844 research outputs found
Crossover from Luttinger- to Fermi-liquid behavior in strongly anisotropic systems in large dimensions
We consider the low-energy region of an array of Luttinger liquids coupled by
a weak interchain hopping. The leading logarithmic divergences can be re-summed
to all orders within a self-consistent perturbative expansion in the hopping,
in the large-dimension limit. The anomalous exponent scales to zero below the
one-particle crossover temperature. As a consequence, coherent quasiparticles
with finite weight appear along the whole Fermi surface. Extending the
expansion self-consistently to all orders turns out to be crucial in order to
restore the correct Fermi-liquid behavior.Comment: Shortened version to appear in Physical Review Letter
Congenital disorder of glycosylation type Id (CDG Id): phenotypic, biochemical and molecular characterization of a new patient
Summary: Congenital disorders of glycosylation (CDG) are a family of multisystem inherited disorders caused by defects in the biosynthesis of N- or O-glycans. Among the many different subtypes of CDG, the defect of a mannosyltransferase encoded by the human ALG3 gene (chromosome 3q27) is known to cause CDG Id. Six patients with CDG Id have been described in the literature so far. We further delineate the clinical, biochemical, neuroradiological and molecular features of CDG Id by reporting an additional patient bearing a novel missense mutation in the ALG3 gene. All patients with CDG Id display a slowly progressive encephalopathy with microcephaly, severe psychomotor retardation and epileptic seizures. They also share some typical dysmorphic features but they do not present the multisystem involvement observed in other CDG syndromes or any biological marker abnormalities. Unusually marked osteopenia is a feature in some patients and may remain undiagnosed until revealed by pathological fractures. Serum transferrin screening for CDG should be extended to all patients with encephalopathy of unknown origin, even in the absence of multisystem involvemen
On the Possibility of Observing the Shapiro Effect for Pulsars in Globular Clusters
For pulsars in globular clusters, we suggest using observations of the
relativistic time delay of their radiation in the gravitational eld of a
massive body (the Shapiro effect) located close to the line of sight to detect
and identify invisible compact objects and to study the distribution of both
visible and dark matter in globular clusters and various components of the
Galaxy. We have derived the dependences of the event probability on the
Galactic latitude and longitude of sources for two models of the mass
distribution in the Galaxy: the classical Bahcall-Soneira model and the more
recent Dehnen-Binney model. Using three globular clusters (M15, 47 Tuc, Terzan
5) as an example, we show that the ratios of the probability of the events due
to the passages of massive Galactic objects close to the line of sight to the
parameter f2 for pulsars in the globular clusters 47 Tuc and M15 are comparable
to those for close passages of massive objects in the clusters themselves and
are considerably higher than those for the cluster Terzan 5. We have estimated
the rates of such events. We have determined the number of objects near the
line of sight toward the pulsar that can produce a modulation of its pulse
arrival times characteristic of the effect under consideration; the population
of brown dwarfs in the Galactic disk, whose concentration is comparable to that
of the disk stars, has been taken into account for the first time.Comment: 26 pages, 9 figure
Neutrino opacity in magnetised hot and dense nuclear matter
We study the neutrino interaction rates in hot matter at high densities in
the presence of uniform magnetic field. The neutrino cross-sections involving
both the charged current absorption and neutral current scattering reactions on
baryons and leptons have been considered. We have in particular considered the
interesting case when the magnetic field is strong enough to completely
polarise the protons and electrons in supernovae and neutron stars. The opacity
in such a situation is considerably modified and the cross-section develops
anisotropy. This has implications for phenomenon invoked in the literature to
explain the observed pulsar kicks.Comment: 22 latex pages and 7 postscript figure
Instability of the marginal commutative model of tunneling centers interacting with metallic environment: Role of the electron-hole symmetry breaking
The role of the electron-hole symmetry breaking is investigated for a
symmetrical commutative two-level system in a metal using the multiplicative
renormalization group in a straightforward way. The role of the symmetries of
the model and the path integral technique are also discussed in detail. It is
shown that the electron-hole symmetry breaking may make the model
non-commutative and generate the assisted tunneling process which is, however,
too small itself to drive the system into the vicinity of the two-channel Kondo
fixed point. While these results are in qualitative agreement with those of
Moustakas and Fisher (Phys. Rev. B 51, 6908 (1995), ibid 53, 4300 (1996)) the
scaling equations turn out to be essentially different. We show that the main
reason for this difference is that the procedure for the elimination of the
high energy degrees of freedom used by Moustakas and Fisher leaves only the
free energy invariant, however, the couplings generated are not connected to
the dynamical properties in a straightforward way and should be interpreted
