\dot{E}}_{\mathrm{rot}}<1$ becomes seven. It remains open to verification 1) the accuracy of the estimated distances and 2) the possible contribution of the associated supernova remnants to the hard X-ray emission.

    ↳ astro-ph.HEastro-ph.SRhep-phnucl-thAstron.Astrophys.(2017)·17 citations
23. 23*

    Evidence of effective axial U(1) symmetry restoration at high temperature QCD

    A. Tomiya🇨🇳 · G. Cossu🇬🇧 · S. Aoki🇯🇵 · H. Fukaya🇯🇵 · S. Hashimoto🇯🇵 · T. Kaneko🇯🇵 · J. Noaki🇯🇵

    We study the axial U(1) symmetry at finite temperature in two-flavor lattice QCD. Employing the Mobius domain-wall fermions, we generate gauge configurations slightly above the critical temperature Tc with different lattice sizes L = 2-4 fm. Our action allows frequent topology tunneling while keeping good chiral symmetry close enough to that of overlap fermions. This allows us to recover full chiral symmetry by an overlap/domain-wall reweighting. Above the phase transition, a strong suppression of the low-lying modes is observed in both of overlap and domain-wall Dirac spectra. We, however, find a sizable violation of the Ginsparg-Wilson relation in the Mobius domain-wall Dirac eigenmodes, which dominates the signals of the axial U(1) symmetry breaking near the chiral limit. We also find that the use of overlap fermion only in the valence sector is dangerous since it suffers from the artifacts due to partial quenching. Reweighting the Mobius domain-wall fermion determinant to that of the overlap fermion, we observe the axial U(1) breaking to vanish in the chiral limit, which is stable against the changes of the lattice volume and lattice spacing.

    ↳ hep-lathep-phhep-thnucl-thPRD(2017)·148 citations
24. 24*

    Probing QCD perturbation theory at high energies with continuum extrapolated lattice data

    Stefan Sint (ALPHA collaboration)🇮🇪

    Precision tests of QCD perturbation theory are not readily available from experimental data. The main reasons are systematic uncertainties due to the confinement of quarks and gluons, as well as kinematical constraints which limit the accessible energy scales. We here show how continuum extrapolated lattice data may overcome such problems and provide excellent probes of renormalized perturbation theory. This work corresponds to an essential step in the ALPHA collaboration's project to determine the $\Lambda$-parameter in 3-flavour QCD. I explain the basic techniques used in the high energy regime, namely the use of mass-independent renormalization schemes for the QCD coupling constant in a finite Euclidean space time volume. When combined with finite size techniques this allows one to iteratively step up the energy scale by factors of 2, thereby quickly covering two orders of magnitude in scale. We may then compare perturbation theory (with $\beta$-functions available up to 3-loop order) to our non-perturbative data for a 1-parameter family of running couplings. We conclude that a target precision of 3 percent for the $\Lambda$-parameter requires non-perturbative data up to scales where ${\alpha }_s\approx 0.1$, whereas the apparent precision obtained from applying perturbation theory around ${\alpha }_s\approx 0.2$ can be misleading. This should be taken as a general warning to practitioners of QCD perturbation theory.

    ↳ hep-lathep-phEPJ Web Conf.(2017)·0 citations

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