Nuclear Theory·nucl-th

Tuesday·August 25, 2015

18 papers—8 primary·10 cross-listed

09
[Submitted on 21 Aug 2015] (cross-list from hep-ph)
Anisotropic emission of thermal dielectrons from Au+Au collisions at $s_{N N} = 200$ ~GeV with EPOS3
Sheng-Xu Liu🇨🇳 · Fu-Ming Liu🇨🇳 · Klaus Werner🇫🇷 · Meng Yue🇨🇳
Dileptons, as an electromagnetic probe, are crucial to study the properties of a Quark-Gluon Plasma (QGP) created in heavy ion collisions. We calculated the invariant mass spectra and the anisotropic emission of thermal dielectrons from Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) energy $s_{N N} = 200$ ~GeV based on EPOS3. This approach provides a realistic (3+1)-dimensional event-by-event viscous hydrodynamic description of the expanding hot and dense matter with a very particular initial condition, and a large set of hadron data and direct photons (besides $v_{2}$ and $v_{3}$ !) can be successfully reproduced. Thermal dilepton emission from both the QGP phase and the hadronic gas are considered, with the emission rates based on Lattice QCD and a vector meson model, respectively. We find that the computed invariant mass spectra (thermal contribution + STAR cocktail) can reproduce the measured ones from STAR at different centralities. Different compared to other model predictions, the obtained elliptic flow of thermal dileptons is larger than the STAR measurement referring to all dileptons. We observe a clear centrality dependence of thermal dilepton not only for elliptic flow $v_{2}$ but also for higher orders. At a given centrality, $v_{n}$ of thermal dileptons decreases monotonically with $n$ for $2 \leq n \leq 5$ .
Comments:
10pages, 12figs
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1508.05160 [pdf]
0 citations
10
[Submitted on 21 Aug 2015] (cross-list from hep-ph)
Small-x, Diffraction and Vector Mesons
T. Lappi🇫🇮
This talk discusses recent progress in some topics relevant for deep inelastic scattering at small x. We discuss first differences and similarities between conventional collinear factorization and the dipole picture of deep inelastic scattering. Many of the recent theoretical advances at small x are related to taking calculations in the nonlinear saturation regime to next-to-leading order accuracy in the QCD coupling. On the experimental side significant recent progress has been made in exclusive and diffractive processes, in particular in ultraperipheral nucleus-nucleus collisions.
Comments:
15 pages, 14 figures. Plenary talk at DIS 2015, Dallas, TX, April 2015
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1508.05180 [pdf]
PoS(2015)·0 citations
11
[Submitted on 21 Aug 2015] (cross-list from hep-ph)
Scale-Invariant Hidden Local Symmetry, Topology Change and Dense Baryonic Matter
Won-Gi Paeng🇰🇷 · Thomas T. S. Kuo🇺🇸 · Hyun Kyu Lee🇰🇷 · Mannque Rho🇫🇷
When scale symmetry is implemented into hidden local symmetry in low-energy strong interactions to arrive at a scale-invariant hidden local symmetric (HLS) theory, the scalar $f_{0} (500)$ may be interpreted as pseudo-Nambu-Goldstone (pNG) boson, i.e., dilaton, of spontaneously broken scale invariance, joining the pseudo-scalar pNG bosons $π$ and the matter fields $V = (ρ, ω)$ as relevant degrees of freedom. Implementing the skyrmion-half-skyrmion transition predicted at large $N_{c}$ in QCD at a density roughly twice the nuclear matter density found in the crystal simulation of dense skyrmion matter, we determine the intrinsically density-dependent (IDD) "bare parameters" of the scale-invariant HLS Lagrangian matched to QCD at a matching scale $Λ_{M}$ . The resulting effective Lagrangian, with the parameters scaling with the density of the system, is applied to nuclear matter and dense baryonic matter relevant to massive compact stars by means of the double-decimation renormalization-group $V_{l o w k}$ formalism. We satisfactorily post-dict the properties of normal nuclear matter and more significantly {\it predict} the EoS of dense compact-star matter that quantitatively accounts for the presently available data coming from both the terrestrial and space laboratories. We interpret the resulting structure of compact-star matter as revealing how the combination of hidden-scale symmetry and hidden local symmetry manifests itself in compressed baryonic matter.
Comments:
37 pages and 14 figures, Revised for publication
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1508.05210 [pdf]
PRC(2016)·48 citations
12
[Submitted on 21 Aug 2015] (cross-list from hep-ph)
Debye mass at the QCD transition in the PNJL model
J. Jankowski🇵🇱 · D. Blaschke🇷🇺 · O. Kaczmarek🇩🇪
