Nuclear Theory·nucl-th

Wednesday·August 19, 2015

10 papers—3 primary·7 cross-listed

01
Present status of coupled-channels calculations for heavy-ion subbarrier fusion reactions
K. Hagino · J.M. Yao
The coupled-channels method has been a standard tool in analyzing heavy-ion fusion reactions at energies around the Coulomb barrier. We investigate three simplifications usually adopted in the coupled-channels calculations. These are i) the exclusion of non-collective excitations, ii) the assumption of coordinate independent coupling strengths, and iii) the harmonic oscillator approximation for multi-phonon excitations. In connection to the last point, we propose a novel microscopic method based on the beyond-mean-field approach in order to take into account the anharmonic effects of collective vibrations.
nucl-thnucl-exEPJ Web Conf.(2016)·2 citations
02
Inhomogeneous chiral symmetry breaking in dense neutron-star matter
Michael Buballa🇩🇪 · Stefano Carignano🇩🇪
An increasing number of model results suggests that chiral symmetry is broken inhomogeneously in a certain window at intermediate densities in the QCD phase diagram. This could have significant effects on the properties of compact stars, possibly leading to new astrophysical signatures. In this contribution we discuss this idea by reviewing recent results on inhomogeneous chiral symmetry breaking under an astrophysics-oriented perspective. After introducing two commonly studied spatial modulations of the chiral condensate, the chiral density wave and the real kink crystal, we focus on their properties and their effect on the equation of state of quark matter. We also describe how these crystalline phases are affected by different elements which are required for a realistic description of a compact star, such as charge neutrality, the presence of magnetic fields, vector interactions and the interplay with color-superconductivity. Finally, we discuss possible signatures of inhomogeneous chiral symmetry breaking in the core of compact stars, considering the cases of mass-radius relations and neutrino emissivity explicitly.
nucl-thastro-ph.HEhep-phEPJA(2016)·50 citations
03
Deviations of the Energy-Momentum Tensor from Equilibrium in the Initial State for Hydrodynamics from Transport Approaches
Dmytro Oliinychenko🇩🇪 · Hannah Petersen🇩🇪
Many hybrid models of heavy ion collisions construct the initial state for hydrodynamics from transport models. Hydrodynamics requires that the energy-momentum tensor $T^{μν}$ and four-currents $j^{μ}$ do not deviate considerably from the equilibrium ideal-fluid form, but the ones constructed from transport do not necessarily possess this property. In this work we investigate the space-time picture of $T^{μν}$ deviations from equilibrium in Au+Au collisions using a coarse-grained transport approach. The collision energy is varied in the range $E_{l ab} = 5 - 160 A$ GeV. The sensitivity of $T^{μν}$ deviations from equilibrium to collision centrality, and other parameters such as the switching criterion, the amount of statistics used to construct the initial state, and the smearing parameter $σ$ is investigated. For low statistics deviations of $T^{μν}$ from equilibrium are large and dominated by the effect of finite sampling. For large statistics the pressure anisotropy plays the most significant role, while the off-diagonal components of $T^{μν}$ are small in a large volume during the whole evolution. For all considered energies and centralities the pressure anisotropy exhibits a similar feature: there is a narrow interval of time, when it rapidly drops in a considerable volume. This allows us to introduce an "isotropization time," which is found to decrease with energy and slightly increase with centrality. The isotropization times are larger than times typically used for initializing hydrodynamics.
nucl-thhep-phPRC(2016)·57 citations
04
Hard Matching for Boosted Tops at Two Loops
Andre H. Hoang🇦🇹 · Aditya Pathak🇺🇸 · Piotr Pietrulewicz🇩🇪 · Iain W. Stewart🇺🇸
