Nuclear Theory·nucl-th

Monday·July 20, 2015

10 papers—4 primary·6 cross-listed

01
[Submitted on 17 Jul 2015]
Fluctuations in slope parameter in event-by-event hydrodynamics and momentum anisotropy in heavy ion collisions
A. K. Chaudhuri🇮🇳
In event by event hydrodynamic model, we have simulated 30-40\% Au+Au collisions at RHIC and computed the slope parameter from the invariant pion distribution. In each event, the slope parameter fluctuates azimuthally. Fourier expansion coefficients $T_{n}$ for the slope parameter and the Fourier expansion coefficients $v_{n}$ for the azimuthal distribution $\frac{d N}{d ϕ}$ are found to be strongly correlated. Strong correlation between the two expansion coefficients suggests that in addition to azimuthal distribution, fluctuations in the slope parameter of the invariant distribution can as well be used to study the final state momentum anisotropy in relativistic energy heavy ion collisions. If measured experimentally, they can serve as additional constraint for hydrodynamical modeling.
Comments:
6 pages, 4 figures. arXiv admin note: text overlap with arXiv:1210.2249
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1507.04898 [pdf]
1 citation
02
[Submitted on 17 Jul 2015]
Probing the properties of event-by-event distributions in Hanbury-Brown--Twiss radii
Christopher Plumberg · Ulrich Heinz
Hanbury-Brown--Twiss interferometry is a technique which yields effective widths (i.e., "HBT radii") of homogeneity regions in the fireballs produced in heavy ion collisions. Because the initial conditions of these collisions are stochastically fluctuating, the measured HBT radii also exhibit variation on an event-by-event basis. However, HBT measurements have, to date, been performed only on an ensemble-averaged basis, due to inherent limitations of finite particle statistics. In this paper, we show that experimental measurements to date are best characterized theoretically as weighted averages of the event-by-event HBT radii, and we propose a new method for extracting experimentally both the arithmetic mean and the variance of the event-by-event distribution of HBT radii. We demonstrate the extraction of the mean and variance of this distribution for a particular ensemble of numerically generated events, and offer some ideas to extend and generalize the method to enable measurement of higher moments of the HBT distribution as well.
Comments:
V1 - 18 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1507.04968 [pdf]
PRC(2015)·13 citations
03
[Submitted on 17 Jul 2015]
Time evolution of the anisotropies of the hydrodynamically expanding sQGP
Attila Bagoly🇭🇺 · Mate Csanad🇭🇺
In high energy heavy ion collisions of RHIC and LHC, a strongly interacting quark gluon plasma (sQGP) is created. This medium undergoes a hydrodynamic evolution, before it freezes out to form a hadronic matter. The initial state of the sQGP is determined by the initial distribution of the participating nucleons and their interactions. Due to the finite number of nucleons, the initial distribution fluctuates on an event-by-event basis. The transverse plane anisotropy of the initial state can be translated into a series of anisotropy coefficients or eccentricities: second, third, fourth-order anisotropy etc. These anisotropies then evolve in time, and result in measurable momentum-space anisotropies, to be measured with respect to their respective symmetry planes. In this paper we investigate the time evolution of the anisotropies. With a numerical hydrodynamic code, we analyze how the speed of sound and viscosity influence this evolution.
Comments:
10 pages, 6 figures. To appear in the Gribov-85 Memorial Workshop's proceedings volume. Supported by OTKA NK 101438
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1507.05005 [pdf]
Int.J.Mod.Phys.A(2016)·2 citations
04
[Submitted on 17 Jul 2015]
Analytical mass formula and nuclear surface properties in the ETF approximation
F. Aymard🇫🇷 · F. Gulminelli🇫🇷 · J. Margueron🇫🇷