We consider colour-electric screening as expressed by the quark contribution to the Debye mass calculated in a PNJL model with emphasis on confining and chiral symmetry breaking effects. We observe that the screening mass is entirely determined by the nonperturbative quark distribution function and temperature dependent QCD running coupling. The role of the gluon background (Polyakov loop) is to provide strong suppression of the number of charge carriers below the transition temperature, as an effect of confinement, while the temperature dependent dynamical quark mass contributes additional suppression, as an effect of chiral symmetry breaking. An alternative derivation of this result from a modified kinetic theory is given, which allows for a slight generalization and explicit contact with perturbative QCD. This gives the possibility to gain insights into the colour screening mechanism in the region near the QCD pseudocritical temperature and to provide a guideline for the interpretation of lattice QCD data.
Comments:
9 pages, 2 figures, references, text and acknowledgement added, typos corrected
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1508.05322 [pdf]
3 citations
13
[Submitted on 21 Aug 2015] (cross-list from hep-ph)
Two-Step Electroweak Baryogenesis
Satoru Inoue🇺🇸 · Grigory Ovanesyan🇺🇸 · Michael J. Ramsey-Musolf🇺🇸
We analyze electroweak baryogenesis during a two-step electroweak symmetry breaking transition, wherein the baryon asymmetry is generated during the first step and preserved during the second. Focusing on the dynamics of CP-violation required for asymmetry generation, we discuss general considerations for successful two-step baryogenesis. Using a concrete model realization, we illustrate in detail the viability of this scenario and the implications for present and future electric dipole moment (EDM) searches. We find that CP-violation associated with a partially excluded sector may yield the observed baryon asymmetry while evading present and future EDM constraints.
Comments:
20 pages, 11 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1508.05404 [pdf]
PRD(2016)·102 citations
14
[Submitted on 22 Aug 2015] (cross-list from astro-ph.HE)
Exploring properties of high-density matter through remnants of neutron-star mergers
Andreas Bauswein🇬🇷 · Nikolaos Stergioulas🇬🇷 · Hans-Thomas Janka🇩🇪
Remnants of neutron-star mergers are essentially massive, hot, differentially rotating neutron stars, which are initially strongly oscillating. They represent a unique probe for high-density matter because the oscillations are detectable via gravitational-wave measurements and are strongly dependent on the equation of state. The impact of the equation of state is apparent in the frequency of the dominant oscillation mode of the remnant. For a fixed total binary mass a tight relation between the dominant postmerger frequency and the radii of nonrotating neutron stars exists. Inferring observationally the dominant postmerger frequency thus determines neutron star radii with high accuracy of the order of a few hundred meters. By considering symmetric and asymmetric binaries of the same chirp mass, we show that the knowledge of the binary mass ratio is not critical for this kind of radius measurements. We summarize different possibilities to deduce the maximum mass of nonrotating neutron stars. We clarify the nature of the three most prominent features of the postmerger gravitational-wave spectrum and argue that the merger remnant can be considered to be a single, isolated, self-gravitating object that can be described by concepts of asteroseismology. The understanding of the different mechanisms shaping the gravitational-wave signal yields a physically motivated analytic model of the gravitational-wave emission, which may form the basis for template-based gravitational-wave data analysis. We explore the observational consequences of a scenario of two families of compact stars including hadronic and quark stars. We find that this scenario leaves a distinctive imprint on the postmerger gravitational-wave signal. In particular, a strong discontinuity in the dominant postmerger frequency as function of the total mass will be a strong indication for two families of compact stars. (abridged)
Comments:
22 pages, 17 figures; accepted for publication in EPJA
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1508.05493 [pdf]
EPJA(2016)·162 citations
15
[Submitted on 22 Aug 2015] (cross-list from astro-ph.HE)
From quark drops to quark stars: some aspects of the role of quark matter in compact stars
Germán Lugones🇧🇷
