Thu·Sep 24, 2015Thursday·September 24, 2015

1. 01*

   QCD corrections to ZZ production in gluon fusion at the LHC

   Fabrizio Caola🇨🇭 · Kirill Melnikov🇩🇪 · Raoul Röntsch🇺🇸 · Lorenzo Tancredi🇩🇪

   We compute the next-to-leading order QCD corrections to the production of two Z-bosons in the annihilation of two gluons at the LHC. Being enhanced by a large gluon flux, these corrections provide distinct and, potentially, the dominant part of the N${}^3$LO QCD contributions to Z-pair production in proton collisions. The $gg\to ZZ$ annihilation is a loop-induced process that receives the dominant contribution from loops of five light quarks, that are included in our computation in the massless approximation. We find that QCD corrections increase the $gg\to ZZ$ production cross section by $\mathcal{O}(50\%-100\%)$ depending on the values of the renormalization and factorization scales used in the leading order computation, and the collider energy. The large corrections to $gg\to ZZ$ channel increase the $pp\to ZZ$ cross section by about six to eight percent, exceeding the estimated theoretical uncertainty of the recent NNLO QCD calculation.

   hep-phhep-exPRD(2015)·240 citations
2. 02*

   The production of photons in relativistic heavy-ion collisions

   Jean-François Paquet🇨🇦 · Chun Shen🇨🇦 · Gabriel S. Denicol🇨🇦 · Matthew Luzum🇧🇷 · Björn Schenke🇺🇸 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦

   In this work it is shown that the use of a hydrodynamical model of heavy ion collisions which incorporates recent developments, together with updated photon emission rates greatly improves agreement with both ALICE and PHENIX measurements of direct photons, supporting the idea that thermal photons are the dominant source of direct photon momentum anisotropy. The event-by-event hydrodynamical model uses IP-Glasma initial states and includes, for the first time, both shear and bulk viscosities, along with second order couplings between the two viscosities. The effect of both shear and bulk viscosities on the photon rates is studied, and those transport coefficients are shown to have measurable consequences on the photon momentum anisotropy.

   hep-phnucl-exnucl-thPRC(2016)·442 citations
3. 03*

   Galaxy Cluster Thermal X-Ray Spectra Constrain Axion-Like Particles

   Joseph P. Conlon🇬🇧 · M. C. David Marsh🇬🇧 · Andrew J. Powell🇬🇧

   Axion-like particles (ALPs) and photons inter-convert in the presence of a magnetic field. At keV energies in the environment of galaxy clusters, the conversion probability can become unsuppressed for light ALPs. Conversion of thermal X-ray photons into ALPs can introduce a step-like feature into the cluster thermal bremsstrahlung spectrum, and we argue that existing X-ray data on galaxy clusters should be sufficient to extend bounds on ALPs in the low-mass region $m_a\lesssim 1\times 10^{-12}\mathrm{eV}$ down to $M\sim 7\times 10^{11}\mathrm{GeV}$, and that for $10^{11}\mathrm{GeV}<M\lesssim 10^{12}$ GeV light ALPs give rise to interesting and unique observational signatures that may be probed by existing and upcoming X-ray (and potentially X-ray polarisation) observations of galaxy clusters.