Cross sections for top quarks provide very interesting physics opportunities, being both sensitive to new physics and also perturbatively tractable due to the large top quark mass. Rigorous factorization theorems for top cross sections can be derived in several kinematic scenarios, including the boosted regime in the peak region that we consider here. In the context of the corresponding factorization theorem for $e^{+} e^{-}$ collisions we extract the last missing ingredient that is needed to evaluate the cross section differential in the jet-mass at two-loop order, namely the matching coefficient at the scale $μ ≃ m_{t}$ . Our extraction also yields the final ingredients needed to carry out logarithmic resummation at next-to-next-to-leading logarithmic order (or N $^{3}$ LL if we ignore the missing 4-loop cusp anomalous dimension). This coefficient exhibits an amplitude level rapidity logarithm starting at $O (α_{s}^{2})$ due to virtual top quark loops, which we treat using rapidity renormalization group (RG) evolution. Interestingly, this rapidity RG evolution appears in the matching coefficient between two effective theories around the heavy quark mass scale $μ ≃ m_{t}$ .
↳ hep-phnucl-thJHEP(2015)·52 citations
05
Finite Volume Corrections to the Electromagnetic Mass of Composite Particles
Jong-Wan Lee🇺🇸 · Brian C. Tiburzi🇺🇸
The long-range electromagnetic interaction presents a challenge for numerical computations in QCD + QED. In addition to power-law finite volume effects, the standard lattice gauge theory approach introduces non-locality through removal of photon zero-momentum modes. The resulting finite volume effects must be quantitatively understood; and, to this end, non-relativistic effective field theories are an efficient tool, especially in the case of composite particles. Recently an oddity related to non-locality of the standard lattice approach was uncovered by the Budapest-Marseille-Wuppertal collaboration. Explicit contributions from antiparticles appear to be required so that finite volume QED results for a point-like fermion can be reproduced in the effective field theory description. We provide transparency for this argument by considering point-like scalars and spinors in finite volume QED using the method of regions. For the more germane case of composite particles, we determine that antiparticle modes contribute to the finite-volume electromagnetic mass of composite spinors through terms proportional to the squares of time-like form factors evaluated at threshold. We extend existing finite volume calculations to one order higher, which is particularly relevant for the electromagnetic mass of light nuclei. Additionally, we verify that the analogous finite volume contributions to the nucleon mass in chiral perturbation theory vanish in accordance with locality.
↳ hep-lathep-phnucl-thPRD(2016)·15 citations
06
Composite Fermions and the First-Landau-Level Fine Structure of the Fractional Quantum Hall Effect
W. C. Haxton · Daniel J. Haxton
A set of scalar operators are employed to generate explicit representations of both hierarchy states (e.g., the series of fillings 1/3, 2/5, 3/7, ... ) and their conjugates (fillings 1, 2/3, 3/5, ...) as non-interacting quasi-electrons filling fine-structure sub-shells within the FLL. This yields, for planar and spherical geometries, a quasi-electron representation of the incompressible FLL state of filling p/(2p +1) in a magnetic field of strength B that is algebraically identical to the IQHE state of filling p in a magnetic field of strength B/(2p+1). The construction provides a precise definition of the quasi-electron/composite fermion that differs in some respects from common descriptions: they are eigenstates of L,Lz; they and the FLL subshells they occupy carry a third index I that is associated with breaking of scalar pairs; they absorb in their internal wave functions one, not two, units of magnetic flux; and they share a common, simple structure as vector products of a spinor creating an electron and one creating magnetic flux. We argue that these properties are a consequence of the breaking of the degeneracy of noninteracting electrons within the FLL by the scale-invariant Coulomb potential. We discuss the sense in which the wave function construction supports basic ideas of both composite fermion and hierarchical descriptions of the FQHE. We describe symmetries of the quasi-electrons at half filling, where a deep Fermi sea of quasi-electrons forms, and the quasi-electrons take on Majorana and pseudo-Dirac characters. Finally, we show that the wave functions can be viewed as fermionic excitations of the bosonic half-filled shell, producing at half filling an operator that differs from but plays the same role as the Pfaffian.
