Nuclear Theory·nucl-th

Tuesday·June 23, 2015

14 papers—8 primary·6 cross-listed

01
Baryon mass splittings and strong CP violation in SU(3) Chiral Perturbation Theory
Jordy de Vries🇩🇪 · Emanuele Mereghetti🇺🇸 · Andre Walker-Loud🇺🇸
We study $S U (3)$ flavor-breaking corrections to the relation between the octet baryon masses and the nucleon-meson CP-violating interactions induced by the QCD $θ ˉ$ term. We work within the framework of $S U (3)$ chiral perturbation theory and work through next-to-next-to-leading order in the $S U (3)$ chiral expansion, which is $O (m_{q}^{2})$ . At lowest order, the CP-odd couplings induced by the QCD $θ ˉ$ term are determined by mass splittings of the baryon octet, the classic result of Crewther et al. We show that for each isospin-invariant CP-violating nucleon-meson interaction there exists one relation which is respected by loop corrections up to the order we work, while other leading-order relations are violated. With these relations we extract a precise value of the pion-nucleon coupling $g ˉ_{0}$ by using recent lattice QCD evaluations of the proton-neutron mass splitting. In addition, we derive semi-precise values for CP-violating coupling constants between heavier mesons and nucleons with $\sim 30%$ uncertainty and discuss their phenomenological impact on electric dipole moments of nucleons and nuclei.
nucl-thhep-lathep-phPRC(2015)·96 citations
02
The Low-Energy Quadrupole Mode of Nuclei
S. Frauendorf
The phenomenological classification of collective quadrupole excitations by means of the Bohr Hamiltonian is reviewed with focus on signatures for triaxility. The variants of the microscopic Bohr Hamiltonian derived by means of the Adiabatic Time Dependent Mean Field theory from the Pairing plus Quadrupole-Quadrupole interaction, the Shell Correction Method, the Skyrme Energy Density Functional, the Relativistic Mean Field Theory, and the Gogny interaction are discussed and applications to concrete nuclides reviewed. The Generator Coordinate Method for the five dimensional quadrupole deformation space and first applications to triaxial nuclei are presented. The phenomenological classification in the framework of the Interacting Boson Model is discussed with a critical view on the boson number counting rule. The recent success in calculating the model parameters by mapping the mean field deformation energy surface on the bosonic one is discussed and the applications listed. A critical assessment of the models is given with focus on the limitations due to the adiabatic approximation. The Tidal Wave approach and the Triaxial Projected Shell Model are presented as practical approaches to calculate spectral properties outside the adiabatic region.
nucl-thIJMPE(2015)·29 citations
03
Reassessing nuclear matter incompressibility and its density dependence
J. N. De · S. K. Samaddar · B. K. Agrawal
Experimental giant monopole resonance energies are now known to constrain nuclear incompressibility of symmetric nuclear matter $K$ and its density slope $M$ at a particular value of sub-saturation density, the crossing density $ρ_{c}$ . Consistent with these constraints, we propose a reasonable way to construct a plausible equation of state of symmetric nuclear matter in a broad density region around the saturation density $ρ_{0}$ . Help of two additional empirical inputs, the value of $ρ_{0}$ and that of the energy per nucleon $e (ρ_{0})$ are needed. The value of $K (ρ_{0})$ comes out to be $211.9 \pm 24.5$ MeV.
nucl-thPRC(2015)·20 citations
04
Neutron star structure in an in-medium modified chiral soliton model
Ulugbek Yakhshiev🇰🇷
We study the internal structure of a static and spherically symmetric neutron star in the framework of an in-medium modified chiral soliton model. The Equations of State describing an infinite and asymmetric nuclear matter are obtained introducing the density dependent functions into the low energy free space Lagrangian of the model starting from the phenomenology of pionic atoms. The parametrizations of density dependent functions are related to the properties of isospin asymmetric nuclear systems at saturation density of symmetric nuclear matter $ρ_{0} ≃ 0.16$ ~fm $^{- 3}$ . Our results, corresponding to the compressibility of symmetric nuclear matter in the range $250 \mbox M e V \leq K_{0} \leq 270 \mbox M e V$ and the slop parameter value of symmetry energy in the range $30 \mbox M e V \leq L_{S} \leq 50 \mbox M e V$ , are consistent with the results from other approaches and with the experimental indications. Using the modified Equations of State, near the saturation density of symmetric nuclear matter $ρ_{0}$ , the extrapolations to the high density and highly isospin asymmetric regions have been performed. The calculations showed that the properties of $\sim 1.4 M_{⊙}$ and $\sim 2 M_{⊙}$ neutron stars can be well reproduced in the framework of present approach.
nucl-thhep-phPLB(2015)·6 citations
05
Mapping the Generator Coordinate Method to the Coupled Cluster Approach
Jason L. Stuber
