Thu·Mar 10, 2016Thursday·March 10, 2016

1. 01*

   Constraints on cosmological viscosity and self interacting dark matter from gravitational wave observations

   Gaurav Goswami🇮🇳 · Girish Kumar Chakravarty🇮🇳 · Subhendra Mohanty🇮🇳 · A. R. Prasanna🇮🇳

   It has been shown that gravitational waves propagate through ideal fluids without experiencing any dispersion or dissipation. However, if the medium has a non-zero shear viscosity $\eta$ , gravitational waves will be dissipated at a rate proportional to $G\eta$. We constrain dark matter and dark energy models with non-zero shear viscosity by calculating the dissipation of gravitational waves from GW150914 which propagate over a distance of $410$ Mpc through the dissipative fluid and comparing the data with the theoretical prediction. This provides a proof-of-principle demonstration of the fact that future observations gravitational waves at LIGO have the potential of better constraining the viscosity of dark matter and dark energy.

   hep-phastro-ph.COgr-qcPRD(2017)·45 citations
2. 02*

   LHC Benchmarks from Flavored Gauge Mediation

   N. Ierushalmi🇮🇱 · S. Iwamoto🇮🇱 · G. Lee🇮🇱 · V. Nepomnyashy🇮🇱 · Y. Shadmi🇮🇱

   We present benchmark points for LHC searches from flavored gauge mediation models, in which messenger-matter couplings give flavor-dependent squark masses. Our examples include spectra in which a single squark - stop, scharm, or sup - is much lighter than all other colored superpartners, motivating improved quark flavor tagging at the LHC. Many examples feature flavor mixing; in particular, large stop-scharm mixing is possible. The correct Higgs mass is obtained in some examples by virtue of the large stop A-term. We also revisit the general flavor and CP structure of the models. Even though the A-terms can be substantial, their contributions to EDM's are very suppressed, because of the particular dependence of the A-terms on the messenger coupling. This holds regardless of the messenger-coupling texture. More generally, the special structure of the soft terms often leads to stronger suppression of flavor- and CP-violating processes, compared to naive estimates.

   hep-phhep-exJHEP(2016)·12 citations
3. 03*

   Predictions for diphoton production at the LHC through NNLO in QCD

   John M. Campbell🇺🇸 · R. Keith Ellis🇬🇧 · Ye Li🇺🇸 · Ciaran Williams🇺🇸

   In this paper we present a next-to-next-to-leading order (NNLO) calculation of the process $pp\to \gamma \gamma$ that we have implemented into the parton level Monte Carlo code MCFM. We do not find agreement with the previous calculation of this process in the literature. In addition to the $\mathcal{O}({\alpha }_s^2)$ corrections present at NNLO, we include some effects arising at $\mathcal{O}({\alpha }_s^3)$, namely those associated with gluon-initiated closed fermion loops. We investigate the role of this process in the context of studies of QCD at colliders and as a background for searches for new physics, paying particular attention to the diphoton invariant mass spectrum. We demonstrate that the NNLO QCD prediction for the shape of this spectrum agrees well with functional forms used in recent data-driven fits.

   hep-phhep-exJHEP(2016)·159 citations
4. 04*

   Vacuum Stability of a General Scalar Potential of a Few Fields

   Kristjan Kannike🇪🇪

   We find analytical vacuum stability or bounded below conditions for general scalar potentials of a few fields. After a brief review of copositivity we go beyond it. We discuss the vacuum stability conditions of the general potential of two real scalars, without and with the Higgs boson included in the potential. As further examples, we give explicit vacuum stability conditions for the two Higgs doublet model with no explicit CP breaking, and for the ${\mathbb{Z}}_3$ scalar dark matter with an inert doublet and a complex singlet. We give a short overview of positivity conditions for tensors of quartic couplings via tensor eigenvalues. A Mathematica notebook with the conditions is included with the source files.

   hep-phEPJC(2016)·131 citations
5. 05*

   Exploring $X(5568)$ as a meson molecule

   S. S. Agaev🇦🇿 · K. Azizi🇹🇷 · H. Sundu🇹🇷

   The parameters, i.e. the mass and current coupling of the exotic $X(5568)$ state observed by the D0 Collaboration as well as the decay width of the process $X\to B_s^0{\pi }^{+}$ are explored using $B\bar{K}$ molecule assumption on its structure. Employed computational methods include QCD two-point and light-cone sum rules, latter being considered in the soft-meson approximation. The obtained results are compared with the data of the D0 Collaboration as well as with the predictions of the diquark-antidiquark model. This comparison strengthens a diquark-antidiquark picture for the $X(5568)$ state rather than a meson molecule structure.