The problem of the determination of the nuclear surface and surface symmetry energy is addressed in the framework of the Extended Thomas Fermi (ETF) approximation using Skyrme functionals. We propose an analytical model for the density profiles with variationally determined diffuseness parameters. For the case of symmetric nuclei, the resulting ETF functional can be exactly integrated, leading to an analytical formula expressing the surface energy as a function of the couplings of the energy functional. The importance of non-local terms is stressed, which cannot be simply deduced from the local part of the functional. In the case of asymmetric nuclei, we propose an approximate expression for the diffuseness and the surface energy. These quantities are analytically related to the parameters of the energy functional. In particular, the influence of the different equation of state parameters can be explicitly quantified. Detailed analyses of the different energy components (local/non-local, isoscalar/isovector, surface/curvature and higher order) are also performed. Our analytical solution of the ETF integral improves over previous models and leads to a precision better than 200 keV per nucleon in the determination of the nuclear binding energy for dripline nuclei.
Comments:
27 pages, 18 figures, submitted to PRC
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1507.05064 [pdf]
J.Phys.G(2016)·7 citations
05
[Submitted on 1 Jul 2015] (cross-list from cond-mat.quant-gas)
Simulation of Time-dependent Heisenberg Models in 1D
A. G. Volosniev · H.-W. Hammer · N. T. Zinner
In this paper, we provide a theoretical analysis of strongly interacting quantum systems confined by a time-dependent external potential in one spatial dimension. We show that such systems can be used to simulate spin chains described by Heisenberg Hamiltonians in which the exchange coupling constants can be manipulated by time-dependent driving of the shape of the external confinement. As illustrative examples, we consider a harmonic trapping potential with a variable frequency and an infinite square well potential with a time-dependent barrier in the middle.
Comments:
Version accepted for publication in PRB
Subjects:
Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th)
arXiv:
1507.00186 [pdf]
PRB(2016)·16 citations
06
[Submitted on 16 Jul 2015] (cross-list from astro-ph.SR)
Some properties of convection in hybrid stars
A.V. Yudin · M. Hempel · D.K. Nadyozhin · T.L. Razinkova
It is shown that the unusual thermodynamic properties of matter within the region of two-phase coexistence in hybrid stars result in a change of the standard condition for beginning of convection. In particular, the thermal flux transported by convection may be directed towards the stellar center. We discuss favorable circumstances leading to such an effect of "inverse convection" and its possible influence on the thermal evolution of hybrid stars.
Comments:
13 pages, 3 figures. The discussion is extended according to referees suggestions. New references added. Accepted to MNRAS
Subjects:
Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1507.04598 [pdf]
MNRAS(2016)·7 citations
07
[Submitted on 16 Jul 2015] (cross-list from hep-ph)
Critical versus spurious fluctuations in the search for the QCD critical point
Maurício Hippert🇧🇷 · Eduardo S. Fraga🇧🇷 · Edivaldo M. Santos🇧🇷
The neighborhood of the QCD chiral critical point is characterized by intense fluctuations of the chiral field which could, in principle, generate pronounced experimental signatures. However, experimental uncertainties which are inherent to heavy ion collisions, as well as the modest size and duration of the formed plasma, will severely attenuate these signatures. Using Monte Carlo techniques, we study second-order event-by-event moments of pions as a prototype for signatures of the chiral critical point based on the enhancement of the correlation length and event-by-event analysis. We test their viability against some realistic ingredients, similar to the ones found in the RHIC Beam Energy Scan program.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1507.04764 [pdf]
PRD(2016)·18 citations
08
[Submitted on 17 Jul 2015] (cross-list from hep-ph)
Derivation of second-order relativistic hydrodynamics for reactive multi-component systems
