Mon·Sep 7, 2015Monday·September 7, 2015

1. 01*

   Transport coefficients of the Gribov-Zwanziger plasma

   Wojciech Florkowski🇵🇱 · Radoslaw Ryblewski🇵🇱 · Nan Su🇩🇪 · Konrad Tywoniuk🇪🇸

   We study dynamic features of a plasma consisting of gluons whose infrared dynamics is improved by the Gribov-Zwanziger quantization. This approach embodies essential features of color confinement which set the plasma apart from conventional quasiparticle systems in several aspects. Our study focusses on a boost-invariant expansion for in- and out-of-equilibrium settings, which at late times can be characterized by the sound velocity, $c_s$, and the shear, $\eta$, and bulk, $\zeta$, viscosities. We obtain explicit expressions for the transport coefficients $\eta$ and $\zeta$ and check that they are consistent with the numerical solutions of the kinetic equation. At high temperature, keeping both the Gribov parameter and the relaxation time constant, we find a scaling $\zeta /\eta \propto 1/3-c_s^2$ which manifests strong breaking of conformal symmetry in contrast to the case of weakly coupled plasmas.

   hep-phhep-thnucl-thPRC(2016)·57 citations
2. 02*

   Lepton Flavor Non-Universality in B-meson Decays from a U(2) Flavor Model

   Adam Falkowski🇫🇷 · Marco Nardecchia🇬🇧 · Robert Ziegler🇫🇷

   We address the recent anomalies in semi-leptonic $B$-meson decays using a model of fermion masses based on the $U(2)$ flavor symmetry. The new contributions to $b\to s\ell \ell$ transitions arise due to a tree-level exchange of a $Z^{\prime }$ vector boson gauging a $U(1)$ subgroup of the flavor symmetry. They are controlled by a single parameter and are approximately aligned to the Standard Model prediction, with constructive interference in the $e$-channel and destructive interference in the $\mu$-channel. The current experimental data on semi-leptonic $B$-meson decays can be very well reproduced without violating existing constraints from flavor violation in the quark and lepton sectors. Our model will be tested by new measurements of $b\to s\ell \ell$ transitions and also by future electroweak precision tests, direct $Z^{\prime }$ searches, and $\mu$-$e$ conversion in nuclei.

   hep-phJHEP(2015)·164 citations
3. 03*

   Heavy quark potential from QCD-related effective coupling

   Cesar Ayala🇪🇸 · Pedro Gonzalez🇪🇸 · Vicente Vento🇪🇸

   We implement our past investigations in the quark-antiquark interaction through a non-perturbative running coupling defined in terms of a gluon mass function, similar to that used in some Schwinger-Dyson approaches. This coupling leads to a quark-antiquark potential, which satisfies not only asymptotic freedom but also describes linear confinement correctly. From this potential, we calculate the bottomonium and charmonium spectra below the first open flavor meson-meson thresholds and show that for a small range of values of the free parameter determining the gluon mass function an excellent agreement with data is attained.

   hep-phnucl-thJ.Phys.G(2016)·8 citations
4. 04*

   Equilibration of hadrons in HICs via Hagedorn States

   M. Beitel🇩🇪 · K. Gallmeister🇩🇪 · C. Greiner🇩🇪

   Hagedorn states (HS) are a tool to model the hadronization process which occurs in the phase transition region between the quark gluon plasma (QGP) and the hadron resonance gas (HRG). These states are believed to appear near the Hagedorn temperature $T_H$ which in our understanding equals the critical temperature $T_c$. A covariantly formulated bootstrap equation is solved to generate the zoo of these particles characterized baryon number $B$, strangeness $S$ and electric charge $Q$. These hadron-like resonances are characterized by being very massive and by not being limited to quantum numbers of known hadrons. All hadronic properties like masses, spectral functions etc.are taken from the hadronic transport model Ultra Relativistic Quantum Molecular Dynamics (UrQMD). Decay chains of single Hagedorn states provide a well description of experimentally observed multiplicity ratios of strange and multi-strange particles. In addition, the final energy spectra of resulting hadrons show a thermal-like distribution with the characteristic Hagedorn temperature $T_H$. Box calculations including these Hagedorn states are performed. Indeed, the time scales leading to equilibration of the system are drastically reduced down to 2...5 fm/c.

