8,495 research outputs found
Two exact properties of the perturbative expansion for the two-dimensional electron liquid with Rashba or Dresselhaus spin-orbit coupling
We have identified two useful exact properties of the perturbative expansion
for the case of a two-dimensional electron liquid with Rashba or Dresselhaus
spin-orbit interaction and in the absence of magnetic field. The results allow
us to draw interesting conclusions regarding the dependence of the exchange and
correlation energy and of the quasiparticle properties on the strength of the
spin-orbit coupling which are valid to all orders in the electron-electron
interaction.Comment: 6 pages, 1 figur
Universal finite size corrections and the central charge in non solvable Ising models
We investigate a non solvable two-dimensional ferromagnetic Ising model with
nearest neighbor plus weak finite range interactions of strength \lambda. We
rigorously establish one of the predictions of Conformal Field Theory (CFT),
namely the fact that at the critical temperature the finite size corrections to
the free energy are universal, in the sense that they are exactly independent
of the interaction. The corresponding central charge, defined in terms of the
coefficient of the first subleading term to the free energy, as proposed by
Affleck and Blote-Cardy-Nightingale, is constant and equal to 1/2 for all
0<\lambda<\lambda_0 and \lambda_0 a small but finite convergence radius. This
is one of the very few cases where the predictions of CFT can be rigorously
verified starting from a microscopic non solvable statistical model. The proof
uses a combination of rigorous renormalization group methods with a novel
partition function inequality, valid for ferromagnetic interactions.Comment: 43 pages, 1 figur
Exchange energy and generalized polarization in the presence of spin-orbit coupling in two dimensions
We discuss a general form of the exchange energy for a homogeneous system of
interacting electrons in two spatial dimensions which is particularly suited in
the presence of a generic spin-orbit interaction. The theory is best formulated
in terms of a generalized fractional electronic polarization. Remarkably we
find that a net generalized polarization does not necessarily translate into an
increase in the magnitude of the exchange energy, a fact that in turn favors
unpolarized states. Our results account qualitatively for the findings of
recent experimental investigations
Fluctuation Relation beyond Linear Response Theory
The Fluctuation Relation (FR) is an asymptotic result on the distribution of
certain observables averaged over time intervals T as T goes to infinity and it
is a generalization of the fluctuation--dissipation theorem to far from
equilibrium systems in a steady state which reduces to the usual Green-Kubo
(GK) relation in the limit of small external non conservative forces. FR is a
theorem for smooth uniformly hyperbolic systems, and it is assumed to be true
in all dissipative ``chaotic enough'' systems in a steady state. In this paper
we develop a theory of finite time corrections to FR, needed to compare the
asymptotic prediction of FR with numerical observations, which necessarily
involve fluctuations of observables averaged over finite time intervals T. We
perform a numerical test of FR in two cases in which non Gaussian fluctuations
are observable while GK does not apply and we get a non trivial verification of
FR that is independent of and different from linear response theory. Our
results are compatible with the theory of finite time corrections to FR, while
FR would be observably violated, well within the precision of our experiments,
if such corrections were neglected.Comment: Version accepted for publication on the Journal of Statistical
Physics; minor changes; two references adde
The many facets of the (non relativistic) Nuclear Equation of State
A nucleus is a quantum many body system made of strongly interacting
Fermions, protons and neutrons (nucleons). This produces a rich Nuclear
Equation of State whose knowledge is crucial to our understanding of the
composition and evolution of celestial objects. The nuclear equation of state
displays many different features; first neutrons and protons might be treated
as identical particles or nucleons, but when the differences between protons
and neutrons are spelled out, we can have completely different scenarios, just
by changing slightly their interactions. At zero temperature and for neutron
rich matter, a quantum liquid gas phase transition at low densities or a
quark-gluon plasma at high densities might occur. Furthermore, the large
binding energy of the particle, a Boson, might also open the
possibility of studying a system made of a mixture of Bosons and Fermions,
which adds to the open problems of the nuclear equation of state.Comment: 71 pages, 30 figures, accepted by Prog. Part. Nucl. Phys. and in
pres
Fermi liquid behavior in the 2D Hubbard model at low temperatures
We prove that the weak coupling 2D Hubbard model away from half filling is a
Landau Fermi liquid up to exponentially small temperatures. In particular we
show that the wave function renormalization is an order 1 constant and
essentially temperature independent in the considered range of temperatures and
that the interacting Fermi surface is a regular convex curve. This result is
obtained by deriving a convergent expansion (which is not a power series) for
the two point Schwinger function by Renormalization Group methods and proving
at each order suitable power counting improvements due to the convexity of the
interacting Fermi surface. Convergence follows from determinant bounds for the
fermionic expectations.Comment: 66 pages, 10 figure
Are direct search experiments sensitive to all spin-independent WIMP candidates?
The common analysis of direct searches for spin-independent Weakly
Interacting Massive Particles (WIMPs) assumes that a spin-independent WIMP
couples with the same strength with both nucleons, \textit{i.e.} that the
spin-independent interaction is also fully isospin-independent. Though in a
fully isospin-dependent interaction scenario the spin-independent WIMP-nucleus
cross section is strongly quenched, the leading experiments are still sensitive
enough to set limits 1-2 orders of magnitude less stringent than those
traditionally presented. In the isospin-dependent scenario the difference
between the limits of CDMS-II and ZEPLIN-I is significantly reduced. Here, a
model-independent framework is discussed and applied to obtain the current
general model-independent limits.Comment: 4 pages, 4 figures, revtex4.0, submitted to Phys. Rev. Let
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