Yuta Kikuchi🇯🇵 · Kyosuke Tsumura🇯🇵 · Teiji Kunihiro🇯🇵
We derive the second-order hydrodynamic equation for reactive multi-component systems from the relativistic Boltzmann equation. In the reactive system, particles can change their species under the restriction of the imposed conservation laws during the collision process. Our derivation is based on the renormalization group (RG) method, in which the Boltzmann equation is solved in an organized perturbation method as faithfully as possible and possible secular terms are resummed away by a suitable setting of the initial value of the distribution function. The microscopic formulae of the relaxation times and the lengths are explicitly given as well as those of the transport coefficients for the reactive multi-component system. The resultant hydrodynamic equation with these formulae has nice properties that it satisfies the positivity of the entropy production rate and the Onsager's reciprocal theorem, which ensure the validity of our derivation.
Comments:
18 pages, 2 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th); Fluid Dynamics (physics.flu-dyn)
arXiv:
1507.04894 [pdf]
PRC(2015)·21 citations
09
[Submitted on 17 Jul 2015] (cross-list from hep-lat)
Nucleon and pion structure with lattice QCD simulations at physical value of the pion mass
A. Abdel-Rehim (Cyprus Inst.)🇨🇾 · C. Alexandrou (Cyprus Inst. & Univ. of Cyprus)🇨🇾 · M. Constantinou (Cyprus Inst. & Univ. of Cyprus)🇨🇾 · P. Dimopoulos (Fermi Center & Rome Tor Vergata)🇮🇹 · R. Frezzotti (INFN & Rome Tor Vergata)🇮🇹 · K. Hadjiyiannakou (Univ. of Cyprus & Cyprus Inst.)🇨🇾 · K. Jansen (DESY)🇩🇪 · Ch. Kallidonis (Cyprus Inst.)🇨🇾 · B. Kostrzewa (Humboldt Univ. & DESY)🇩🇪 · G. Koutsou (Cyprus Inst.)🇨🇾 · M. Mangin-Brinet (Grenoble)🇫🇷 · M. Oehm (Bonn Univ.)🇩🇪 and 3 other authors
We present results on the nucleon scalar, axial and tensor charges as well as on the momentum fraction, and the helicity and transversity moments. The pion momentum fraction is also presented. The computation of these key observables is carried out using lattice QCD simulations at a physical value of the pion mass. The evaluation is based on gauge configurations generated with two degenerate sea quarks of twisted mass fermions with a clover term. We investigate excited states contributions with the nucleon quantum numbers by analyzing three sink-source time separations. We find that, for the scalar charge, excited states contribute significantly and to a less degree to the nucleon momentum fraction and helicity moment. Our analysis yields a value for the nucleon axial charge agrees with the experimental value and we predict a value of 1.027(62) in the $MS$ scheme at 2 GeV for the isovector nucleon tensor charge directly at the physical point. The pion momentum fraction is found to be $⟨ x ⟩_{u - d}^{π^{\pm}} = 0.214 (15) (_{- 9}^{+ 12})$ in the $MS$ at 2 GeV.
Comments:
The experimental value of the helicity plotted in Fig.17 is corrected. ETM Collaboration. 25 pages, 19 figures. Version accepted for PRD (volume 92, eid 114513)
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1507.04936 [pdf]
PRD(2015)·175 citations
10
[Submitted on 17 Jul 2015] (cross-list from hep-ph)
Tetraquarks from the Bethe-Salpeter equation
Gernot Eichmann🇩🇪 · Christian S. Fischer🇩🇪 · Walter Heupel🇩🇪
We present a numerical solution of the four-quark Bethe-Salpeter equation for a scalar tetraquark. We find that the four-body equation dynamically generates pseudoscalar poles in the Bethe-Salpeter amplitude. The sensitivity to the pion poles leads to a light isoscalar tetraquark mass M ~ 400 MeV, which is comparable to that of the sigma/f0(500). The masses of its multiplet partners kappa and a0/f0 follow a similar pattern, thereby providing support for the tetraquark interpretation of the light scalar nonet.
Comments:
7 pages, 4 figures. Proceedings of the workshop "Excited QCD 2015", Tatranska Lomnica, Slovakia, March 8-14, 2015. To be published in Acta Physica Polonica B Proc. Suppl
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1507.05022 [pdf]
Acta Phys.Polon.Supp.(2015)·7 citations

Affiliations

first authorsco-authorsvia INSPIRE