Tue·Aug 30, 2016Tuesday·August 30, 2016

1. 01*

   Energy dependence of dissociative $J/\psi$ photoproduction as a signature of gluon saturation at the LHC

   J. Cepila (1)🇨🇿 · J. G. Contreras (1)🇨🇿 · J. D. Tapia Takaki (2) ((1) Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Czech Republic, (2) Department of Physics and Astronomy, The University of Kansas, Lawrence, KS, USA)🇺🇸

   We have developed a model in which the quantum fluctuations of the proton structure are characterised by hot spots, whose number grows with decreasing Bjorken-$x$. Our model reproduces the $F_2(x,Q^2)$ data from HERA at the relevant scale, as well as the exclusive and dissociative $J/\psi$ photoproduction data from H1 and ALICE. Our model predicts that for $W_{\gamma \mathrm{p}}\approx 500$ GeV, the dissociative $J/\psi$ cross section reaches a maximum and then decreases steeply with energy, which is in qualitatively good agreement to a recent observation that the dissociative $J/\psi$ background in the exclusive $J/\psi$ sample measured in photoproduction by ALICE decreases as energy increases. Our prediction provides a clear signature for gluon saturation at LHC energies.

   hep-phPLB(2017)·109 citations
2. 02*

   The Vev Flip-Flop: Dark Matter Decay between Weak Scale Phase Transitions

   Michael J. Baker🇩🇪 · Joachim Kopp🇩🇪

   We propose a new alternative to the Weakly Interacting Massive Particle (WIMP) paradigm for dark matter. Rather than being determined by thermal freeze-out, the dark matter abundance in this scenario is set by dark matter decay, which is allowed for a limited amount of time just before the electroweak phase transition. More specifically, we consider fermionic singlet dark matter particles coupled weakly to a scalar mediator $S_3$ and to auxiliary dark sector fields, charged under the Standard Model gauge groups. Dark matter freezes out while still relativistic, so its abundance is initially very large. As the Universe cools down, the scalar mediator develops a vacuum expectation value (vev), which breaks the symmetry that stabilises dark matter. This allows dark matter to mix with charged fermions and decay. During this epoch, the dark matter abundance is reduced to give the value observed today. Later, the SM Higgs field also develops a vev, which feeds back into the $S_3$ potential and restores the dark sector symmetry. In a concrete model we show that this "vev flip-flop" scenario is phenomenologically successful in the most interesting regions of its parameter space. We also comment on detection prospects at the LHC and elsewhere.

   hep-phPRL(2017)·66 citations
3. 03*

   Palatable Leptoquark Scenarios for Lepton Flavor Violation in Exclusive $b\to s{\ell }_1{\ell }_2$ modes

   Damir Bečirević🇫🇷 · Nejc Košnik🇸🇮 · Olcyr Sumensari🇫🇷 · Renata Zukanovich Funchal🇧🇷

   We examine various scenarios that involve a light $\mathcal{O}(1TeV)$ leptoquark state and select those which are compatible with the current experimental values for $\mathcal{B}(B_s\to \mu \mu )$, $\mathcal{B}(B\to K\mu \mu {)}_{\mathrm{large}-q^2}$, $R_K={\mathcal{B}}^{\prime }(B\to K\mu \mu )/{\mathcal{B}}^{\prime }(B\to Kee)$, and which lead to predictions consistent with other experimental data. We show that two such scenarios are phenomenologically plausible, namely the one with a doublet of scalar leptoquarks of hypercharge $1/6$, and the one with a triplet of vector leptoquarks of hypercharge $2/3$. We also argue that a model with a singlet scalar leptoquark of hypercharge $1/3$ is not viable. Using the present experimental data as constraints, it is shown that the exclusive lepton flavor violating decays, $\mathcal{B}(B_s\to \mu \tau )$, $\mathcal{B}(B\to K\mu \tau )$ and $\mathcal{B}(B\to K^{\ast }\mu \tau )$, can be as large as $\mathcal{O}(10^{-5})$.

   hep-phhep-exhep-latJHEP(2016)·214 citations
4. 04*

   Baryons in the unquenched quark model

   R. Bijker🇲🇽 · S. Diaz-Gomez🇲🇽 · M.A. Lopez-Ruiz🇺🇸 · E. Santopinto🇮🇹

   In this contribution, we present the unquenched quark model as an extension of the constituent quark model that includes the effects of sea quarks via a ${}^3{P}_0$ quark-antiquark pair-creation mechanism. Particular attention is paid to the spin and flavor content of the proton, magnetic moments and $\beta$ decays of octet baryons.