   hep-phastro-ph.COastro-ph.HEPRD(2016)·39 citations
4. 04*

   Dark photons from charm mesons at LHCb

   Philip Ilten🇺🇸 · Jesse Thaler🇺🇸 · Mike Williams🇺🇸 · Wei Xue🇺🇸

   We propose a search for dark photons $A^{\prime }$ at the LHCb experiment using the charm meson decay $D^{\ast }(2007{)}^0\to D^0{A}^{\prime }$. At nominal luminosity, $D^{\ast 0}\to D^0\gamma$ decays will be produced at about 700kHz within the LHCb acceptance, yielding over 5 trillion such decays during Run 3 of the LHC. Replacing the photon with a kinetically-mixed dark photon, LHCb is then sensitive to dark photons that decay as $A^{\prime }\to e^{+}{e}^{-}$. We pursue two search strategies in this paper. The displaced strategy takes advantage of the large Lorentz boost of the dark photon and the excellent vertex resolution of LHCb, yielding a nearly background-free search when the $A^{\prime }$ decay vertex is significantly displaced from the proton-proton primary vertex. The resonant strategy takes advantage of the large event rate for $D^{\ast 0}\to D^0{A}^{\prime }$ and the excellent invariant mass resolution of LHCb, yielding a background-limited search that nevertheless covers a significant portion of the $A^{\prime }$ parameter space. Both search strategies rely on the planned upgrade to a triggerless-readout system at LHCb in Run 3, which will permit identification of low-momentum electron-positron pairs online during data taking. For dark photon masses below about 100MeV, LHCb can explore nearly all of the dark photon parameter space between existing prompt-$A^{\prime }$ and beam-dump limits.

   hep-phhep-exPRD(2015)·195 citations
5. 05*

   Multi-field inflation and the field-space metric

   Joshua Erlich🇺🇸 · Jackson Olsen🇺🇸 · Zhen Wang🇺🇸

   Multi-field inflation models include a variety of scenarios for how inflation proceeds and ends. Models with the same potential but different kinetic terms are common in the literature. We compare spiral inflation and Dante's inferno-type models, which differ only in their field-space metric. We justify a single-field effective description in these models and relate the single-field description to a mass-matrix formalism. We note the effects of the nontrivial field-space metric on inflationary observables, and consequently on the viability of these models. We also note a duality between spiral inflation and Dante's inferno models with different potentials.

   hep-phJCAP(2016)·5 citations
6. 06*

   Constraints on extra dimensions from atomic spectroscopy

   F. Dahia🇧🇷 · A. S. Lemos🇧🇷

   We consider a hydrogen atom confined in a thick brane embedded in a higher-dimensional space. Due to effects of the extra dimensions, the gravitational potential is amplified in distances smaller than the size of the supplementary space, in comparison with the Newtonian potential. Studying the influence of the gravitational interaction modified by the extra dimensions on the energy levels of the hydrogen atom, we find independent constraints for the higher-dimensional Planck mass in terms of the thickness of the brane by using accurate measurements of atomic transition frequencies. The constraints are very stringent for narrow branes.

   hep-phgr-qchep-thphysics.atom-ph+1PRD(2016)·23 citations
7. 07*

   The Diboson Excesses in Leptophobic $U(1{)}_{\mathrm{LP}}$ Models from String Theories

   Tianjun Li🇨🇳 · James A. Maxin🇺🇸 · Van E. Mayes🇺🇸 · Dimitri V. Nanopoulos🇺🇸

   The ATLAS Collaboration has reported excesses in the search for resonant diboson production with decay modes to hadronic final states at a diboson invariant mass around 2 TeV in boosted jets from $WZ$, $W^{+}{W}^{-}$, and $ZZ$ channels. Given potential contamination, we investigate the anomalies in leptophobic $U(1{)}_{\mathrm{LP}}$ models. We show that leptophobic models can be constructed in flipped $SU(5)\times U(1{)}_X$ models from free fermionic string constructions and Pati-Salam models from D-brane constructions. Additionally, we perform a collider phenomenological analysis to study production cross sections for $pp\to Z^{\prime }\to jj/t\bar{t}/WW/Zh$ and discover the excess can be interpreted in both the leptophobic flipped $SU(5)\times U(1{)}_X$ models and intersecting D-branes.

   hep-phhep-exPRD(2016)·18 citations
8. 08*

   Hyperon polarization from the twist-3 distribution in the unpolarized proton-proton collision

   Yuji Koike (Niigata U)🇯🇵 · Kenta Yabe (Niigata U)🇯🇵 · Shinsuke Yoshida (Niigata U)🇯🇵