with care. These latter results might have important consequences in other
cases where the path integral technique is used to produce the scaling
equations and calculate physical quantities.Comment: latex, figures in ps file adde
Leptonic CP Violation in Supersymmetric Standard Model
We point out the possibility of spontaneous and hard CP-violation in the
scalar potential of R-parity broken supersymmetric Standard Model. The
existence of spontaneous CP-violation depends crucially on the R-parity
breaking terms in the superpotential and, in addition, on the choice of the
soft supersymmetry breaking terms. Unlike in theories with R-parity
conservation, it is natural, in the context of the present model, for the
sneutrinos to acquire (complex) vacuum expectation values. In the context of
this model we examine here the global implications, like the strength of the
CP-violating interactions and the neutrino masses.Comment: REVTEX, 15 page
Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition
In this paper we investigate the effect of stochasticity in the spatial and
temporal distribution of supernova remnants on the spectrum and chemical
composition of cosmic rays observed at Earth. The calculations are carried out
for different choices of the diffusion coefficient D(E) experienced by cosmic
rays during propagation in the Galaxy. In particular, at high energies we
assume that D(E)\sim E^{\delta}, with and being the
reference scenarios. The large scale distribution of supernova remnants in the
Galaxy is modeled following the distribution of pulsars, with and without
accounting for the spiral structure of the Galaxy. We find that the stochastic
fluctuations induced by the spatial and temporal distribution of supernovae,
together with the effect of spallation of nuclei, lead to mild but sensible
violations of the simple, leaky-box-inspired rule that the spectrum observed at
Earth is with , where
is the slope of the cosmic ray injection spectrum at the sources. Spallation of
nuclei, even with the small rates appropriate for He, may account for slight
differences in spectral slopes between different nuclei, providing a possible
explanation for the recent CREAM observations. For we find that
the slope of the proton and helium spectra are and
respectively at energies above 1 TeV (to be compared with the measured values
of and ). For the hardening of the He
spectra is not observed. We also comment on the effect of time dependence of
the escape of cosmic rays from supernova remnants, and of a possible clustering
of the sources in superbubbles. In a second paper we will discuss the
implications of these different scenarios for the anisotropy of cosmic rays.Comment: 28 pages, To appear in JCA
Relativistic theory of inverse beta-decay of polarized neutron in strong magnetic field
The relativistic theory of the inverse beta-decay of polarized neutron, , in strong magnetic field is developed. For the proton
wave function we use the exact solution of the Dirac equation in the magnetic
filed that enables us to account exactly for effects of the proton momentum
quantization in the magnetic field and also for the proton recoil motion. The
effect of nucleons anomalous magnetic moments in strong magnetic fields is also
discussed. We examine the cross section for different energies and directions
of propagation of the initial neutrino accounting for neutrons polarization. It
is shown that in the super-strong magnetic field the totally polarized neutron
matter is transparent for neutrinos propagating antiparallel to the direction
of polarization. The developed relativistic approach can be used for
calculations of cross sections of the other URCA processes in strong magnetic
fields.Comment: 41 pages in LaTex including 11 figures in PostScript, discussion on
nucleons AMM interaction with magnetic field is adde
Resonance in One--Dimensional Fermi--Edge Singularity
The problem of the Fermi--edge singularity in a one--dimensional
Tomonaga--Luttinger liquid is reconsidered. The backward scattering of the
conduction band electrons on the impurity--like hole in the valence band is
analyzed by mapping the problem onto a Coulomb gas theory. For the case when
the electron--electron interaction is repulsive the obtained exponent of the
one--dimensional Fermi--edge singularity appears to be different from the
exponent found in the previous studies. It is shown that the infrared physics
of the Fermi--edge singularity in the presence of backward scattering and
electron--electron repulsion resembles the physics of the Kondo problem.Comment: 38 pages and 1 figure, to be published in PR
Cosmological constraints on R-parity violation from neutrino decay
If the neutrino mass is non-zero, as hinted by several experiments, then
R-parity-violating supersymmetric Yukawa couplings can drive a heavy neutrino
decay into lighter states. The heavy neutrino may either decay radiatively into
a lighter neutrino, or it may decay into three light neutrinos through a
Z-mediated penguin. For a given mass of the decaying neutrino, we calculate its
lifetime for the various modes, each mode requiring certain pairs of
R-parity-violating couplings be non-zero. We then check whether the calculated
lifetimes fall in zones allowed or excluded by cosmological requirements. For
the latter case, we derive stringent new constraints on the corresponding
products of R-parity-violating couplings for given values of the decaying
neutrino mass.Comment: 13 pages, Latex, uses axodraw.sty; version to appear in Physical
Review
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