The generator coordinate method (GCM) casts the wavefunction as an integral over a weighted set of non-orthogonal single determinantal states. In principle this representation can be used like the configuration interaction (CI) or shell model to systematically improve the approximate wavefunction towards an exact solution. In practice applications have generally been limited to systems with less than three degrees of freedom. This bottleneck is directly linked to the exponential computational expense associated with the numerical projection of broken symmetry Hartree-Fock (HF) or Hartree-Fock-Bogoliubov (HFB) wavefunctions and to the use of a variational rather than a bi-variational expression for the energy. We circumvent these issues by choosing a hole-particle representation for the generator and applying algebraic symmetry projection, via the use of tensor operators and the invariant mean (operator average). The resulting GCM formulation can be mapped directly to the coupled cluster (CC) approach, leading to a significantly more efficient approach than the conventional GCM route.
nucl-thcond-mat.str-elphysics.chem-ph0 citations
06
Partial dynamical symmetry in Bose-Fermi systems
P. Van Isacker (GANIL)🇫🇷 · J. Jolie🇩🇪 · T. Thomas🇩🇪 · A. Leviatan🇮🇱
We generalize the notion of partial dynamical symmetry (PDS) to a system of interacting bosons and fermions. In a PDS, selected states of the Hamiltonian are solvable and preserve the symmetry exactly, while other states are mixed. As a first example of such novel symmetry construction, spectral features of the odd-mass nucleus $^{195}$ Pt are analyzed.
nucl-thquant-phPRC(2015)·13 citations
07
Analytic Bjorken flow in one-dimensional relativistic magnetohydrodynamics
Victor Roy🇩🇪 · Shi Pu🇩🇪 · Luciano Rezzolla🇩🇪 · Dirk Rischke🇩🇪
In the initial stage of relativistic heavy-ion collisions, strong magnetic fields appear due to the large velocity of the colliding charges. The evolution of these fields appears as a novel and intriguing feature in the fluid-dynamical description of heavy-ion collisions. In this work, we study analytically the one-dimensional, longitudinally boost-invariant motion of an ideal fluid in the presence of a transverse magnetic field. Interestingly, we find that, in the limit of ideal magnetohydrodynamics, i.e., for infinite conductivity, and irrespective of the strength of the initial magnetization, the decay of the fluid energy density $e$ with proper time $τ$ is the same as for the time-honored "Bjorken flow" without magnetic field. Furthermore, when the magnetic field is assumed to decay $\sim τ^{- a}$ , where $a$ is an arbitrary number, two classes of analytic solutions can be found depending on whether $a$ is larger or smaller than one. In summary, the analytic solutions presented here highlight that the Bjorken flow is far more general than formerly thought. These solutions can serve both to gain insight on the dynamics of heavy-ion collisions in the presence of strong magnetic fields and as testbeds for numerical codes.
nucl-thastro-ph.HEgr-qchep-phPLB(2015)·136 citations
08
Alpha Cluster Model of Atomic Nuclei
Zbigniew Sosin🇵🇱 · Jan Błocki🇵🇱 · Jinesh Kallunkathariyil🇵🇱 · Jerzy Łukasik🇵🇱 · Piotr Pawłowski🇵🇱
Description of a nuclear system in its ground state and at low excitations based on the equation of state (EoS) around normal density is presented. In the expansion of the EoS around the saturation point additional spin polarization terms are taken into account. These terms, together with the standard symmetry term, are responsible for appearance of the $α$ -like clusters in the ground state configurations of the N=Z even-even nuclei. At the nuclear surface these clusters can be identified as alpha particles. A correction for the surface effects is introduced for atomic nuclei. Taking into account an additional interaction between clusters the binding energies and sizes of the considered nuclei are very accurately described. The limits of the EoS parameters are established from the properties of the $α$ , $^{3}$ He and $t$ particles.
nucl-thEPJA(2016)·7 citations
09
On thermalization of a boost-invariant non Abelian plasma
L. Bellantuono🇮🇹 · P. Colangelo🇮🇹 · F. De Fazio🇮🇹 · F. Giannuzzi🇮🇹
Using a holographic method, we further investigate the relaxation towards the hydrodynamic regime of a boost-invariant non-Abelian plasma taken out-of-equilibrium. In the dual description, the system is driven out-of-equilibrium by boundary sourcing, a deformation of the boundary metric, as proposed by Chesler and Yaffe. The effects of several deformation profiles on the bulk geometry are investigated by the analysis of the corresponding solutions of the Einstein equations. The time of restoration of the hydrodynamic regime is investigated: setting the effective temperature of the system at the end of the boundary quenching to $T_{e f f} (τ^{*}) = 500$ MeV, the hydrodynamic regime is reached after a lapse of time of $O$ (1 fm/c).
↳ hep-phhep-thnucl-thJHEP(2015)·27 citations
10
Quasi-power laws in multiparticle production processes
Grzegorz Wilk🇵🇱 · Zbigniew Włodarczyk🇵🇱