   hep-phhep-exhep-latnucl-thEur.Phys.J.Plus(2016)·51 citations
6. 06*

   The leptonic CP phase is determined by an equation involving the PMNS matrix elements

   Hong-Wei Ke🇨🇳 · Jia-Hui Zhou · Xue-Qian Li🇨🇳

   Several approximate equalities among the matrix elements of CKM and PMNS imply that hidden symmetries may exist and be common for both quark and neutrino sectors. The CP phase of the CKM matrix (${\delta }_{\mathrm{CKM}}$) is involved in these equalities and can be investigated when these equalities turn into several equations. As we substitute those experimentally measured values of the three mixing angles into the equations for quarks, it is noted that one of the equations which holds exactly has a solution ${\delta }_{\mathrm{CKM}}=68.95^{\circ }$. That value accords with $(69.1_{-3.85}^{+2.02}{)}^{\circ }$ determined from available data. Generalizing the scenario to the lepton sector, the same equality determines the leptonic CP phase ${\delta }_{\mathrm{PMNS}}$ to be $276.10^{\circ }$. Thus we predict the value of ${\delta }_{\mathrm{PMNS}}$ from the equation. So far there is no direct measurement on ${\delta }_{\mathrm{PMNS}}$ yet, but a recent analysis based on the neutrino oscillation data prefers the phase close to $270^{\circ }$.

   hep-phhep-exJ.Phys.G(2017)·0 citations
7. 07*

   The decay of ${\Lambda }_b\to p{K}^{-}$ in QCD factorization approach

   Jie Zhu🇨🇳 · Hong-Wei Ke🇨🇳 · Zheng-Tao Wei🇨🇳

   With only the tree level operator, the decay of ${\Lambda }_b\to pK$ is predicted to be one order smaller than the experimental data. The QCD penguin effects should be taken into account. In this paper, we explore the one-loop QCD corrections to the decay of ${\Lambda }_b\to pK$ within the framework of QCD factorization approach. For the baryon system, the diquark approximation is adopted. The transition hadronic matrix elements between ${\Lambda }_b$ and $p$ are calculated in the light front quark model. The branching ratio of ${\Lambda }_b\to pK$ is predicted to be about $4.85\times 10^{-6}$ which is consistent with experimental data $(4.9\pm 0.9)\times 10^{-6}$. The CP violation is about 5\% in theory.

   hep-phEPJC(2016)·21 citations
8. 08*

   Primordial Magnetic Field Via Weibel Instability In The Quark Gluon Plasma Phase

   Abhishek Atreya🇮🇳 · Soma Sanyal🇮🇳

   The origin of the observed large scale magnetic fields in the Universe is a mystery. The seed of these magnetic fields has been attributed to physical process in the early universe. In this work we provide a mechanism for the generation of a primordial magnetic field in the early universe via the Weibel instability in the quark gluon plasma. The Weibel instability occurs in the plasma if there is an anisotropy in the particle distribution function of the particles. In early universe, the velocity anisotropy required for Weibel instability to operate is generated in the quark gluon plasma by the collapse of closed $Z(3)$ domain walls that arise in the deconfined phase of the QCD (above $T\sim 200$ MeV). Such large domains can arise in the context of certain low energy scale inflationary models. The closed domains undergo supersonic collapse and the velocity anisotropy is generated in the shocks produced in the wake of the collapsing domain walls. This results in a two stream Weibel instability in the ultra-relativistic quark gluon plasma. The instability in turn generates strong magnetic fields in the plasma. We find that the field strengths generated can be comparable to the equipartition energy density at the QCD scale which is of the order of $10^{18}$ G.

   hep-ph1 citation
9. 09*

   Dyson-Schwinger Approach to Color-Superconductivity: Effects of Selfconsistent Gluon Dressing

   Daniel Müller🇺🇸 · Michael Buballa🇩🇪 · Jochen Wambach🇮🇹

   The phase diagram of dense QCD at nonvanishing temperatures and large quark chemical potentials is studied with Dyson-Schwinger equations for 2+1 quark flavors, focusing on color-superconducting phases with 2SC and CFL-like pairing. The truncation scheme of our previous investigations is extended to include the dressing of gluons with selfconsistently determined quarks, i.e., taking into account the dynamical masses and superconducting gaps of the quarks in the gluon polarization. As a consequence the gluon screening is reduced, leading to an enhancement of the critical temperatures of the color-superconducting phases by about a factor of 2 as compared to the case where the gluons are dressed with bare quarks. We also calculate the Debye and Meissner masses of the gluons and show that they are consistent with weak-coupling results.