   hep-phhep-exnucl-exnucl-thAIP Conf.Proc.(2016)·1 citation
5. 05*

   Reconstructing parton densities at large fractional momenta

   Alessandro Bacchetta🇮🇹 · Marco Radici🇮🇹 · Barbara Pasquini🇮🇹 · Xiaonu Xiong🇮🇹

   Parton distribution functions (PDFs) are nonperturbative objects defined by nonlocal light-cone correlations. They cannot be computed directly from Quantum Chromodynamics (QCD). Using a standard lattice QCD approach, it is possible to compute moments of PDFs, which are matrix elements of local operators. Recently, an alternative approach has been proposed, based on the introduction of quasi-parton distribution functions (quasi-PDFs), which are matrix elements of equal-time spatial correlations and hence calculable on lattice. Quasi-PDFs approach standard PDFs in the limit of very large longitudinal proton momenta $P^z$. This limit is not attainable in lattice simulations, and quasi-PDFs fail to reproduce PDFs at high fractional longitudinal momenta. In this paper, we propose a method to improve the reconstruction of PDFs by combining information from quasi-PDFs and from the Mellin moments of regular PDFs. We test our method using the diquark spectator model for up and down valence distributions of both unpolarized and helicity PDFs. In the future, the method can be used to produce PDFs entirely based on lattice QCD results.

   hep-phhep-exnucl-exnucl-thPRD(2017)·20 citations
6. 06*

   Duality between chiral symmetry breaking and charged pion condensation at large $N_c$: Consideration of an NJL${}_2$ model with baryon-, isospin- and chiral isospin chemical potentials

   D. Ebert🇩🇪 · T.G. Khunjua🇷🇺 · K.G. Klimenko🇷🇺

   In this paper we investigate the phase structure of a (1+1)-dimensional schematic quark model with four-quark interaction and in the presence of baryon (${\mu }_B$), isospin (${\mu }_I$) and chiral isospin (${\mu }_{I5}$) chemical potentials. It is established that in the large-$N_c$ limit ($N_c$ is the number of colored quarks) there exists a duality correspondence between the chiral symmetry breaking phase and the charged pion condensation (PC) one. The role and influence of this property on the phase structure of the model are studied. Moreover, it is shown that the chemical potential ${\mu }_{I5}$ promotes the appearance of the charged PC phase with nonzero baryon density.

   hep-phhep-thPRD(2016)·27 citations
7. 07*

   Lagrangian magnetic moment from polarization

   Fabio L. Braghin🇧🇷

   An effective Lagrangian term for the electron magnetic moment, and more generally electromagnetic form factors, is calculated by considering the background field method. Two Fierz transformations are performed for a one-photon exchange interaction, and the ambiguity in doing such transformations is exploited. The resulting effective interaction may exhibit an approximated rotational chiral symmetry either for the scalar-pseudoscalar currents interaction or for the vector-axial currents interaction. The leading terms in the expansion of the fermion determinant yield the leading QED effective action with the complete one loop electromagnetic form factors. A model is proposed to produce the tree level magnetic moment term.

   hep-phhep-thnucl-th0 citations
8. 08*

   CP sensitive observables of a hypothetical heavy spin-0 particle with $\gamma \gamma -$interactions dominant

   N.Belyaev🇷🇺 · R.Konoplich🇺🇸 · K.Prokofiev🇨🇳

   We study observables sensitive to tensor structure of interactions of a hypothetical heavy spin-0 particle. It is assumed that the interactions of this particle are primary with photons; interactions with vector bosons $gg$, $WW$, $ZZ$, and quarks $t\bar{t}$ are suppressed. The above assumptions favor the production of this hypothetical particle through the vector boson fusion mechanism structurally dominated by $\gamma \gamma$ and $\gamma Z$ interactions. This particle will be produced in association with two light quarks. It is shown that the difference in azimuthal angle between the tagging jets provides an observable sensitive to the CP properties of this hypothetical particle.

   hep-phPhys.Atom.Nucl.(2018)·3 citations
9. 09*

   A light front quark-diquark model for the nucleons

   Tanmay Maji🇮🇳 · Dipankar Chakrabarti🇮🇳

   We present a quark-diquark model for the nucleons where the light front wave functions are constructed from the soft-wall AdS/QCD prediction. The model is consistent with quark counting rule and Drell-Yan-West relation. The model reproduces the scale evolution of unpolarized PDF of proton for a wide range of energy scale. Helicity and transversity distributions for the proton predicted in this model agree with phenomenological fits. The axial and tensor charges are also shown to agree with the experimental data. The model can be used to evaluate distributions like GPDS, TMDs etc. and their scale evolutions.