We review some recent results about the mechanism of deconfinement of hadronic matter into quark matter in cold neutron stars and protoneutron stars. We discuss the role of finite size effects and the relevance of temperature and density fluctuations on the nucleation process. We also examine the importance of surface effects for mixed phases in hybrid stars. A small drop of quark matter nucleated at the core of a compact star may grow if the conversion is sufficiently exothermic. In such a case, it may trigger the burning of the stellar core and even the whole star if quark matter is absolutely stable. We explore the physical processes that occur inside the flame and analyze the hydrodynamic evolution of the combustion front. In the last part of this review, we focus on hybrid stars using the Nambu-Jona-Lasinio (NJL) model with scalar, vector and 't Hooft interactions, paying particular attention to a generalized non-standard procedure for the choice of the 'bag constant'. We also describe the non-radial oscillation modes of hadronic, hybrid and strange stars with maximum masses above $2 M_{⊙}$ and show that the frequency of the $p_{1}$ and $g$ fluid modes contains key information about the internal composition of compact objects.
Comments:
Invited contribution to the EPJA Topical Issue "Exotic Matter in Neutron Stars", 11 pages, 6 figures
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1508.05548 [pdf]
EPJA(2016)·51 citations
16
[Submitted on 23 Aug 2015] (cross-list from hep-lat)
The sigma meson from lattice QCD with two-pion interpolating operators
Dean Howarth🇺🇸 · Joel Giedt🇺🇸
In this article we describe our studies of the sigma meson, f_0(500), using two-pion correlation functions. We use lattice quantum chromodynamics in the quenched approximation with so-called clover fermions. By working at unphysical pion masses we are able to identify a would-be resonance with mass less than $2 m_{π}$ , and then extrapolate to the physical point. We include the most important annihilation diagram, which is "partially disconnnected" or "single annihilation." Because this diagram is quite expensive to compute, we introduce a somewhat novel technique for the computation of all-to-all diagrams, based on momentum sources and a truncation in momentum space. In practice, we use only $p = 0$ modes, so the method reduces to wall sources. At the point where the mass of the pion takes its physical value, we find a resonance in the $0^{++}$ two-pion channel with a mass of approximately $609 \pm 80$ MeV, consistent with the expected properties of the sigma meson, given the approximations we are making.
Comments:
1+21 pages, 3 figures, various improvements to discussion, added explanatory appendices
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1508.05658 [pdf]
Int.J.Mod.Phys.C(2017)·14 citations
17
[Submitted on 24 Aug 2015] (cross-list from hep-ph)
$χ_{c J}$ Polarization in Polarized Proton-Proton Collisions at RHIC
Gouranga C. Nayak🇺🇸
We study inclusive $χ_{c J}$ production with definite polarizations in polarized proton-proton collisions at $s$ = 200 GeV and 500 GeV at RHIC by using non-relativistic QCD (NRQCD) color-octet mechanism. We present results of rapidity distribution of $χ_{c 0}$ , $χ_{c 1}$ and $χ_{c 2}$ production with specific polarizations in polarized p-p collisions at RHIC within the PHENIX detector acceptance range. We also present the corresponding results for the spin asymmetries.
Comments:
Final Version, Accepted for Publication in Phys. Part. Nucl. Lett., 25 pages latex, 15 .eps figures. arXiv admin note: substantial text overlap with arXiv:hep-ph/0509335
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1508.05850 [pdf]
Phys.Part.Nucl.Lett.(2017)·2 citations
18
[Submitted on 24 Aug 2015] (cross-list from hep-lat)
Unitary Limit of Two-Nucleon Interactions in Strong Magnetic Fields
William Detmold🇺🇸 · Kostas Orginos🇺🇸 · Assumpta Parreno🇪🇸 · Martin J. Savage🇺🇸 · Brian C. Tiburzi🇺🇸 · Silas R. Beane🇺🇸 · Emmanuel Chang🇺🇸
Two-nucleon systems are shown to exhibit large scattering lengths in strong magnetic fields at unphysical quark masses, and the trends toward the physical values indicate that such features may exist in nature. Lattice QCD calculations of the energies of one and two nucleons systems are performed at pion masses of $m_{π} \sim 450$ and 806 MeV in uniform, time-independent magnetic fields of strength {\bf B}| \sim 10^{19} $-$ 10^{20}$ Gauss to determine the response of these hadronic systems to large magnetic fields. Fields of this strength may exist inside magnetars and in peripheral relativistic heavy ion collisions, and the unitary behavior at large scattering lengths may have important consequences for these systems.
Comments:
Accepted journal version
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1508.05884 [pdf]
PRL(2016)·32 citations

Affiliations

first authorsco-authorsvia INSPIRE