   hep-phnucl-th24 citations
10. 10*

    Flavor $SU(3)$ properties of beauty tetraquark states with three different light quarks

    Xiao-Gang He🇨🇳 · Pyungwon Ko🇰🇷

    Beauty tetraquark states $X(\bar{b}{q}^{\prime }{q}^{\prime \prime }\bar{q})$ composed of $\bar{b}su\bar{d}$, $\bar{b}ds\bar{u}$, and $\bar{b}ud\bar{s}$, are unique that all the four valence quarks are different. Although the claim of existence of the first two states by D0 was not confirmed by data from LHCb, the possibility of such states still generated a lot of interests and should be pursued further. Non-observation of $X(\bar{b}{q}^{\prime }{q}^{\prime \prime }\bar{q})$ states by LHCb may be just due to a still lower production rate than the limit of LHCb or at some different mass ranges. In this work we use light quark $SU(3)$ flavor symmetry as guideline to classify symmetry properties of beauty tetraquark states. The multiplets which contain states with three different light quarks must be one of $\bar{6}$ or $15$ of $SU(3)$ representations. We study possible decays of such a tetraquark state into a $B$ meson and a light pesudoscalar octet meson by constructing a leading order chiral Lagrangian, and also provide search strategies to determine whether a given tetraquark state of this type belongs to $\bar{6}$ or $15$. If $X(\bar{b}{q}^{\prime }{q}^{\prime \prime }\bar{q})$ belongs to $15$, there are new doubly charged tetraquark states $\bar{b}uu\bar{d}$ and $\bar{b}uu\bar{s}$.

    hep-phhep-exPLB(2016)·35 citations
11. 11*

    Holographic quark matter and neutron stars

    Carlos Hoyos🇪🇸 · David Rodríguez Fernández🇪🇸 · Niko Jokela🇫🇮 · Aleksi Vuorinen🇫🇮

    We use a top-down holographic model for strongly interacting quark matter to study the properties of neutron stars. When the corresponding Equation of State (EoS) is matched with state-of-the-art results for dense nuclear matter, we consistently observe a first order phase transition at densities between two and seven times the nuclear saturation density. Solving the Tolman-Oppenheimer-Volkov equations with the resulting hybrid EoSs, we find maximal stellar masses in the excess of two solar masses, albeit somewhat smaller than those obtained with simple extrapolations of the nuclear matter EoSs. Our calculation predicts that no quark matter exists inside neutron stars.

    hep-phastro-ph.HEhep-thPRL(2016)·101 citations
12. 12*

    Using ${\Lambda }_b\to \Lambda {\mu }^{+}{\mu }^{-}$ data within a Bayesian analysis of $|\Delta B|=|\Delta S|=1$ decays

    Stefan Meinel🇺🇸 · Danny van Dyk🇨🇭

    We study the impact of including the baryonic decay ${\Lambda }_b\to \Lambda (\to p{\pi }^{-}){\mu }^{+}{\mu }^{-}$ in a Bayesian analysis of $|\Delta B|=|\Delta S|=1$ transitions. We perform fits of the Wilson coefficients $C_9$, $C_{9^{\prime }}$, $C_{10}$ and $C_{10^{\prime }}$, in addition to the relevant nuisance parameters. Our analysis combines data for the differential branching fraction and three angular observables of ${\Lambda }_b\to \Lambda (\to p{\pi }^{-}){\mu }^{+}{\mu }^{-}$ with data for the branching ratios of $B_s\to {\mu }^{+}{\mu }^{-}$ and inclusive $b\to s{\ell }^{+}{\ell }^{-}$ decays. Newly available precise lattice QCD results for the full set of ${\Lambda }_b\to \Lambda$ form factors are used to evaluate the observables of the baryonic decay. Our fits prefer shifts to $C_9$ that are opposite in sign compared to those found in global fits of only mesonic decays, and the posterior odds show no evidence of physics beyond the Standard Model. We investigate a possible hadronic origin of the observed tensions between theory and experiment.

    hep-phPRD(2016)·48 citations
13. 13*

    QCD thermodynamics and magnetization in nonzero magnetic field

    Abdel Nasser Tawfik · Abdel Magied Diab · Nada Ezzelarab (Egyptian Ctr. Theor. Phys., Cairo and WLCAPP, Cairo) Asmaa G. Shalaby (Benha U., WLCAPP, Cairo)