   hep-phPRD(2016)·74 citations
10. 10*

    Standard Model as the topological material

    G.E. Volovik🇫🇮 · M.A. Zubkov🇷🇺

    Study of the Weyl and Dirac topological materials (topological semimetals, insulators, superfluids and superconductors) opens the route for the investigation of the topological quantum vacua of relativistic fields. The symmetric phase of the Standard Model (SM), where both electroweak and chiral symmetry are not broken, represents the topological semimetal. The vacua of the SM (and its extensions) in the phases with broken Electroweak symmetry represent the topological insulators of different types. We discuss in details the topological invariants in both symmetric and broken phases and establish their relation to the stability of vacuum.

    hep-phcond-mat.otherNew J.Phys.(2017)·23 citations
11. 11*

    Charged Lepton Flavor-violating Transitions in Color Octet Model

    Bin Li (Nankai U.)🇨🇳 · Yi Liao (Nankai U., ITP, CAS, CHEP, Peking U.)🇨🇳 · Xiao-Dong Ma (Nankai U.)🇨🇳

    We study charged lepton flavor-violating (LFV) transitions in the color octet model that generates neutrino mass and lepton mixing at one loop. By taking into account neutrino oscillation data and assuming octet particles of TeV scale mass, we examine the feasibility to detect these transitions in current and future experiments. We find that for general values of parameters the branching ratios for LFV decays of the Higgs and $Z$ bosons are far below current and even future experimental bounds. For LFV transitions of the muon, the present bounds can be satisfied generally, while future sensitivities could distinguish between the singlet and triplet color-octet fermions. The triplet case could be ruled out by future $\mu -e$ conversion in nuclei, and for the singlet case the conversion and the decays $\mu \to 3e,e\gamma$ play complementary roles in excluding relatively low mass regions of the octet particles.

    hep-phEPJC(2016)·2 citations
12. 12*

    Constraining high energy interaction mechanisms by studying forward hadron production at the LHC

    S. Ostapchenko🇩🇪 · M. Bleicher🇩🇪 · T. Pierog🇩🇪 · K. Werner🇫🇷

    We demonstrate that underlying assumptions concerning the structure of constituent parton Fock states in hadrons make a strong impact on the predictions of hadronic interaction models for forward hadron spectra and for long-range correlations between central and forward hadron production. Our analysis shows that combined studies of proton-proton collisions at the Large Hadron Collider by central and forward-looking detectors have a rich potential for discriminating between the main model approaches.

    hep-phPRD(2016)·24 citations
13. 13*

    The axial charges of the hidden-charm pentaquark states

    Guang-Juan Wang🇨🇳 · Zhan-Wei Liu🇦🇺 · Shi-Lin Zhu🇨🇳

    With the chiral quark model, we have calculated the axial charges of the pentaquark states with $(I,I_3)=(\frac{1}{2},\frac{1}{2})$ and $J^P={\frac{1}{2}}^{\pm },{\frac{3}{2}}^{\pm },{\frac{5}{2}}^{\pm }$. The $P_c$ states with the same $J^P$ quantum numbers but different color-spin-flavor configurations have very different axial charges, which encode important information on their underlying structures. For some of the $J^P={\frac{3}{2}}^{\pm }$ or ${\frac{5}{2}}^{\pm }$ pentaquark states, their axial charges are much smaller than that of the proton.

    hep-phhep-exnucl-thPRC(2016)·3 citations
14. 14*

    Loop effects of heavy new scalars and fermions in $b\to s{\mu }^{+}{\mu }^{-}$

    Pere Arnan🇪🇸 · Andreas Crivellin🇨🇭 · Lars Hofer🇪🇸 · Federico Mescia🇪🇸

    Recent measurements of $b\to s{\mu }^{+}{\mu }^{-}$ processes at LHCb and BELLE have revealed tensions at the $2-3\sigma$ level between the Standard Model (SM) prediction and the experimental results in the channels $B\to K^{\ast }{\mu }^{+}{\mu }^{-}$ and $B_s\to \varphi {\mu }^{+}{\mu }^{-}$, as well as in the lepton-flavor universality violating observable $R_K=\mathrm{Br}(B\to K{\mu }^{+}{\mu }^{-})/\mathrm{Br}(B\to K{e}^{+}{e}^{-}$). Combined global fits to the available $b\to s{\mu }^{+}{\mu }^{-}$ data suggest that these tensions might have their common origin in New Physics (NP) beyond the SM because some NP scenarios turn out to be preferred over the SM by $4-5\sigma$. The fact that all these anomalies are related to muons further suggests a connection (and a common NP explanation) with the long-standing anomaly in the anomalous magnetic moment of the muon, $a_{\mu }$. In this article, we study the impact of a generic class of NP models featuring new heavy scalars and fermions that couple to the SM fermions via Yukawa-like interactions. We consider two different scenarios, introducing either one additional fermion and two scalars or two additional fermions and one scalar, and examine all possible representations of the new particles under the SM gauge group with dimension up to the adjoint one. The models induce one-loop contributions to $b\to s{\mu }^{+}{\mu }^{-}$ and $a_{\mu }$ which are capable of solving the respective anomalies at the $2\sigma$ level, albeit a relatively large coupling of the new particles to muons is required. In the case of $b\to s{\mu }^{+}{\mu }^{-}$, stringent constraints from $B_s-{\overline{B}}_s$ mixing arise which can be relaxed if the new fermion is a Majorana particle.