We review the ubiquitous presence in multiparticle production processes of quasi-power law distributions (i.e., distributions following pure power laws for large values of the argument but remaining finite, usually exponential, for small values). Special emphasis is placed on the conjecture that this reflects the presence in the produced hadronic systems of some intrinsic fluctuations. If described by parameter q they form, together with the scale parameter $T$ ("temperature"), basis of Tsallis distribution, $f (X) \sim [1 - (1 - q) X / T]^{1/ (1 - q)}$ , frequently used to describe the relevant distributions (the X being usually a transverse momentum). We discuss the origin of such quasi-power law behavior based on our experience with the description of multiparticle production processes. In particular, we discuss Tsallis distribution with complex nonextensivity parameter q and argue that it is needed to describe log-oscillations as apparently observed in recent data on large momentum distributions in very high energy p-p collisions.
↳ hep-phcond-mat.stat-mechnucl-thChaos Solitons Fractals(2015)·14 citations
11
Quantum scalar fields in de Sitter space from the nonperturbative renormalization group
Maxime Guilleux🇫🇷 · Julien Serreau🇫🇷
We investigate scalar field theories in de Sitter space by means of nonperturbative renormalization group techniques. We compute the functional flow equation for the effective potential of O(N) theories in the local potential approximation and we study the onset of curvature-induced effects as quantum fluctuations are progressively integrated out from subhorizon to superhorizon scales. This results in a dimensional reduction of the original action to an effective zero-dimensional Euclidean theory. We show that the latter is equivalent both to the late-time equilibrium state of the stochastic approach of Starobinsky and Yokoyama and to the effective theory for the zero mode on Euclidean de Sitter space. We investigate the immediate consequences of this dimensional reduction: symmetry restoration and dynamical mass generation.
↳ hep-thgr-qchep-phnucl-thPRD(2015)·66 citations
12
Neutrino Quantum Kinetic Equations
Cristina Volpe🇫🇷
Neutrinos propagate in astrophysical and cosmological environments modifying their flavor in intriguing ways. The study of neutrino propagation in media is based on the mean-field, extended mean-field and Boltzmann equations. We summarise salient features of these evolution equations and the methods employed so far to derive them. We emphasize applications to situations of observational interest.
↳ astro-ph.SRhep-phnucl-thIJMPE(2015)·96 citations
13
Iso-vector and Iso-scalar Tensor Charges of the Nucleon from Lattice QCD
Tanmoy Bhattacharya🇺🇸 · Vincenzo Cirigliano🇺🇸 · Saul Cohen🇺🇸 · Rajan Gupta🇺🇸 · Anosh Joseph🇩🇪 · Huey-Wen Lin🇺🇸 · Boram Yoon🇺🇸
We present results for the iso-vector and flavor diagonal tensor charges $g_{T}^{u - d}$ , $g_{T}^{u}$ , $g_{T}^{d}$ , and $g_{T}^{s}$ needed to probe novel tensor interactions at the TeV scale in neutron and nuclear $β$ -decays and the contribution of the quark electric dipole moment (EDM) to the neutron EDM. The lattice QCD calculations were done using nine ensembles of gauge configurations generated by the MILC collaboration using the HISQ action with 2+1+1 dynamical flavors. These ensembles span three lattice spacings $a \approx 0.06, 0.09$ and $0.12$ fm and three quark masses corresponding to the pion masses $M_{π} \approx 130, 220$ and $310$ MeV. Using estimates from these ensembles, we quantify all systematic uncertainties and perform a simultaneous extrapolation in the lattice spacing, volume and light quark masses for the connected contributions. The final estimates of the connected nucleon (proton) tensor charge for the iso-vector combination is $g_{T}^{u - d} = 1.020 (76)$ in the $MS ˉ$ scheme at $2$ GeV. The additional disconnected quark loop contributions needed for the flavor-diagonal matrix elements are calculated using a stochastic estimator employing the truncated solver method with the all-mode-averaging technique. We find that the size of the disconnected contribution is smaller than the statistical error in the connected contribution. This allows us to bound the disconnected contribution and include it as an additional uncertainty in the flavor-diagonal charges. After a continuum extrapolation, we find $g_{T}^{u} = 0.774 (66)$ , $g_{T}^{d} = - 0.233 (28)$ and $g_{T}^{u + d} = 0.541 (67)$ . The strangeness tensor charge, that can make a significant contribution to the neutron EDM due to the large ratio $m_{s} / m_{u, d}$ , is $g_{T}^{s} = 0.008 (9)$ in the continuum limit.
↳ hep-lathep-phnucl-thPRD(2015)·169 citations
14
Isotropization and hydrodynamization in weakly coupled heavy-ion collisions
Aleksi Kurkela🇨🇭 · Yan Zhu🇪🇸
We numerically solve 2+1D effective kinetic theory of weak coupling QCD under longitudinal expansion relevant for early stages of heavy-ion collisions. We find agreement with viscous hydrodynamics and classical Yang-Mills simulations in the regimes where they are applicable. By choosing initial conditions that are motivated by color-glass-condensate framework we find that for Q=2GeV and $α_{s}$ =0.3 the system is approximately described by viscous hydrodynamics well before $τ ≲ 1.0$ fm/c.
↳ hep-phnucl-thPRL(2015)·314 citations

Affiliations

first authorsco-authorsvia INSPIRE