   hep-phJ.Phys.Conf.Ser.(2016)·3 citations
5. 05*

   Electroweak vacuum stability in classically conformal B-L extension of the Standard Model

   Arindam Das🇺🇸 · Nobuchika Okada🇺🇸 · Nathan Papapietro🇺🇸

   We consider the minimal U(1)${}_{B-L}$ extension of the Standard Model (SM) with the classically conformal invariance, where an anomaly free U(1)${}_{B-L}$ gauge symmetry is introduced along with three generations of right-handed neutrinos and a U(1)${}_{B-L}$ Higgs field. Because of the classically conformal symmetry, all dimensional parameters are forbidden. The $B-L$ gauge symmetry is radiatively broken through the Coleman-Weinberg mechanism, generating the mass for the $U(1{)}_{B-L}$ gauge boson ($Z^{\prime }$ boson) and the right-handed neutrinos. Through a small negative coupling between the SM Higgs doublet and the $B-L$ Higgs field, the negative mass term for the SM Higgs doublet is generated and the electroweak symmetry is broken. In this model context, we investigate the electroweak vacuum instability problem in the SM. It is known that in the classically conformal U(1)${}_{B-L}$ extension of the SM, the electroweak vacuum remains unstable in the renormalization group analysis at the one-loop level. In this paper, we extend the analysis to the two-loop level, and perform parameter scans. We identify a parameter region which not only solve the vacuum instability problem, but also satisfy the recent ATLAS and CMS bounds from search for $Z^{\prime }$ boson resonance at the LHC Run-2. Considering self-energy corrections to the SM Higgs doublet through the right-handed neutrinos and the $Z^{\prime }$ boson, we derive the naturalness bound on the model parameters to realize the electroweak scale without fine-tunings.

   hep-phhep-exEPJC(2017)·82 citations
6. 06*

   Probing the Goldstone equivalence theorem in Heavy Weak Doublet Decays

   Bhaskar Dutta🇺🇸 · Yu Gao🇺🇸 · David Sanford🇺🇸 · Joel W. Walker🇺🇸

   This paper investigates the decays from heavy higgsino-like weak-doublets into Z, h bosons and missing particles. When pair-produced at the LHC, the subsequent Z, h to 2l, 2b decays in the doublet decay cascade can yield 4l, 2l 2b, and 4b + MET + jets final states. Mutual observation of any two of these channels would provide information on the the associated doublets' decay branching fractions into a Z or h, thereby probing the Goldstone equivalence relation, shedding additional light on the Higgs sector of beyond the Standard Model theories, and facilitating the discrimination of various contending models, in turn. We compare the Z/h decay ratio expected in the Minimal Supersymmetric model, the Next-to Minimal Supersymmetric model and a minimal singlet-doublet dark matter model. Additionally, we conduct a full Monte Carlo analysis of the prospects for detecting the targeted final states during 14 TeV running of the LHC in the context of a representative NMSSM benchmark model.

   hep-phhep-exPRD(2016)·0 citations
7. 07*

   Quarkonia and heavy-light mesons in a covariant quark model

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

   Preliminary calculations using the Covariant Spectator Theory (CST) employed a scalar linear confining interaction and an additional constant vector potential to compute the mesonic mass spectra. In this work we generalize the confining interaction to include more general structures, in particular a vector and also a pseudoscalar part, as suggested by a recent study. A one-gluon-exchange kernel is also implemented to describe the short-range part of the interaction. We solve the simplest CST approximation to the complete Bethe-Salpeter equation, the one-channel spectator equation, using a numerical technique that eliminates all singularities from the kernel. The parameters of the model are determined through a fit to the experimental pseudoscalar meson spectra, with a good agreement for both quarkonia and heavy-light states.

