Nuclear Theory·nucl-th

Thursday·March 31, 2016

12 papers—5 primary·7 cross-listed

06
Role of nonlocal probes of thermalization for a strongly interacting non-Abelian plasma
Loredana Bellantuono🇮🇹 · Pietro Colangelo🇮🇹 · Fulvia De Fazio🇮🇹 · Floriana Giannuzzi🇮🇹 · Stefano Nicotri🇮🇹
We use a holographic method to investigate thermalization of a boost-invariant strongly interacting non-Abelian plasma. Boundary sourcing, a distorsion of the boundary metric, is employed to drive the system far from equilibrium. Thermalization is analyzed through nonlocal probes: the equal-time two-point correlation function of large conformal dimension operators in the boundary theory, and Wilson loops of different shapes. We study the dependence of the thermalization time on the size of the probes, and compare the results to the ones obtained using local observables: the onset of thermalization is first observed at short distances.
↳ hep-phhep-thnucl-thPRD(2016)·18 citations
07
Color Instabilities in the Quark-Gluon Plasma
Stanislaw Mrowczynski🇵🇱 · Bjoern Schenke🇺🇸 · Michael Strickland🇩🇪
When the quark-gluon plasma (QGP) - a system of deconfined quarks and gluons - is in a nonequilibrium state, it is usually unstable with respect to color collective modes. The instabilities, which are expected to strongly influence dynamics of the QGP produced in relativistic heavy-ion collisions, are extensively discussed under the assumption that the plasma is weakly coupled. We begin by presenting the theoretical approaches to study the QGP, which include: field theory methods based on the Keldysh-Schwinger formalism, classical and kinetic theories, and fluid techniques. The dispersion equations, which give the spectrum of plasma collective excitations, are analyzed in detail. Particular attention is paid to a momentum distribution of plasma constituents which is obtained by deforming an isotropic momentum distribution. Mechanisms of chromoelectric and chromomagnetic instabilities are explained in terms of elementary physics. The Nyquist analysis, which allows one to determine the number of solutions of a dispersion equation without explicitly solving it, and stability criteria are also discussed. We then review various numerical approaches - purely classical or quantum - to simulate the temporal evolution of an unstable quark-gluon plasma. The dynamical role of instabilities in the processes of plasma equilibration is analyzed.
↳ hep-phhep-thnucl-thPhys.Rept.(2017)·90 citations
08
Evaluation of reactor neutrino flux: issues and uncertainties
Petr Vogel🇺🇸
Evaluation of the reactor $ν ˉ_{e}$ flux and spectrum is an essential ingredient of their application in the neutrino oscillation studies. Two anomalies, i.e. discrepancies between the observed and expected count rates, are widely discussed at the resent time. The total rate is $\sim$ 6\% lower than the expectation at all distances $>$ 10 m from the reactor. And there is a shoulder (often referred to as "bump") at neutrino energies 5-7 MeV, not predicted in the calculated spectrum. I review the ways the flux and spectrum is evaluated and concentrate on the error budget. I argue that far reaching conclusions based on these anomalies should await a thorough understanding of the uncertainties of the spectrum, and point out possible standard physics sources of the anomalies.
↳ hep-phnucl-th8 citations
09
Centrality dependence of midrapidity density from GeV to TeV heavy-ion collisions in the effective-energy universality picture of hadroproduction
Edward K.G. Sarkisyan🇨🇭 · Aditya Nath Mishra🇮🇳 · Raghunath Sahoo🇮🇳 · Alexander S. Sakharov🇨🇭
The dependence on centrality, or on the number of nucleon participants, of the midrapidity density of charged particles measured in heavy-ion collisions at the collision energy of about 20 GeV at RHIC to the highest LHC energy of 5 TeV is investigated within the recently proposed effective-energy approach. This approach relates multihadron production in different types of collisions by combining, under the proper scaling of the collision energy, the constituent quark picture with Landau relativistic hydrodynamics. The measurements are shown to be well described based on the similarity of multihadron production process in (anti)proton-proton interactions and heavy-ion collisions driven by the centrality-dependent effective energy of participants.
↳ hep-phhep-exnucl-exnucl-thPRD(2016)·50 citations
10
Can $X (5568)$ be described as a $B_{s} π$ , $B K ˉ$ resonant state?
Miguel Albaladejo🇪🇸 · Juan Nieves🇪🇸 · Eulogio Oset🇪🇸 · Zhi-Feng Sun🇪🇸 · Xiang Liu🇨🇳