↳ cond-mat.str-elnucl-thphysics.chem-phPRB(2016)·3 citations
07
Vector meson spectral function and dilepton rate in an effective mean field model
Chowdhury Aminul Islam🇮🇳 · Sarbani Majumder🇮🇳 · Najmul Haque🇺🇸 · Munshi G. Mustafa🇮🇳
We have studied the vector meson spectral function (VMSF) in a hot and dense medium within an effective QCD model namely the Nambu-Jona-Lasinio (NJL) and its Polyakov Loop extended version (PNJL) with and without the effect of isoscalar vector interaction (IVI). The effect of the IVI has been taken into account using the ring approximation. We obtained the dilepton production rate (DPR) using the VMSF and observed that at moderate temperature it is enhanced in the PNJL model as compared to the NJL and Born rate due to the suppression of color degrees of freedom.
↳ hep-phnucl-thSpringer Proc.Phys.(2016)·0 citations
08
Three-loop HTLpt thermodynamics at finite temperature and chemical potential
Aritra Bandyopadhyay🇮🇳 · Najmul Haque🇺🇸 · Munshi G. Mustafa🇮🇳 · Michael Strickland🇺🇸 · Nan Su🇩🇪
In this proceedings we present a state-of-the-art method of calculating thermodynamic potential at finite temperature and finite chemical potential, using Hard Thermal Loop perturbation theory (HTLpt) up to next-to-next-leading-order (NNLO). The resulting thermodynamic potential enables us to evaluate different thermodynamic quantities including pressure and various quark number susceptibilities (QNS). Comparison between our analytic results for those thermodynamic quantities with the available lattice data shows a good agreement.
↳ hep-phnucl-thSpringer Proc.Phys.(2016)·0 citations
09
Quark model with chiral-symmetry breaking and confinement in the Covariant Spectator Theory
Elmar P. Biernat🇵🇹 · M. T. Peña🇵🇹 · J. E. Ribeiro🇵🇹 · A. Stadler🇵🇹 · F. Gross🇺🇸
We propose a model for the quark-antiquark interaction in Minkowski space using the Covariant Spectator Theory. We show that with an equal-weighted scalar-pseudoscalar structure for the confining part of our interaction kernel the axial-vector Ward-Takahashi identity is preserved and our model complies with the Adler-zero constraint for pi-pi-scattering imposed by chiral symmetry.
↳ hep-phnucl-thEPJ Web Conf.(2016)·1 citation
10
Phenomenological neutron star equations of state: 3-window modeling of QCD matter
Toru Kojo🇺🇸
We discuss the 3-window modeling of cold, dense QCD matter equations of state at density relevant to neutron star properties. At low baryon density, n_B < ~ 2n_s (n_s: nuclear saturation density), we utilize purely hadronic equations of state that are constrained by empirical observations at density n_B ~ n_s and neutron star radii. At high density, n_B > ~ 5n_s, we use the percolated quark matter equations of state which must be very stiff to pass the two-solar mass constraints. The intermediate domain at 2 < n_B/n_s < 5 is described as neither purely hadronic nor percolated quark matter, and the equations of state are inferred by interpolating hadronic and percolated quark matter equations of state. Possible forms of the interpolation are severely restricted by the condition on the (square of) speed of sound, 0 < c_s^2 < 1. The characteristics of the 3-window equation of state are compared with those of conventional hybrid and self-bound quark matters. Using a schematic quark model for the percolated domain, it is argued that the two-solar mass constraint requires the model parameters to be as large as their vacuum values, indicating that the gluon dynamics remains strongly non-perturbative to n_B ~ 10n_s. The hyperon puzzle is also briefly discussed in light of quark descriptions.
↳ hep-phastro-ph.HEnucl-thEPJA(2016)·45 citations

Affiliations

first authorsco-authorsvia INSPIRE