28,795 research outputs found
Equation of state of non-relativistic matter from automated perturbation theory and complex Langevin
We calculate the pressure and density of polarized non-relativistic systems
of two-component fermions coupled via a contact interaction at finite
temperature. For the unpolarized one-dimensional system with an attractive
interaction, we perform a third-order lattice perturbation theory calculation
and assess its convergence by comparing with hybrid Monte Carlo. In that
regime, we also demonstrate agreement with real Langevin. For the repulsive
unpolarized one-dimensional system, where there is a so-called complex phase
problem, we present lattice perturbation theory as well as complex Langevin
calculations. For our studies, we employ a Hubbard-Stratonovich transformation
to decouple the interaction and automate the application of Wick's theorem for
perturbative calculations, which generates the diagrammatic expansion at any
order. We find excellent agreement between the results from our perturbative
calculations and stochastic studies in the weakly interacting regime. In
addition, we show predictions for the strong coupling regime as well as for the
polarized one-dimensional system. Finally, we show a first estimate for the
equation of state in three dimensions where we focus on the polarized unitary
Fermi gas.Comment: 8 pages, 6 figures, proceedings of Lattice2017, Granada, Spai
Creation of Entanglement by Interaction with a Common Heat Bath
I show that entanglement between two qubits can be generated if the two
qubits interact with a common heat bath in thermal equilibrium, but do not
interact directly with each other. In most situations the entanglement is
created for a very short time after the interaction with the heat bath is
switched on, but depending on system, coupling, and heat bath, the entanglement
may persist for arbitrarily long times. This mechanism sheds new light on the
creation of entanglement. A particular example of two quantum dots in a closed
cavity is discussed, where the heat bath is given by the blackbody radiation.Comment: 4 revtex pages, 1 eps figure; replaced with published version; short
discussion on entanglement distillation adde
Three Generations on the Quintic Quotient
A three-generation SU(5) GUT, that is 3x(10+5bar) and a single 5-5bar pair,
is constructed by compactification of the E_8 heterotic string. The base
manifold is the Z_5 x Z_5-quotient of the quintic, and the vector bundle is the
quotient of a positive monad. The group action on the monad and its
bundle-valued cohomology is discussed in detail, including topological
restrictions on the existence of equivariant structures. This model and a
single Z_5 quotient are the complete list of three generation quotients of
positive monads on the quintic.Comment: 19 pages, LaTeX. v2: section on anomaly cancellation adde
Thermal equation of state of polarized fermions in one dimension via complex chemical potentials
We present a nonperturbative computation of the equation of state of
polarized, attractively interacting, nonrelativistic fermions in one spatial
dimension at finite temperature. We show results for the density, spin
magnetization, magnetic susceptibility, and Tan's contact. We compare with the
second-order virial expansion, a next-to-leading-order lattice perturbation
theory calculation, and interpret our results in terms of pairing correlations.
Our lattice Monte Carlo calculations implement an imaginary chemical potential
difference to avoid the sign problem. The thermodynamic results on the
imaginary side are analytically continued to obtain results on the real axis.
We focus on an intermediate- to strong-coupling regime, and cover a wide range
of temperatures and spin imbalances.Comment: 14 pages, 19 figures; published versio
Hadron-nucleus scattering in the local reggeon model with pomeron loops for realistic nuclei
Contribution of simplest loops for hadron-nucleus scattering cross-sections
is studied in the Local Reggeon Field Theory with a supercritical pomeron. It
is shown that inside the nucleus the supercritical pomeron transforms into a
subcritical one, so that perturbative treatment becomes possible. The pomeron
intercept becomes complex, which leads to oscillations in the cross-sections.Comment: 13 pages, 6 figure
Surmounting the sign problem in non-relativistic calculations: a case study with mass-imbalanced fermions
The calculation of the ground state and thermodynamics of mass-imbalanced
Fermi systems is a challenging many-body problem. Even in one spatial
dimension, analytic solutions are limited to special configurations and
numerical progress with standard Monte Carlo approaches is hindered by the sign
problem. The focus of the present work is on the further development of methods
to study imbalanced systems in a fully non-perturbative fashion. We report our
calculations of the ground-state energy of mass-imbalanced fermions using two
different approaches which are also very popular in the context of the theory
of the strong interaction (Quantum Chromodynamics, QCD): (a) the hybrid Monte
Carlo algorithm with imaginary mass imbalance, followed by an analytic
continuation to the real axis; and (b) the Complex Langevin algorithm. We cover
a range of on-site interaction strengths that includes strongly attractive as
well as strongly repulsive cases which we verify with non-perturbative
renormalization group methods and perturbation theory. Our findings indicate
that, for strong repulsive couplings, the energy starts to flatten out,
implying interesting consequences for short-range and high-frequency
correlation functions. Overall, our results clearly indicate that the Complex
Langevin approach is very versatile and works very well for imbalanced Fermi
gases with both attractive and repulsive interactions.Comment: 11 pages, 5 figure
Faraday-rotation fluctuation spectroscopy with static and oscillating magnetic fields
By Faraday-rotation fluctuation spectroscopy one measures the spin noise via
Faraday-induced fluctuations of the polarization plane of a laser transmitting
the sample. In the fist part of this paper, we present a theoretical model of
recent experiments on alkali gas vapors and semiconductors, done in the
presence of a {\em static} magnetic field. In a static field, the spin noise
shows a resonance line, revealing the Larmor frequency and the spin coherence
time of the electrons. Second, we discuss the possibility to use an {\em
oscillating} magnetic field in the Faraday setup. With an oscillating field
applied, one can observe multi-photon absorption processes in the spin noise.
Furthermore an oscillating field could also help to avoid line broadening due
to structural or chemical inhomogeneities in the sample, and thereby increase
the precision of the spin-coherence time measurement.Comment: 5 pages, 7 figure
Documentation of the Analyses of the Benefits and Costs of Aeronautical Research and Technology models (ABC-ART). Volume 2: Appendices
Fleet variables are defined, and source codes for each module are presented
Documentation of the analysis of the benefits and costs of aeronautical research and technology models, volume 1
The analysis of the benefits and costs of aeronautical research and technology (ABC-ART) models are documented. These models were developed by NASA for use in analyzing the economic feasibility of applying advanced aeronautical technology to future civil aircraft. The methodology is composed of three major modules: fleet accounting module, airframe manufacturing module, and air carrier module. The fleet accounting module is used to estimate the number of new aircraft required as a function of time to meet demand. This estimation is based primarily upon the expected retirement age of existing aircraft and the expected change in revenue passenger miles demanded. Fuel consumption estimates are also generated by this module. The airframe manufacturer module is used to analyze the feasibility of the manufacturing the new aircraft demanded. The module includes logic for production scheduling and estimating manufacturing costs. For a series of aircraft selling prices, a cash flow analysis is performed and a rate of return on investment is calculated. The air carrier module provides a tool for analyzing the financial feasibility of an airline purchasing and operating the new aircraft. This module includes a methodology for computing the air carrier direct and indirect operating costs, performing a cash flow analysis, and estimating the internal rate of return on investment for a set of aircraft purchase prices
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