   We investigate the transverse polarization of a hyperon produced in the high-energy unpolarized proton-proton collision, $pp\to {\Lambda }^{\uparrow }X$, based on the collinear twist-3 factorization formalism. We focus on the contribution from the twist-3 distribution in one of the unpolarized proton and the transversity fragmentation function for the final hyperon. Utilizing the "master formula" for the soft-gluon-pole cross section, we clarify the reason for why it receives only the derivative term of the twist-3 distribution. We also present the first computation of the soft-fermion-pole cross section and found that it vanishes. This means that the derivative of the soft-gluon-pole function is the only source for the twist-3 cross section from the unpolarized twist-3 distribution, which provides a useful basis for a phenomenological analysis.

   hep-phPRD(2015)·23 citations
9. 09*

   Aspects of Meson Condensation

   Andrea Mammarella🇮🇹

   In this work pion and kaon condensation in the framework of chiral perturbation theory is studied. I consider a system at vanishing temperature with nonzero isospin chemical potential and strangeness chemical potential; meson masses and mixing in the normal phase, the pion condensation phase and the kaon condensation phase are described. There are differences with previous works, but the results presented here are supported by both theory group analysis and by direct calculations. Some pion decay channels in the normal and the pion condensation phases are studied, finding a nonmonotonic behavior of the $\Gamma$ decay width as a function of ${\mu }_I$.

   hep-phEPJ Web Conf.(2016)·2 citations
10. 10*

    A modified Friedberg-Lee symmetry for the TM1 neutrino mixing

    Zhen-hua Zhao🇨🇳

    In this letter, we put forward a special neutrino mass matrix which is invariant under a modified Friedberg-Lee (FL) transformation ${\nu }_e^{}\to {\nu }_e^{}-2\theta$ and ${\nu }_{\mu ,\tau }^{}\to {\nu }_{\mu ,\tau }^{}+\theta$ with $\theta$ being a space-time independent element of the Grassmann algebra. Compared to the original FL symmetry (with the transformation ${\nu }_{e,\mu ,\tau }^{}\to {\nu }_{e,\mu ,\tau }^{}+\theta$) which results in the TM2 neutrino mixing, the modified FL symmetry will lead us to the TM1 mixing which has a better agreement with the experimental results. While the original FL symmetry has to be broken in order to produce a realistic neutrino mass spectrum, the modified FL symmetry is allowed to remain intact and give us a vanishing $m_1^{}$. A combination of the FL symmetry with the $\mu$-$\tau$ reflection symmetry is also discussed.

    hep-phPRD(2015)·11 citations
11. 11*

    Chiral Lagrangian and chiral quark model from confinement in QCD

    Yu. A. Simonov (State Research Center, Institute of Theoretical and Experimental Physics)🇷🇺

    The effective chiral Lagrangian in both nonlocal form $L_{ECCL}$ and standard local form $L_{ECL}$ are derived in QCD using the confining kernel, obtained in the vacuum correlator formalism. As a result all coefficients of $L_{ECL}$ can be computed via $q\bar{q}$ Green's functions. In the $p^2$ order of $L_{ECL}$ one obtains GOR relations and quark decay constants $f_a$ are calculated $a=1,...8$, while in the $p^4$ order the coefficients $L_1,L_2,L_3,L_4,L_5,L_6$ are obtained in good agreement with the values given by data. The chiral quark model is shown to be a simple consequence of $L_{ECCL}$ with defined coefficients. It is demonstrated that $L_{ECCL}$ gives an extension of the limiting low-energy Lagrangian $L_{ECL}$ to arbitrary momenta.

    hep-phInt.J.Mod.Phys.A(2016)·17 citations
12. 12*

    The B -> pi tau nu decay in the context of the 2HDM type II

    Florian U. Bernlochner🇩🇪

    In this manuscript the B -> pi tau nu decay is investigated in the context of the 2HDM type II extension of the SM. In particular, predictions for the ratio of semileptonic branching fractions from l = tau and l = electron, muon are produced and an exclusion based on the MSSM parameters tan beta and mH+ from a preliminary Belle measurement are reported. An alternative variable to the ratio of branching fractions that could offer increased sensitivity is discussed that could result in increased sensitivity to rule out contributions from additional scalar mediators.

