14,804 research outputs found
Unitary equilibrations: probability distribution of the Loschmidt echo
Closed quantum systems evolve unitarily and therefore cannot converge in a
strong sense to an equilibrium state starting out from a generic pure state.
Nevertheless for large system size one observes temporal typicality. Namely,
for the overwhelming majority of the time instants, the statistics of
observables is practically indistinguishable from an effective equilibrium one.
In this paper we consider the Loschmidt echo (LE) to study this sort of unitary
equilibration after a quench. We draw several conclusions on general grounds
and on the basis of an exactly-solvable example of a quasi-free system. In
particular we focus on the whole probability distribution of observing a given
value of the LE after waiting a long time. Depending on the interplay between
the initial state and the quench Hamiltonian, we find different regimes
reflecting different equilibration dynamics. When the perturbation is small and
the system is away from criticality the probability distribution is Gaussian.
However close to criticality the distribution function approaches a double
peaked, "batman-hood" shaped, universal form.Comment: 15 pages, 16 figure
Cosmic ray production in modified gravity
This paper is a reply to the criticism of our work on particle production in
modified gravity by D. Gorbunov and A. Tokareva. We show that their arguments
against efficient particle production are invalid. theories can lead to
an efficient generation of high energy cosmic rays in contracting systems.Comment: In response to criticism by referees several clarifying comments are
added. The results of the paper remain largely unchanged. Version to appear
on EPJ
Conformal Truncation of Chern-Simons Theory at Large
We set up and analyze the lightcone Hamiltonian for an abelian Chern-Simons
field coupled to fermions in the limit of large using conformal
truncation, i.e. with a truncated space of states corresponding to primary
operators with dimension below a maximum cutoff . In both the
Chern-Simons theory, and in the model at infinite , we compute the
current spectral functions analytically as a function of and
reproduce previous results in the limit that the truncation
is taken to . Along the way, we determine how to preserve gauge
invariance and how to choose an optimal discrete basis for the momenta of
states in the truncation space.Comment: 32+25 pages, 8 figures. v2: updated ref
Duo: a general program for calculating spectra of diatomic molecules
Duo is a general, user-friendly program for computing rotational,
rovibrational and rovibronic spectra of diatomic molecules. Duo solves the
Schr\"{o}dinger equation for the motion of the nuclei not only for the simple
case of uncoupled, isolated electronic states (typical for the ground state of
closed-shell diatomics) but also for the general case of an arbitrary number
and type of couplings between electronic states (typical for open-shell
diatomics and excited states). Possible couplings include spin-orbit, angular
momenta, spin-rotational and spin-spin. Corrections due to non-adiabatic
effects can be accounted for by introducing the relevant couplings using
so-called Born-Oppenheimer breakdown curves.
Duo requires user-specified potential energy curves and, if relevant, dipole
moment, coupling and correction curves. From these it computes energy levels,
line positions and line intensities. Several analytic forms plus interpolation
and extrapolation options are available for representation of the curves. Duo
can refine potential energy and coupling curves to best reproduce reference
data such as experimental energy levels or line positions. Duo is provided as a
Fortran 2003 program and has been tested under a variety of operating systems
Recommended from our members
Pension schemes versus real estate
The demographic, economic and social changes that have characterized the last decades, and the dramatic financial crisis that has taken place since 2008, have led to a demand for structural changes in the pension sector and a growing interest in individual pension products. Hence the need, for most elderly people, to liquidate their fixed assets, which are usually the homes in which they live. This highlights products such as reverse mortgages and domestic reversibility plans. Within this context, we propose a contractual scheme where an immediate life annuity is obtained by paying a single-premium in the form of real estate rights (RERs), for example by transferring to an insurer the property title of a house or a similar realty, while keeping its usufruct or a restricted bundle of rights. The level of the installments depends on the fair value of the transferred RER at the contract’s issue, the life expectancy of the insured and the expected growth rate of the real estate market value. The contract design is developed by considering the control of the financial risk inherent in the contract itself, because of the prospective changes in the value of the RERs, and the level of the insurer’s leverage. Finally, we provide some numerical evidence of the proposed contractual structure, in order to compare the level of the installments according to the house return forecasts in different European countries
Relaxation time spectrum of low-energy excitations in one- and two-dimensional materials with charge or spin density waves
The long-time thermal relaxation of (TMTTF)Br, SrCuO
and SrCaCuO single crystals at temperatures below 1 K
and magnetic field up to 10 T is investigated. The data allow us to determine
the relaxation time spectrum of the low energy excitations caused by the
charge-density wave (CDW) or spin-density wave (SDW). The relaxation time is
mainly determined by a thermal activated process for all investigated
materials. The maximum relaxation time increases with increasing magnetic
field. The distribution of barrier heights corresponds to one or two Gaussian
functions. The doping of SrCaCuO with Ca leads to
a drastic shift of the relaxation time spectrum to longer time. The maximum
relaxation time changes from 50 s (x = 0) to 3000 s (x = 12) at 0.1 K and 10 T.
The observed thermal relaxation at x=12 clearly indicates the formation of the
SDW ground state at low temperatures
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