    hep-phhep-exJHEP(2017)·126 citations
15. 15*

    Lorentz-violating spinor electrodynamics and Penning traps

    Yunhua Ding🇺🇸 · Alan Kostelecky🇺🇸

    The prospects are explored for testing Lorentz- and CPT-violating quantum electrodynamics in experiments with Penning traps. We present the Lagrange density of Lorentz-violating spinor electrodynamics with operators of mass dimensions up to six, and we discuss some of its properties. The theory is used to derive Lorentz- and CPT-violating perturbative shifts of the energy levels of a particle confined to a Penning trap. Observable signals are discussed for trapped electrons, positrons, protons, and antiprotons. Existing experimental measurements on anomaly frequencies are used to extract new or improved bounds on numerous coefficients for Lorentz and CPT violation, using sidereal variations of observables and comparisons between particles and antiparticles.

    hep-phPRD(2016)·132 citations
16. 16*

    Universal limiting pressure for a three-flavor color superconducting PNJL model phase diagram

    A. Ayriyan🇷🇺 · J. Berdermann🇩🇪 · D. Blaschke🇷🇺 · R. Lastowiecki🇵🇱

    The phase diagram of a three-flavor Polyakov-loop Nambu-Jona-Lasinio model is analyzed for the case of isospin symmetric matter with color superconducting phases. The coexistence of chiral symmetry breaking and two-flavor color superconductivity (2SC phase) and a thermodynamic instability due to the implementation of a color neutrality constraint is observed. It is suggested to use a universal hadronization pressure to estimate the phase border between hadronic and quark-gluon plasma phases. Trajectories of constant entropy per baryon are analyzed for conditions appropriate for heavy-ion collisions in the NICA-FAIR energy range.

    hep-phnucl-th3 citations
17. 17*

    $X(4140)$, $X(4270)$, $X(4500)$ and $X(4700)$ and their $cs\bar{c}\bar{s}$ tetraquark partners

    Jing Wu🇨🇳 · Yan-Rui Liu🇨🇳 · Kan Chen🇨🇳 · Xiang Liu🇨🇳 · Shi-Lin Zhu🇨🇳

    In the simple color-magnetic interaction model, we investigate possible ground $cs\bar{c}\bar{s}$ tetraquark states in the diquark-antidiquark basis. We use several methods to estimate the mass spectrum and discuss possible assignment for the $X$ states observed in the $J/\psi \varphi$ channel. We find that assigning the Belle $X(4350)$ as a $0^{++}$ tetraquark is consistent with the tetraquark interpretation for the $X(4140)$ and $X(4270)$ while the interpretation of the $X(4500)$ and $X(4700)$ needs orbital or radial excitation. There probably exist several tetraquarks around 4.3 GeV that decay into $J/\psi \varphi$ or ${\eta }_c\varphi$.

    hep-phhep-exhep-latnucl-ex+1PRD(2016)·69 citations
18. 18*

    Susceptibilities of Conserved Charges within a Modified Nambu-Jona-Lasinio Model

    Wenkai Fan🇨🇳 · Xiaofeng Luo🇨🇳 · Hong-Shi Zong🇨🇳

    We evaluate the $2$nd to $4$th order baryon, charge and strangeness susceptibilities near a chiral critical point using the Nambu--Jona--Lasinio model under different temperature and baryon chemical potential. Baryon number susceptibilities are found to be of the greatest magnitude, offering the strongest signal. Whereas the strangeness susceptibilities have the smallest divergence dominating area, owing to the large strange quark mass. We also make an attempt to compare our results with experiment data. The trend at high collision energy are found to be consistent between theory and experiment. The model calculation predicts more complex behavior at low collision energies, near the postulated critical end point.