    hep-phhep-exPRD(2015)·34 citations
13. 13*

    Magnetically induced QCD Kondo effect

    Sho Ozaki🇯🇵 · Kazunori Itakura🇯🇵 · Yoshio Kuramoto🇯🇵

    The "QCD Kondo effect" stems from the color exchange interaction in QCD with non-Abelian property, and can be realized in a high-density quark matter containing heavy-quark impurities. We propose a novel type of the QCD Kondo effect induced by a strong magnetic field. In addition to the fact that the magnetic field does not affect the color degrees of freedom, two properties caused by the Landau quantization in a strong magnetic field are essential for the "magnetically induced QCD Kondo effect"; (1) dimensional reduction to 1+1-dimensions, and (2) finiteness of the density of states for lowest energy quarks. We demonstrate that, in a strong magnetic field $B$, the scattering amplitude of a massless quark off a heavy quark impurity indeed shows a characteristic behavior of the Kondo effect. The resulting Kondo scale is estimated as ${\Lambda }_{\mathrm{K}}\simeq \sqrt{e_{q}B}{\alpha }_s^{1/3}\exp \{-4\pi /N_c{\alpha }_s\log (4\pi /{\alpha }_s)\}$ where ${\alpha }_s$ and $N_c$ are the fine structure constant of strong interaction and the number of colors in QCD, and $e_q$ is the electric charge of light quarks.

    hep-phcond-mat.str-elhep-latnucl-thPRD(2016)·39 citations
14. 14*

    Origin of a large CP asymmetry in B+- --> K+ K- K+ decays

    Leonard Lesniak🇵🇱 · Piotr Zenczykowski🇵🇱

    Large $CP$-violating asymmetry effects in the B+- --> K+ K- K decays have been predicted in the QCD factorization model. The model includes strong K+ K- final-state long-distance interactions in the S-, P-, and also (in the recent analysis) D- wave two-body states. The S-wave two-body unitarity conditions involve interchannel couplings of the kaon-kaon states with the intermediate states of two pions and four pions. As a result, the pion-pion to kaon-kaon rescattering effects are included in the model. It is shown how the weak phase differences together with the existence of two different strong phases of the S-wave decay amplitudes (related to the phases of the kaon scalar strange and non-strange form factors) contribute to the CP-asymmetry in question. The theoretical results are compared with recent experimental data of the LHCb and BABAR Collaborations.

    hep-phhep-exPoS(2015)·0 citations
15. 15*

    Covariant ChPT calculation of the hyperon forward spin polarizability

    Astrid Hiller Blin🇪🇸 · Thomas Gutsche🇩🇪 · Tim Ledwig🇪🇸 · Valery E. Lyubovitskij🇩🇪

    We predict the values for baryon forward spin polarizabilities in fully covariant ChPT and including the virtual contributions of the spin-3/2 states. As the nucleon results are in good agreement with the experimental data and they do not depend on renormalization schemes, we extend the calculations to the hyperon sector.

    hep-phPoS(2016)·0 citations
16. 16*

    Medium modification of hadron masses and the thermodynamics of hadron resonance gas model

    Guru Prakash Kadam🇮🇳 · Hiranmaya Mishra🇮🇳

    We study the effect of temperature (T) and baryon density ({\mu}) dependent hadron masses on the thermodynamics of hadronic matter. We use linear scaling rule in terms of constituent quark masses for all hadrons except for light mesons. T and {\mu} dependent constituent quark masses and the light mesons masses are computed using 2+1 flavor Nambu-Jona-Lasinio (NJL) model. We compute the thermodynamical quantities of hadronic matter within excluded volume hadron resonance gas model (EHRG) with these T and {\mu} dependent hadron masses. We confront the thermodynamical quantities with the lattice quantum chromodynamics (LQCD) at {\mu} = 0 GeV. Further, we comment on the effect of T and {\mu} dependent hadron masses on the transport properties near the transition temperature.