    In nonzero magnetic field, the magnetic properties and thermodynamics of the quantum-chromodynamic (QCD) matter is studied in the hadron resonance gas and the Polyakov linear-sigma models and compared with recent lattice calculations. Both models are fairly suited to describe the degrees of freedom in the hadronic phase. The partonic ones are only accessible by the second model. It is found that the QCD matter has paramagnetic properties, which monotonically depend on the temperature and are not affected by the hadron-quark phase-transition. Furthermore, raising the magnetic field strength increases the thermodynamic quantities, especially in the hadronic phase but reduces the critical temperature, i.e. inverse magnetic catalysis.

    hep-phhep-lathep-thAdv.High Energy Phys.(2016)·36 citations
14. 14*

    Preheating in an Asymptotically Safe Quantum Field Theory

    Ole Svendsen🇩🇰 · Hossein Bazrafshan Moghaddam🇨🇦 · Robert Brandenberger🇨🇦

    We consider reheating in a class of asymptotically safe quantum field theories recently studied in \cite{Litim:2014uca, Litim:2015iea}. These theories allow for an inflationary phase in the very early universe. Inflation ends with a period of reheating. Since the models contain many scalar fields which are intrinsically coupled to the inflaton there is the possibility of parametric resonance instability in the production of these fields, and the danger that the induced curvature fluctuations will become too large. Here we show that the parametric instability indeed arises, and that hence the energy transfer from the inflaton condensate to fluctuating fields is rapid. Demanding that the curvature fluctuations induced by the parametrically amplified entropy modes do not exceed the upper observational bounds puts a lower bound on the number of fields which the model of Ref.~\cite{Litim:2014uca, Litim:2015iea} must contain. This bound also depends on the total number of e-foldings of the inflationary phase.

    ↳ hep-thastro-ph.COgr-qchep-phPRD(2016)·11 citations
15. 15*

    Insight from elliptic flow of open charm mesons using quark coalescence model at RHIC and LHC energies

    Roli Esha🇺🇸 · Md. Nasim🇺🇸 · Huan Zhong Huang🇺🇸

    A study of elliptic flow of open charm mesons, $D^0$ and $D_S^{\pm }$ using quark coalescence as a mechanism of hadronization of heavy quarks implemented in conjunction with A Multi Phase Transport (AMPT) model has been presented. We have studied the transverse momentum dependence of the elliptic flow parameter at mid-rapidity ($|y|$ $<$ 1.0) for Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV (RHIC) and Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV (LHC) for different values of partonic interaction cross-section and QCD coupling constant. We have compared our calculations with the experimentally measured data at the LHC energy. We have also studied the effect of shear viscosity on elliptic flow of open charm mesons within the transport model approach. Our study indicates that the elliptic flow of open charmed mesons is more sensitive to viscous properties of QGP medium as compared to light charged hadrons.

    ↳ nucl-thhep-phnucl-exJ.Phys.G(2017)·15 citations
16. 16*

    Baryons and the Borromeo

    Craig D. Roberts🇺🇸 · Jorge Segovia🇩🇪

    The kernels in the tangible matter of our everyday experience are composed of light quarks. At least, they are light classically; but they don't remain light. Dynamical effects within the Standard Model of Particle Physics change them in remarkable ways, so that in some configurations they appear nearly massless, but in others possess masses on the scale of light nuclei. Modern experiment and theory are exposing the mechanisms responsible for these remarkable transformations. The rewards are great if we can combine the emerging sketches into an accurate picture of confinement, which is such a singular feature of the Standard Model; and looming larger amongst the emerging ideas is a perspective that leads to a Borromean picture of the proton and its excited states.

    ↳ nucl-thhep-lathep-phnucl-exFew Body Syst.(2016)·21 citations
17. 17*

    Cosmological hysteresis in cyclic universe from membrane paradigm

    Sayantan Choudhury🇮🇳 · Shreya Banerjee🇮🇳

    Cosmological hysteresis is a purely thermodynamical phenomenon caused by the gradient in pressure, hence the characteristic equation of state during the expansion and contraction phases of the universe are different, provided that the universe bounces and recollapses. During hysteresis pressure asymmetry is created due to the presence of a single scalar field in the dynamical process. Also such an interesting scenario has vivid implications in cosmology when applied to variants of modified gravity models described within the framework of membrane paradigm. Cyclic universe along with scalar field leads to the increase in the amplitude of the cosmological scale factor at each consecutive cycles of the universe. Detailed analysis shows that the conditions which creates a universe with an ever increasing expansion, depend on the signature of the hysteresis loop integral $\oint pdV$ and on membrane model parameters.