    hep-phInt.J.Mod.Phys.A(2017)·36 citations
19. 19*

    Examining a possible cascade effect in chiral symmetry breaking

    Amir H. Fariborz🇺🇸 · Renata Jora🇷🇴

    We examine a toy model and a cascade effect for confinement and chiral symmetry breaking which consists in several phase transitions corresponding to the formation of bound states and chiral condensates with different number of fermions for a strong group. We analyze two examples: regular QCD where we calculate the "four quark" vacuum condensate and a preon composite model based on QCD at higher scales. In this context we also determine the number of flavors at which the second chiral and confinement phase transitions occur and discuss the consequences.

    hep-phMod.Phys.Lett.A(2016)·1 citation
20. 20*

    Searching for SUSY and decaying gravitino DM at the LHC and Fermi-LAT with the $\mu \nu$SSM

    Carlos Muñoz🇪🇸

    The `$\mu$ from $\nu$' supersymmetric standard model ($\mu \nu$SSM) solves the $\mu$ problem of supersymmetric models and reproduces neutrino data, simply using couplings with the three families of right-handed neutrinos $\nu$'s. Novel signatures of supersymmetry at the LHC are expected through these new states, and couplings breaking $R$ parity. All supersymmetric particles are potential candidates for the lightest one, which is not stable leading to prompt or displaced vertices and producing final states with multi-leptons/taus/jets/photons and missing energy. Besides, a decaying gravitino turns out to be an interesting candidate for dark matter. It can be searched through gamma-ray observations, such as those of the Fermi Large Area Telescope. The latter, depending on the region of the parameter space of the model, already imposes an upper bound on the gravitino mass of the order of $5-20$ GeV and a lower bound on the lifetime of about $10^{25-28}$ s.

    hep-phastro-ph.HEPoS(2016)·11 citations
21. 21*

    Spin measurements in strangeness production at the LHC

    S.M. Troshin🇷🇺 · N.E. Tyurin🇷🇺

    We briefly recollect the problem of significant hyperon polarization emphasizing the role of spin in dynamics of hadron interactions. We provide also some model predictions based on chiral dynamics and the impact parameter picture for illustration. The old, but yet unsolved problem of hyperon polarization, can obtain a new insight from the measurements at the LHC energies and, in combination with other measurements, can be used for tagging QGP formation in $pp$--collisions.

    hep-ph1 citation
22. 22*

    Open charm contributions to the E1 transitions of $\psi (3686)$ and $\psi (3770)\to \gamma {\chi }_{cJ}$

    Zheng Cao🇨🇳 · Martin Cleven🇪🇸 · Qian Wang🇩🇪 · Qiang Zhao🇨🇳

    The E1 transitions of $\psi (3686)$ and $\psi (3770)\to \gamma {\chi }_{cJ}$ are investigated in a non-relativistic effective field theory (NREFT) where the open charm effects are included systematically as the leading corrections. It also allows a self-consistent inclusion of the $S$-$D$ mixing in the same framework. We are able to show that the open charm contributions are essential for understanding the significant discrepancies between the non-relativistic leading order calculations and the experimental data.

    hep-phEPJC(2016)·10 citations
23. 23*

    The cancellation mechanism in the predictions of electric dipole moments

    Ligong Bian🇨🇳 · Ning Chen🇨🇳

    The interpretation of the baryon asymmetry of the Universe necessitates the CP violation beyond the Standard Model (SM). We present a general cancellation mechanism in the theoretical predictions of the electron electric dipole moments (EDM), quark chromo-EDMs, and Weinberg operators. A relative large CP violation in the Higgs sector is allowed by the current electron EDM constraint released by the ACME collaboration in 2013, and the recent ${}^{199}$Hg EDM experiment. The cancellation mechanism can be induced by the mass splitting of heavy Higgs bosons around $\sim \mathcal{O}(0.1-1)$ GeV, and the extent of the mass degeneracy determines the magnitude of the CP-violating phase. We explicate this point by investigating the CP-violating two-Higgs-doublet model and the minimal supersymmetric Standard Model. The cancellation mechanism is general when there are CP violation and mixing in the Higgs sector of new physics models. The CP-violating phases in this scenario can be excluded or detected by the projected ${}^{225}$Ra EDM experiments with precision reaching $\sim 10^{-28}e\cdot \mathrm{cm}$, as well as the future colliders.

    hep-phhep-exPRD(2017)·26 citations
24. 24*

    Lorentz symmetry violating low energy dispersion relations from a dimension-five photon scalar mixing operator

