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A. Bulgac

Publications and source records attributed to A. Bulgac.

24 records · Page 2Linked to original sources
arXiv2011

UNEDF: Advanced Scientific Computing Transforms the Low-Energy Nuclear Many-Body Problem

The UNEDF SciDAC collaboration of nuclear theorists, applied mathematicians, and computer scientists is developing a comprehensive description of nuclei and their reactions that delivers maximum predictive power with quantified uncertainties. This paper illustrates significant milestones accomplished by UNEDF through integration of the theoretical approaches, advanced numerical algorithms, and leadership class computational resources.

physics.comp-ph↗
arXiv2009

The Finite Temperature Pairing Gap of a Unitary Fermi Gas by Quantum Monte Carlo Calculations

We calculate the one-body temperature Green's (Matsubara) function of the unitary Fermi gas via Quantum Monte Carlo, and extract the spectral weight function $A(p,ω)$ using the methods of maximum entropy and singular value decomposition. From $A(p,ω)$ we determine the quasiparticle spectrum, which can be accurately parametrized by three functions of temperature: an effective mass $m^*$, a mean-field potential $U$, and a gap $Δ$. Below the critical temperature $T_c=0.15\varepsilon_F$ the results for $m^*$, $U$ and $Δ$ can be accurately reproduced using an independent quasiparticle model. We find evidence of a pseudogap in the fermionic excitation spectrum for temperatures up to {$T^*\approx 0.20\varepsilon_{F} > T_c$}.

cond-mat.stat-mech↗
arXiv2004

Scaling theory of excitations in trapped fermionic condensates

Formulas are derived for the coupled quadrupolar and monopolar oscillations of a fermion condensate trapped in a axially symmetric harmonic potential. We consider two-component condensates with a large particle-particle scattering length and in the limits of frequencies either small (adiabatic) or large (diabatic) compared to the pairing gap. Using the method of coordinate scaling, we reproduce Stringari's results for adiabatic excitations and present new results for the diabatic limit. Unlike the adiabatic oscillations, the diabatic ones show sensitivity to the interaction between particles.

physics.atom-ph↗
arXiv1996

Quantum Diffusion and Tunneling with Parametric Banded Random Matrix Hamiltonians

The microscopic origin of dissipation of a driven quantum many body system is addressed in the framework of a parametric banded random matrix approach. We find noticeable violations of the fluctuation-dissipation theorem and we observe also that the energy diffusion has a markedly non-Gaussian character. Within the Feynman-Vernon path integral formalism and in the Markovian limit, we further consider the time evolution of a slow subsystem coupled to such a ``bath'' of intrinsic degrees of freedom. We show that dissipation leads to qualitative modifications of the time evolution of the density matrix of the slow subsystem. In either the spatial, momentum or energy representation the density distribution acquires very long tails and tunneling is greatly enhanced.

nucl-th↗