   hep-phEPJ Web Conf.(2016)·2 citations
8. 08*

   Obstacles to extending R-parity violation to Supersymmetric SU(5)

   Najimuddin Khan🇮🇳 · Subhendu Rakshit🇮🇳 · Amitava Raychaudhuri🇮🇳

   We explore the consequences of promoting bilinear R-parity violation, usually formulated in the minimal supersymmetric standard model framework, to a supersymmetric SU(5) grand unified theory. We observe that the limits on proton decay and neutrino mass place tight constraints on the bilinear SU(5) R-parity violating parameters creating a different doublet-triplet issue which cannot be resolved by an extension of the usual fine-tuning in the symmetry breaking scalar sector. If the parameters are made to satisfy the constraints, albeit unnaturally, there remains no room for the possibility to correct the SU(5) fermion mass ratios by introducing R-parity violation.

   hep-ph0 citations
9. 09*

   Preserving Local Gauge Invariance with t-Channel Regge Exchange

   Helmut Haberzettl🇺🇸 · Xiao-Yun Wang🇨🇳 · Jun He🇨🇳

   Considering single-meson photo- and electroproduction off a baryon, it is shown how to restore local gauge invariance that was broken by replacing standard Feynman-type meson exchange in the t-channel by exchange of a Regge trajectory. This is achieved by constructing a contact current whose four-divergence cancels the gauge-invariance-violating contributions resulting from all states above the base state on the Regge trajectory. To illustrate the procedure, modifications necessary for the process $\gamma +p\to K^{+}+{\Sigma }^{\ast 0}$ are discussed in some detail. We also provide the general expression for the contact current for an arbitrary reaction.

   hep-phnucl-thPRC(2015)·24 citations
10. 10*

    Non-Hermitian extension of gauge theories and implications for neutrino physics

    Jean Alexandre🇬🇧 · Carl M. Bender🇬🇧 · Peter Millington🇩🇪

    An extension of QED is considered in which the Dirac fermion has both Hermitian and anti-Hermitian mass terms, as well as both vector and axial-vector couplings to the gauge field. Gauge invariance is restored when the Hermitian and anti-Hermitian masses are of equal magnitude, and the theory reduces to that of a single massless Weyl fermion. An analogous non-Hermitian Yukawa theory is considered, and it is shown that this model can explain the smallness of the light-neutrino masses and provide an additional source of leptonic CP violation.

    ↳ hep-thhep-phmath-phmath.MPJHEP(2015)·70 citations
11. 11*

    Non-local gravity in D-dimensions: Propagator, entropy and bouncing Cosmology

    Aindriu Conroy🇬🇧 · Anupam Mazumdar🇬🇧 · Spyridon Talaganis🇬🇧 · Ali Teimouri🇬🇧

    We present the graviton propagator for an infinite derivative, $D$-dimensional, non-local action, up to quadratic order in curvature around a Minkowski background, and discuss the conditions required for this class of gravity theory to be ghost-free. We then study the gravitational entropy for de-Sitter and Anti-de Sitter backgrounds, before comparing with a recently derived result for a Schwarzschild blackhole, generalised to arbitrary $D$-dimensions, whereby the entropy is given simply by the area law. A novel approach of decomposing the entropy into its $(r,t)$ and spherical components is adopted in order to illustrate the differences more clearly. We conclude with a discussion of de-Sitter entropy in the framework of a non-singular bouncing cosmology.