    hep-phPRC(2016)·33 citations
17. 17*

    Flavor dependence of jet quenching in $pp$ collisions and its effect on the $R_{AA}$ for heavy mesons

    B. G. Zakharov🇷🇺

    We study the flavor dependence of the medium modification factor $R_{pp}$ for $pp$ collisions for scenario with formation of a small-size quark-gluon plasma (QGP) for RHIC ($\sqrt{s}=0.2$ TeV) and LHC ($\sqrt{s}=2.76$ TeV) energies. We find that at $p_T\sim 10$ GeV the pion spectrum is suppressed by $\sim 20-30(25-35)$\% for RHIC (LHC), for $D$~($B$) mesons the suppression effect is smaller by a factor of $\sim 0.7-0.8$ ($0.5$). The flavor hierarchy $R_{pp}^{\pi }<R_{pp}^D<R_{pp}^B$ is held at $p_T\lesssim 20$ GeV for RHIC and at $p_T\lesssim 70$ GeV for LHC. This gives a sizeable reduction of the heavy-to-light ratios of the nuclear modification factors $R_{AA}$ as compared to that in the standard scenario without the QGP production in $pp$ collisions.

    hep-phJETP Lett.(2016)·7 citations
18. 18*

    MSSM Dark Matter in Light of Higgs and LUX Results

    W. Abdallah🇪🇬 · S. Khalil🇪🇬

    The constraints imposed on the Minimal Supersymmetric Standard Model (MSSM) parameter space by the Large Hadron Collider (LHC) Higgs mass limit and gluino mass lower bound are revisited. We also analyze the thermal relic abundance of lightest neutralino, which is the Lightest Supersymmetric Particle (LSP). We show that the combined LHC and relic abundance constraints rule out most of the MSSM parameter space except a very narrow region with very large $\tan \beta (\sim 50)$. Within this region, we emphasize that the spin-independent scattering cross section of the LSP with a proton is less than the latest Large Underground Xenon (LUX) limit by at least two order of magnitudes. Finally, we argue that non-thermal Dark Matter (DM) scenario may relax the constraints imposed on the MSSM parameter space. Namely, the following regions are obtained: $m_0\simeq \mathcal{O}(4)$ TeV and $m_{1/2}\simeq 600$ GeV for low $\tan \beta (\sim 10)$; $m_0\sim m_{1/2}\simeq \mathcal{O}(1)$ TeV or $m_0\simeq \mathcal{O}(4)$ TeV and $m_{1/2}\simeq 700$ GeV for large $\tan \beta (\sim 50)$.

    hep-phAdv.High Energy Phys.(2016)·13 citations
19. 19*

    Growth index of matter perturbations in running vacuum models

    Spyros Basilakos🇬🇷 · Joan Solà🇪🇸

    We derive for the first time the growth index of matter perturbations of the FLRW flat cosmological models in which the vacuum energy depends on redshift. A particularly well motivated model of this type is the so-called quantum field vacuum, in which apart from a leading constant term ${\Lambda }_0$ there is also a $H^2$-dependence in the functional form of vacuum, namely $\Lambda (H)={\Lambda }_0+3\nu (H^2-H_0^2)$. Since $|\nu |\ll 1$ this form endows the vacuum energy of a mild dynamics which affects the evolution of the main cosmological observables at the background and perturbation levels. Specifically, at the perturbation level we find that the growth index of the running vacuum cosmological model is ${\gamma }_{{\Lambda }_H}\approx \frac{6+3\nu }{11-12\nu }$ and thus it nicely extends analytically the result of the $\Lambda$CDM model, ${\gamma }_{\Lambda }\approx 6/11$.