    Avijit K. Ganguly🇮🇳 · Manoj K. Jaiswal🇮🇳

    Dimension-five photon $(\gamma )$ scalar $(\varphi )$ interaction terms usually appear in the bosonic sector of unified theories of electromagnetism and gravity. In these theories the three propagation eigenstates are different from the three field eigenstates. The dispersion relation in an external magnetic field shows that, for a non- zero energy $(\omega )$, out of the three propagating eigenstates one has superluminal phase velocity $v_p$. During propagation, another eigenstate undergoes amplification or attenuation, showing signs of an unstable system. The remaining one maintains causality. In this paper, using techniques from optics as well as gravity, we identify the energy $(\omega )$ interval outside which $v_p\le c$ for the field eigenstates $|{\gamma }_{\parallel }>$ and $|\varphi >$, and stability of the system is restored. The behavior of group velocity $v_g$ is also explored in the same context. We conclude by pointing out its possible astrophysical implications.

    hep-phastro-ph.HEPRD(2014)·4 citations
25. 25*

    Color screening masses from string models

    Oleg Andreev🇷🇺

    We use gauge/string duality to estimate the Debye screening mass at non-zero temperature and baryon chemical potential. We interpret this mass as the smallest one in the open string channel. Comparisons are made with the results from holography and lattice QCD.

    hep-phhep-lathep-thnucl-thPRD(2016)·11 citations
26. 26*

    Covariant Spectator Theory of heavy-light and heavy mesons and the predictive power of covariant interaction kernels

    Sofia Leitão🇵🇹 · Alfred Stadler🇵🇹 · M. T. Peña🇵🇹 · Elmar P. Biernat🇵🇹

    The Covariant Spectator Theory (CST) is used to calculate the mass spectrum and vertex functions of heavy-light and heavy mesons in Minkowski space. The covariant kernel contains Lorentz scalar, pseudoscalar, and vector contributions. The numerical calculations are performed in momentum space, where special care is taken to treat the strong singularities present in the confining kernel. The observed meson spectrum is very well reproduced after fitting a small number of model parameters. Remarkably, a fit to a few pseudoscalar meson states only, which are insensitive to spin-orbit and tensor forces and do not allow to separate the spin-spin from the central interaction, leads to essentially the same model parameters as a more general fit. This demonstrates that the covariance of the chosen interaction kernel is responsible for the very accurate prediction of the spin-dependent quark-antiquark interactions.

    hep-phnucl-thPLB(2017)·20 citations
27. 27*

    Nonlinear Breit-Wheeler pair production in a tightly focused laser beam

    A. Di Piazza🇩🇪

    The only available analytical framework for investigating QED processes in a strong laser field systematically relies on approximating the latter as a plane wave. However, realistic high-intensity laser beams feature much more complex space-time structures than plane waves. Here, we show the feasibility of an analytical framework for investigating strong-field QED processes in laser beams of arbitrary space-time structure by determining the energy spectrum of positrons produced via nonlinear Breit-Wheeler pair production as a function of the background field in the realistic assumption that the energy of the incoming photon is the largest dynamical energy in the problem. A numerical evaluation of the angular resolved positron spectrum shows significant quantitative differences with respect to the analogous result in a plane wave, such that the present results will be also important for the design of upcoming strong laser facilities aiming at measuring this process.

    hep-phPRL(2016)·95 citations
28. 28*

    Summary of Structure Functions and PDFs Working Group

    R. McNulty🇮🇪 · R. S. Thorne🇬🇧 · K. Wichmann🇩🇪

    This summary presents personal highlights from the Structure Functions and PDFs Working Group (WG1) at DIS 2016.

    hep-phPoS(2016)·2 citations
29. 29*

    The sigma meson from QCD sum rules for large-$N_c$ Regge spectra

    S.S. Afonin🇷🇺 · T.D. Solomko🇷🇺

    The QCD sum rules in the large-$N_c$ limit for the light non-strange vector, axial and scalar mesons are considered assuming a string-like linear spectrum for the radially excited states. We propose a improved method for combined analysis of these channels that gives a reasonable description of the observed spectrum. In the vector-axial case, fixing the pion decay constant and the gluon condensate we obtain more or less physical values for the masses of ground states and the quark condensate. Thus a typical need for this method to fix the mass of some ground state is overcome. Using in the scalar channel the values of presumably universal slope of radial trajectories and the quark condensate obtained in the vector-axial channel, we find that, in contrast to some strong claims in the literature, a prediction of light scalar state with a mass close to the mass of $f_0(500)$ seems to be natural in the considered approach and may follow in a natural way from the Regge phenomenology.

    hep-phEPJC(2016)·10 citations
30. 30*

    Gradient expansion for anisotropic hydrodynamics

    Wojciech Florkowski🇵🇱 · Radoslaw Ryblewski🇵🇱 · Michał Spaliński🇵🇱

    We compute the gradient expansion for anisotropic hydrodynamics. The results are compared with the corresponding expansion of the underlying kinetic-theory model with the collision term treated in the relaxation time approximation. We find that a recent formulation of anisotropic hydrodynamics based on an anisotropic matching principle yields the first three terms of the gradient expansion in agreement with those obtained for the kinetic theory. This gives further support for this particular hydrodynamic model as a good approximation of the kinetic-theory approach. We further find that the gradient expansion of anisotropic hydrodynamics is an asymptotic series, and the singularities of the analytic continuation of its Borel transform indicate the presence of non-hydrodynamic modes.

