2,357 research outputs found
Effects of Bose-Einstein Condensation on forces among bodies sitting in a boson heat bath
We explore the consequences of Bose-Einstein condensation on
two-scalar-exchange mediated forces among bodies that sit in a boson gas. We
find that below the condensation temperature the range of the forces becomes
infinite while it is finite at temperatures above condensation.Comment: 10 pages, 2 figure
Interplay of electromagnetic noise and Kondo effect in quantum dots
We investigate the influence of an electromagnetic environment, characterized
by a finite impedance , on the Kondo effect in quantum dots. The
circuit voltage fluctuations couple to charge fluctuations in the dot and
influence the spin exchange processes transferring charge between the
electrodes. We discuss how the low-energy properties of a Kondo quantum dot
subject to dynamical Coulomb blockade resemble those of Kondo impurities in
Luttinger liquids. Using previous knowledge based on the bosonization of
quantum impurity models, we show that low-voltage conductance anomalies appear
at zero temperature. The conductance can vanish at low temperatures even in
presence of a screened impurity spin. Moreover, the quantitative determination
of the corresponding Kondo temperature depends on the full frequency-dependent
impedance of the circuit. This is demonstrated by a weak-coupling calculation
in the Kondo interaction, taking into account the full distribution of
excited environmental modes.Comment: 10 pages, 4 figures, revised version, new titl
Constraints on Light Pseudoscalars Implied by Tests of the Gravitational Inverse-Square Law
The exchange of light pseudoscalars between fermions leads to a
spin-independent potential in order g^4, where g is the Yukawa
pseudoscalar-fermion coupling constant. This potential gives rise to detectable
violations of both the weak equivalence principle (WEP) and the gravitational
inverse-square law (ISL), even if g is quite small. We show that when
previously derived WEP constraints are combined with those arisingfrom ISL
tests, a direct experimental limit on the Yukawa coupling of light
pseudoscalars to neutrons can be inferred for the first time (g_n^2/4pi < 1.6
\times 10^-7), along with a new (and significantly improved) limit on the
coupling of light pseudoscalars to protons.Comment: 12 pages, Revtex, with 1 Postscript figure (submitted to Physical
Review Letters
Long range neutrino forces in the cosmic relic neutrino background
Neutrinos mediate long range forces among macroscopic bodies in vacuum. When
the bodies are placed in the neutrino cosmic background, these forces are
modified. Indeed, at distances long compared to the scale , the relic
neutrinos completely screen off the 2-neutrino exchange force, whereas for
small distances the interaction remains unaffected.Comment: 8 pages, 2 figure
Towards azimuthal anisotropy of direct photons
Intensive radiation of magnetic bremsstrahlung type (synchrotron radiation)
resulting from the interaction of escaping quarks with the collective confining
colour field is discussed as a new possible mechanism of observed direct photon
anisotropy.Comment: 3 pages, Comments and references added, accepted to JETP Letters
(Pis'ma v ZhETF
Dirac-Foldy term and the electromagnetic polarizability of the neutron
We reconsider the Dirac-Foldy contribution to the neutron electric
polarizability. Using a Dirac equation approach to neutron-nucleus scattering,
we review the definitions of Compton continuum (), classical
static (), and Schr\"{o}dinger () polarizabilities
and discuss in some detail their relationship. The latter is the
value of the neutron electric polarizability as obtained from an analysis using
the Schr\"{o}dinger equation. We find in particular , where is the magnitude of the magnetic moment
of a neutron of mass . However, we argue that the static polarizability
is correctly defined in the rest frame of the particle, leading to
the conclusion that twice the Dirac-Foldy contribution should be added to
to obtain the static polarizability .Comment: 11 pages, RevTeX, to appear in Physical Review
Space-Time Evolution of Ultrarelativistic Quantum Dipoles in Quantum Electrodynamics
We discuss space-time evolution of ultrarelativistic quantum dipole in QED.
We show that the space-time evolution can be described, in a certain
approximation, by means of a regularized wave function, whose parameters are
determined by the process of the dipole creation by a local current. We derive
using these wave functions the dipole expansion law, that is found to coincide
parametrically in the leading order with the one suggested by Farrar,
Frankfurt,Liu and Strikman.Comment: 15 page
Initial correlations effects on decoherence at zero temperature
We consider a free charged particle interacting with an electromagnetic bath
at zero temperature. The dipole approximation is used to treat the bath
wavelengths larger than the width of the particle wave packet. The effect of
these wavelengths is described then by a linear Hamiltonian whose form is
analogous to phenomenological Hamiltonians previously adopted to describe the
free particle-bath interaction. We study how the time dependence of decoherence
evolution is related with initial particle-bath correlations. We show that
decoherence is related to the time dependent dressing of the particle. Moreover
because decoherence induced by the T=0 bath is very rapid, we make some
considerations on the conditions under which interference may be experimentally
observed.Comment: 16 pages, 1 figur
Variational study of the Holstein polaron
The paper deals with the ground and the first excited state of the polaron in
the one dimensional Holstein model. Various variational methods are used to
investigate both the weak coupling and strong coupling case, as well as the
crossover regime between them. Two of the methods, which are presented here for
the first time, introduce interesting elements to the understanding of the
nature of the polaron. Reliable numerical evidence is found that, in the strong
coupling regime, the ground and the first excited state of the self-trapped
polaron are well described within the adiabatic limit. The lattice vibration
modes associated with the self-trapped polarons are analyzed in detail, and the
frequency softening of the vibration mode at the central site of the small
polaron is estimated. It is shown that the first excited state of the system in
the strong coupling regime corresponds to the excitation of the soft phonon
mode within the polaron. In the crossover regime, the ground and the first
excited state of the system can be approximated by the anticrossing of the
self-trapped and the delocalized polaron state. In this way, the connection
between the behavior of the ground and the first excited state is qualitatively
explained.Comment: 11 pages, 4 figures, PRB 65, 14430
Casimir energy of a dilute dielectric ball with uniform velocity of light at finite temperature
The Casimir energy, free energy and Casimir force are evaluated, at arbitrary
finite temperature, for a dilute dielectric ball with uniform velocity of light
inside the ball and in the surrounding medium. In particular, we investigate
the classical limit at high temperature. The Casimir force found is repulsive,
as in previous calculations.Comment: 15 pages, 1 figur
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