    ↳ astro-ph.COgr-qchep-phhep-thPRD(2015)·36 citations
20. 20*

    Chiral separation and chiral magnetic effects in a slab: The role of boundaries

    E. V. Gorbar🇺🇦 · V. A. Miransky🇨🇦 · I. A. Shovkovy🇺🇸 · P. O. Sukhachov🇺🇦

    We study the chiral separation and chiral magnetic effects in a slab of Dirac semimetal of finite thickness, placed in a constant magnetic field perpendicular to its surfaces. We utilize the Bogolyubov boundary conditions with a large Dirac mass (band gap) outside the slab. We find that, in a finite thickness slab, the axial current density is induced by helicity-correlated standing waves and, as a consequence, is quantized. The quantization is seen in its stepped-shape dependence on the fermion chemical potential and a sawtooth-shape dependence on the thickness of the slab. In contrast to a naive expectation, there is no chiral charge accumulation anywhere in the bulk or at the boundaries of the semimetal. In the same slab geometry, we also find that a nonzero chiral chemical potential induces no electric current, as might have been expected from the chiral magnetic effect. We argue that this outcome is natural and points to the truly non-static nature of the latter. By taking into account a nonzero electric field of a double layer near the boundaries of the slab, we find that the low-energy modes under consideration satisfy the continuity equation for axial current density without the anomalous term.

    ↳ cond-mat.mes-hallhep-phhep-thPRB(2015)·28 citations
21. 21*

    Leptonic Decays of Charm

    Simon Eidelman🇷🇺

    We present results of various searches for leptonic decays of charm mesons performed with the Belle detector. Also discussed are $D^0\to \gamma \gamma$ decays.

    ↳ hep-exhep-ph1 citation
22. 22*

    Study of the XYZ states at the BESIII

    Chang-Zheng Yuan (for the BESIII Collaboration)🇨🇳

    With its unique data samples at energies of 3.8--4.6 GeV, the BESIII experiment made a significant contribution to the study of charmonium and charmonium-like states, i.e., the XYZ states. We review the results for observations of the Zc(3900) and Zc(4020) states, the X(3872) in e+e- annihilation, and charmonium psi(1^3D_2) state, as well as measurements of the cross-sections of omega chi_cJ and eta J/psi, and the search for e+e- to gamma chi_cJ and gamma Y(4140). We also present data from BESIII that may further strengthen the study of the XYZ and conventional charmonium states, and discuss perspectives on future experiments.

    ↳ hep-exhep-phFront.Phys.(Beijing)(2015)·31 citations
23. 23*

    Baryon stopping signal for mixed phase formation in HIC

    Yu. B. Ivanov🇷🇺

    It is argued that an irregularity in the baryon stopping is a natural consequence of onset of deconfinement occurring in the compression stage of a nuclear collision. It is an effect of the softest point inherent in an equation of state (EoS) with a deconfinement transition. In order to illustrate this effect, calculations within the three-fluid model were performed with three different EoS's: a purely hadronic EoS, an EoS with a first-order phase transition and that with a smooth crossover transition.

    ↳ nucl-thhep-phJ.Phys.Conf.Ser.(2016)·5 citations
24. 24*

    Dynamical Gap Generation in Topological Insulators

    Paolo Cea🇮🇹

    We developed a quantum field theoretical description for the surface states of three-dimensional topological insulators. Within the relativistic quantum field theory formulation, we investigated the dynamics of low-lying surface states in an applied transverse magnetic field. We argued that, by taking into account quantum fluctuations, in three-dimensional topological insulators there is dynamical generation of a gap by a rearrangement of the Dirac sea. By comparing with available experimental data we found that our theoretical results allowed a consistent and coherent description of the Landau level spectrum of the surface low-lying excitations. Finally, we showed that the recently detected zero-Hall plateau at the charge neutral point could be accounted for by chiral edge states residing at the magnetic domain boundaries between the top and bottom surfaces of the three-dimensional topological insulator.

    ↳ cond-mat.mes-hallcond-mat.otherhep-phhep-thEur.Phys.J.B(2016)·1 citation

* 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.