    ↳ nucl-thhep-phPRD(2016)·43 citations
31. 31*

    First exploratory calculation of the long-distance contributions to the rare kaon decays $K\to \pi {\ell }^{+}{\ell }^{-}$

    Norman H. Christ🇺🇸 · Xu Feng🇺🇸 · Andreas Juttner🇬🇧 · Andrew Lawson🇬🇧 · Antonin Portelli🇬🇧 · Christopher T. Sachrajda🇬🇧

    The rare decays of a kaon into a pion and a charged lepton/antilepton pair proceed via a flavour changing neutral current and therefore may only be induced beyond tree level in the Standard Model. This natural suppression makes these decays sensitive to the effects of potential New Physics. The CP conserving $K\to \pi {\ell }^{+}{\ell }^{-}$ decay channels however are dominated by a single photon exchange; this involves a sizeable long-distance hadronic contribution which represents the current major source of theoretical uncertainty. Here we outline our methodology for the computation of the long-distance contributions to these rare decay amplitudes using lattice QCD and present the numerical results of the first exploratory studies of these decays in which all but the disconnected diagrams are evaluated. The domain wall fermion ensembles of the RBC and UKQCD collaborations are used, with a pion mass of $M_{\pi }\sim 430\mathrm{MeV}$ and a kaon mass of $M_K\sim 625\mathrm{MeV}$. In particular we determine the form factor, $V(z)$, of the $K^{+}\to {\pi }^{+}{\ell }^{+}{\ell }^{-}$ decay from the lattice at small values of $z=q^2/M_K^2$, obtaining $V(z)=1.37(36),0.68(39),0.96(64)$ for the three values of $z=-0.5594(12),-1.0530(34),-1.4653(82)$ respectively.

    ↳ hep-lathep-phPRD(2016)·64 citations
32. 32*

    New Limits on the Photon Mass with Radio Pulsars in the Magellanic Clouds

    Jun-Jie Wei🇨🇳 · Er-Kang Zhang🇨🇳 · Song-Bo Zhang🇨🇳 · Xue-Feng Wu🇨🇳

    A conservative constraint on the rest mass of the photon can be estimated under the assumption that the frequency dependence of dispersion from astronomical sources is mainly contributed by the nonzero photon mass effect. Photon mass limits have been earlier set through the optical emissions of the Crab Nebula pulsar, but we prove that these limits can be significantly improved with the dispersion measure (DM) measurements of radio pulsars in the Large and Small Magellanic Clouds. The combination of DM measurements of pulsars and distances of the Magellanic Clouds provide a strict upper limit on the photon mass as low as $m_{\gamma }\le 2.0\times 10^{-45}\mathrm{g}$, which is at least four orders of magnitude smaller than the constraint from the Crab Nebula pulsar. Although our limit is not as tight as the current best result ($\sim 10^{-47}\mathrm{g}$) from a fast radio burst (FRB 150418) at a cosmological distance, the cosmological origin of FRB 150418 remains under debate; and our limit can reach the same high precision of FRB 150418 when it has an extragalactic origin ($\sim 10^{-45}\mathrm{g}$).

    ↳ astro-ph.HEastro-ph.COhep-phRes.Astron.Astrophys.(2017)·24 citations
33. 33*

    Supernova Physics at DUNE

    Artur Ankowski🇺🇸 · John Beacom🇺🇸 · Omar Benhar🇮🇹 · Sun Chen🇺🇸 · John Cherry🇺🇸 · Yanou Cui🇺🇸 · Alexander Friedland🇺🇸 · Ines Gil-Botella🇪🇸 · Alireza Haghighat🇺🇸 · Shunsaku Horiuchi🇺🇸 · Patrick Huber🇺🇸 · James Kneller🇺🇸 and 12 other authors

    The DUNE/LBNF program aims to address key questions in neutrino physics and astroparticle physics. Realizing DUNE's potential to reconstruct low-energy particles in the 10-100 MeV energy range will bring significant benefits for all DUNE's science goals. In neutrino physics, low-energy sensitivity will improve neutrino energy reconstruction in the GeV range relevant for the kinematics of DUNE's long-baseline oscillation program. In astroparticle physics, low-energy capabilities will make DUNE's far detectors the world's best apparatus for studying the electron-neutrino flux from a supernova. This will open a new window to unrivaled studies of the dynamics and neutronization of a star's central core in real time, the potential discovery of the neutrino mass hierarchy, provide new sensitivity to physics beyond the Standard Model, and evidence of neutrino quantum-coherence effects. The same capabilities will also provide new sensitivity to `boosted dark matter' models that are not observable in traditional direct dark matter detectors.