    ↳ hep-thastro-ph.COgr-qchep-ph4 citations
18. 18*

    Hadron production within PHSD

    Pierre Moreau🇩🇪 · Wolfgang Cassing🇩🇪 · Alessia Palmese🇩🇪 · Elena Bratkovskaya🇩🇪

    We study the production of hadrons in nucleus-nucleus collisions within the Parton-Hadron-String Dynamics (PHSD) transport approach that is extended to incorporate essentials aspects of chiral symmetry restoration (CSR) in the hadronic sector (via the Schwinger mechanism) on top of the deconfinement phase transition as implemented in PHSD. The essential impact of CSR is found in the Schwinger mechanism (for string decay) which fixes the ratio of strange to light quark production in the hadronic medium. Our studies provide a microscopic explanation for the maximum in the $K^{+}/{\pi }^{+}$ ratio at about 30 A GeV which only shows up if in addition to CSR a deconfinement transition to partonic degrees-of-freedom is incorporated in the reaction dynamics.

    ↳ nucl-thhep-phActa Phys.Polon.Supp.(2016)·0 citations
19. 19*

    Quantum canonical ensemble and correlation femtoscopy at fixed multiplicities

    S.V. Akkelin🇺🇦 · Yu.M. Sinyukov🇺🇦

    Identical particle correlations at fixed multiplicity are considered by means of quantum canonical ensemble of finite systems. We calculate one-particle momentum spectra and two-particle Bose-Einstein correlation functions in the ideal gas by using a recurrence relation for the partition function. Within such a model we investigate the validity of the thermal Wick's theorem and its applicability for decomposition of the two-particle distribution function. The dependence of the Bose-Einstein correlation parameters on the average momentum of the particle pair is also investigated. Specifically, we present the analytical formulas that allow one to estimate the effect of suppressing the correlation functions in a finite canonical system. The results can be used for the femtoscopy analysis of the A+A and p+p collisions with selected (fixed) multiplicity.

    ↳ nucl-thhep-exhep-phnucl-exPRC(2016)·3 citations
20. 20*

    Massive and modified gravity as self-gravitating media

    Guillermo Ballesteros🇫🇷 · Denis Comelli🇮🇹 · Luigi Pilo🇮🇹

    We study the effective field theory that describes the low-energy physics of self-gravitating media. The field content consists of four derivatively coupled scalar fields that can be identified with the internal comoving coordinates of the medium. Imposing SO(3) internal spatial invariance, the theory describes supersolids. Stronger symmetry requirements lead to superfluids, solids and perfect fluids, at lowest order in derivatives. In the unitary gauge, massive gravity emerges, being thus the result of a continuous medium propagating in spacetime. Our results can be used to explore systematically the effects and signatures of modifying gravity consistently at large distances. The dark sector is then described as a self-gravitating medium with dynamical and thermodynamic properties dictated by internal symmetries. These results indicate that the divide between dark energy and modified gravity, at large distance scales, is simply a gauge choice.

    ↳ hep-thastro-ph.COgr-qchep-phPRD(2016)·38 citations
21. 21*

    Erratum: Standard-model prediction for direct CP violation in $K\to \pi \pi$ decay

    Z. Bai🇺🇸 · T. Blum🇺🇸 · P. A. Boyle🇬🇧 · N. H. Christ🇺🇸 · J. Frison🇬🇧 · N.Garron🇬🇧 · T. Izubuchi🇺🇸 · C. Jung🇺🇸 · C. Kelly🇺🇸 · C. Lehner🇺🇸 · R. D. Mawhinney🇺🇸 · C. T. Sachrajda🇬🇧 · A. Soni🇺🇸 · D. Zhang🇺🇸

    In this document we address an error discovered in the ensemble generation for our calculation of the $I=0$ $K\to \pi \pi$ amplitude (Phys. Rev. Lett. 115, 212001 (2015), arXiv:1505.07863) whereby the same random numbers were used for the two independent quark flavors, resulting in small but measurable correlations between gauge observables separated by 12 units in the y-direction. We conclude that the effects of this error are negligible compared to the overall errors on our calculation.

    ↳ hep-lathep-ph10 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.