    ↳ hep-thastro-ph.COgr-qchep-phPRD(2015)·41 citations
12. 12*

    $A_{LL}(p_T)$ for single hadron photoproduction at high $p_T$

    Maxime Levillain🇫🇷

    In order to understand the gluon contribution to the nucleon spin, some experiments can study the production of hadrons at high transverse momemtum from lepton-nucleon or nucleon-nucleon scattering. RHIC has recently measured such double spin asymmetries $A_{LL}(p_T)$ for pion production at high center of mass energies, and inclusion of its data to global fits based on NLO collinear pQCD calculations gives some constraints on the gluon polarization in the range $0.05<x_g<0.2$. To complement these results at COMPASS range, we will present preliminary COMPASS results on double longitudinal spin asymmetries $A_{LL}(p_T)$ for single hadron production measured on deuteron and proton target at $Q^2<1$ GeV${}^2$, $p_T>1$ GeV/c and center of mass energy $\sqrt{s}\approx 18$ GeV. All COMPASS data taken from 2002 to 2011 by scattering 160 GeV polarized muons on longitudinally polarized ${}^6$LiD and NH${}_3$ targets have been used, and the number of hadrons collected with $p_T>1$ GeV/c for this analysis amounts to about 10 millions. The obtained asymmetries will be compared to theoretical predictions of at NLO without gluon resummation calculation.

    ↳ hep-exhep-ph2 citations
13. 13*

    Supersymmetry and Inflation

    S. Ferrara🇨🇭 · A. Sagnotti🇮🇹

    Theories with elementary scalar degrees of freedom seem nowadays required for simple descriptions of the Standard Model and of the Early Universe. It is then natural to embed theories of inflation in supergravity, also in view of their possible ultraviolet completion in String Theory. After some general remarks on inflation in supergravity, we describe examples of minimal inflaton dynamics which are compatible with recent observations, including higher-curvature ones inspired by the Starobinsky model. We also discuss different scenarios for supersymmetry breaking during and after inflation, which include a revived role for non-linear realizations. In this spirit, we conclude with a discussion of the link, in four dimensions, between "brane supersymmetry breaking" and the super--Higgs effect in supergravity.

    ↳ hep-thastro-ph.COhep-phInt.J.Mod.Phys.(2017)·29 citations
14. 14*

    Principal component analysis of the reionization history from Planck 2015 data

    Wei-Ming Dai🇨🇳 · Zong-Kuan Guo🇨🇳 · Rong-Gen Cai🇨🇳

    The simple assumption of an instantaneous reionization of the Universe may bias estimates of cosmological parameters. In this paper a model-independent principal component method for the reionization history is applied to give constraints on the cosmological parameters from recent Planck 2015 data. We find that the Universe are not completely reionized at redshifts $z\ge 8.5$ at 95% CL. Both the reionization optical depth and the matter fluctuation amplitude are higher than but consistent with those obtained in the standard instantaneous reionization scheme. The high estimated value of the matter fluctuation amplitude strengthens the tension between Planck CMB observations and some astrophysical data, such as cluster counts and weak lensing. The tension can significantly be relieved if the neutrino masses are allowed to vary. Thanks to a high scalar spectral index, the low-scale spontaneously broken SUSY inflationary model can fit the data well, which is marginally disfavored at 95% CL in the Planck analysis.

    ↳ astro-ph.COhep-phPRD(2015)·7 citations
15. 15*

    Neutrino flavor instabilities in a time-dependent supernova model

    Sajad Abbar🇺🇸 · Huaiyu Duan (UNM)🇺🇸

    A dense neutrino medium such as that inside a core-collapse supernova can experience collective flavor conversion or oscillations because of the neutral-current weak interaction among the neutrinos. This phenomenon has been studied in a restricted, stationary supernova model which possesses the (spatial) spherical symmetry about the center of the supernova and the (directional) axial symmetry around the radial direction. Recently it has been shown that these spatial and directional symmetries can be broken spontaneously by collective neutrino oscillations. In this paper we analyze the neutrino flavor instabilities in a time-dependent supernova model. Our results show that collective neutrino oscillations start at approximately the same radius in both the stationary and time-dependent supernova models unless there exist very rapid variations in local physical conditions on timescales of a few microseconds or shorter. Our results also suggest that collective neutrino oscillations can vary rapidly with time in the regimes where they do occur which need to be studied in time-dependent supernova models.

    ↳ astro-ph.HEhep-phnucl-thPLB(2015)·72 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.