The D0 Collaboration has recently seen a resonant-like peak in the $B_{s} π$ invariant mass spectrum, claimed to be a new state called $X (5568)$ . Using a $B_{s} π$ -- $B K ˉ$ coupled channel analysis, implementing unitarity, and with the interaction derived from Heavy Meson Chiral Perturbation Theory, we are able to reproduce the reported spectrum, with a pole that can be associated to the claimed $X (5568)$ state, and with mass and width in agreement with the ones reported in the experimental analysis. However, if the $T$ -matrix regularization is performed by means of a momentum cutoff, the value for the latter needed to reproduce the spectrum is $Λ = 2.80 \pm 0.04 GeV$ , much larger than a "natural" value $Λ ≃ 1 GeV$ . In view of this, it is difficult to interpret the nature of this new state. This state would not qualify as a resonance dynamically generated by the unitarity loops. Assuming the observed peak to correspond to a physical state, we make predictions for partners in the $D$ , $D^{*}$ , and $B^{*}$ sectors. Their observation (or lack thereof) would shed light into this issue.
↳ hep-phnucl-thPLB(2016)·56 citations
11
40 years of the Nobel prize in physics: then and now
Ricardo A.Broglia
The findings for which Aage Bohr and Ben R. Mottelson became co-winners of the 1975 Nobel prize in physics provided the basis for a comprehensive and operative answer to the central problem in the study of the nuclear structure, namely the identification of the appropriate concepts and degrees of freedom that are suitable for describing the phenomena encountered. To do so they produced a breathtaking unification of a number of well established concepts, namely liquid drop and shell models, elementary modes of excitation, superconductivity and quantum electrodynamics, resulting eventually in the paradigm of broken symmetry restoration to determine the nuclear collective variables (CV, elementary modes of excitation): violation of translation invariance by the mean field and by scattering states (single-particle motion), of rotational invariance in the variety of spaces, in particular in 3D- and in gauge-space, leading to surface vibrations and to quadrupole rotations, as well as to pairing vibrations and rotations, with associated emergent properties of generalized rigidity in these spaces, resulting from the coupling to single-particle degrees of freedom.
↳ physics.hist-phnucl-th0 citations
12
Relating $q^$ , $η / s$ and $Δ E$ in an expanding Quark-Gluon Plasma
Alejandro Ayala🇿🇦 · Isabel Dominguez🇲🇽 · Jamal Jalilian-Marian🇺🇸 · Maria Elena Tejeda-Yeomans🇲🇽
We use linear viscous hydrodynamics to describe the energy and momentum deposited by a fast moving parton in a quark gluon plasma. This energy-momentum is in turn used to compute the probability density for the production of soft partons by means of the Cooper-Frye formula. We use this probability density to render manifest a relation between the average transverse momentum given to the fast moving parton from the medium $q^$ , the entropy density to shear viscosity ratio $η / s$ and the energy lost by the fast moving parton $Δ E$ in an expanding medium under similar conditions to those generated in nucleus-nucleus collisions at the LHC. We find that $q^$ increases linearly with $Δ E$ for both trigger and away side partons that have been produced throughout the medium. On the other hand, $η / s$ is more stable with $Δ E$ . We also study how these transport coefficients vary with the geometrical location of the hard scattering that produces the fast moving partons. The behavior of $q^$ , with $Δ E$ is understood as arising from the length of medium the parton traverses from the point where it is produced. However, since $η / s$ is proportional to the ratio of the length of medium traversed by the fast parton and the average number of scatterings it experiences, it has a milder dependence on the energy it loses. This study represents a tool to obtain a direct connection between transport coefficients and the description of in-medium energy loss within a linear viscous hydrodynamical evolution of the bulk.
↳ hep-phnucl-thPRC(2016)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE

Role of nonlocal probes of thermalization for a strongly interacting non-Abelian plasma

Color Instabilities in the Quark-Gluon Plasma

Evaluation of reactor neutrino flux: issues and uncertainties

Centrality dependence of midrapidity density from GeV to TeV heavy-ion collisions in the effective-energy universality picture of hadroproduction

Can X(5568) be described as a Bs​π, BKˉ resonant state?

40 years of the Nobel prize in physics: then and now

Relating q^​, η/s and ΔE in an expanding Quark-Gluon Plasma

Affiliations

Can $X (5568)$ be described as a $B_{s} π$ , $B K ˉ$ resonant state?

Relating $q^$ , $η / s$ and $Δ E$ in an expanding Quark-Gluon Plasma