    ↳ hep-exastro-ph.HEhep-ph51 citations
34. 34*

    Divergence of the Chapman-Enskog expansion in relativistic kinetic theory

    Gabriel S. Denicol🇧🇷 · Jorge Noronha🇧🇷

    In this letter we show for the first time that the relativistic Chapman-Enskog series for a massless gas undergoing Bjorken expansion diverges. In order to fix this problem, we propose a novel type of expansion that includes non-perturbative contributions in the Knudsen number that are not considered in Chapman-Enskog theory. This approach is in good agreement with exact solutions of the Boltzmann equation for a wide range of values of Knudsen number and does not display the clear signs of divergence exhibited by the Chapman-Enskog series.

    ↳ nucl-thhep-phhep-th98 citations
35. 35*

    Estimating cosmological parameters by the simulated data of gravitational waves from the Einstein Telescope

    Rong-Gen Cai🇨🇳 · Tao Yang🇨🇳

    We investigate the constraint ability of the gravitational wave (GW) as the standard siren on the cosmological parameters by using the third-generation gravitational wave detector: the Einstein Telescope. We simulate the luminosity distances and redshift measurements from 100 to 1000 GW events. We use two different algorithms to constrain the cosmological parameters. For the Hubble constant $H_0$ and dark matter density parameter ${\Omega }_m$, we adopt the Markov chain Monte Carlo approach. We find that with about 500-600 GW events we can constrain the Hubble constant with an accuracy comparable to \textit{Planck} temperature data and \textit{Planck} lensing combined results, while for the dark matter density, GWs alone seem not able to provide the constraints as good as for the Hubble constant; the sensitivity of 1000 GW events is a little lower than that of \textit{Planck} data. It should require more than 1000 events to match the \textit{Planck} sensitivity. Yet, for analyzing the more complex dynamical property of dark energy, i.e., the equation of state $w$, we adopt a new powerful nonparametric method: the Gaussian process. We can reconstruct $w$ directly from the observational luminosity distance at every redshift. In the low redshift region, we find that about 700 GW events can give the constraints of $w(z)$ comparable to the constraints of a constant $w$ by \textit{Planck} data with type Ia supernovae. Those results show that GWs as the standard sirens to probe the cosmological parameters can provide an independent and complementary alternative to current experiments.

    ↳ astro-ph.COgr-qchep-phhep-thPRD(2017)·201 citations
36. 36*

    Lattice QCD calculation of form factors for ${\Lambda }_b\to \Lambda (1520){\ell }^{+}{\ell }^{-}$ decays

    Stefan Meinel🇺🇸 · Gumaro Rendon🇺🇸

    Experimental results for mesonic $b\to s{\mu }^{+}{\mu }^{-}$ decays show a pattern of deviations from Standard-Model predictions, which could be due to new fundamental physics or due to an insufficient understanding of hadronic effects. Additional information on the $b\to s{\mu }^{+}{\mu }^{-}$ transition can be obtained from ${\Lambda }_b$ decays. This was recently done using the process ${\Lambda }_b\to \Lambda {\mu }^{+}{\mu }^{-}$, where the $\Lambda$ is the lightest strange baryon. A further interesting channel is ${\Lambda }_b\to p^{+}{K}^{-}{\mu }^{+}{\mu }^{-}$, where the $p^{+}{K}^{-}$ final state receives contributions from multiple higher-mass $\Lambda$ resonances. The narrowest and most prominent of these is the $\Lambda (1520)$, which has $J^P={\frac{3}{2}}^{-}$. Here we present an ongoing lattice QCD calculation of the relevant ${\Lambda }_b\to \Lambda (1520)$ form factors. We discuss the choice of interpolating field for the $\Lambda (1520)$, and explain our method for extracting the fourteen ${\Lambda }_b\to \Lambda (1520)$ helicity form factors from correlation functions that are computed in the $\Lambda (1520)$ rest frame. We present preliminary numerical results at a pion mass of 340 MeV and a lattice spacing of 0.11 fm. This calculation uses a domain-wall action for the $u$, $d$, and $s$ quarks and a relativistic heavy-quark action for the $b$ quark, and is based on gauge-field configurations generated by the RBC and UKQCD Collaborations.

    ↳ hep-lathep-phPoS(2016)·10 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.