22,333 research outputs found
Asymptotic Analysis of the Boltzmann Equation for Dark Matter Relics in the presence of a Running Dilaton and Space-Time Defects
The interplay of dilatonic effects in dilaton cosmology and stochastic
quantum space-time defects within the framework of string/brane cosmologies is
examined. The Boltzmann equation describes the physics of thermal
dark-matter-relic abundances in the presence of rolling dilatons. These
dilatons affect the coupling of stringy matter to D-particle defects, which are
generic in string theory. This coupling leads to an additional source term in
the Boltzmann equation. The techniques of asymptotic matching and
boundary-layer theory, which were recently applied by two of the authors (CMB
and SS) to a Boltzmann equation, are used here to find the detailed asymptotic
relic abundances for all ranges of the expectation value of the dilaton field.
The phenomenological implications for the search of supersymmetric dark matter
in current colliders, such as the LHC, are discussed
Baryonic Resonances from the Interactions of the Baryon Decuplet and Meson Octet
We study -wave interactions of the baryon decuplet with the octet of
pseudoscalar mesons using the lowest order chiral Lagrangian. We find two bound
states in the SU(3) limit corresponding to the octet and decuplet
representations. These are found to split into eight different trajectories in
the complex plane when the SU(3) symmetry is broken gradually. Finally, we are
able to provide a reasonable description for a good number of 4-star
resonances listed by the Particle Data Group. In particular, the
, the and the states are well
reproduced. We predict a few other resonances and also evaluate the couplings
of the observed resonances to the various channels from the residues at the
poles of the scattering matrix from where partial decay widths into different
channels can be evaluated.Comment: Contribution to the HADRON05 Conference, Rio de Janeiro, September
200
Evidence for an inflationary phase transition from the LSS and CMB anisotropy data
In the light of the recent Boomerang and Maxima observations of the CMB which
show an anomalously low second acoustic peak, we reexamine the prediction by
Adams et al (1997) that this would be the consequence of a 'step' in the
primordial spectrum induced by a spontaneous symmetry breaking phase transition
during primordial inflation. We demonstrate that a deviation from
scale-invariance around ~Mpc can simultaneously explain both
the feature identified earlier in the APM galaxy power spectrum as well the
recent CMB anisotropy data, with a baryon density consistent with the BBN
value. Such a break also allows a good fit to the data on cluster abundances
even for a critical density matter-dominated universe with zero cosmological
constant.Comment: 4 pages with 3 figures, LaTeX file using espcrc2.sty to appear on the
Proceedings of "Euroconference on Frontiers in Particle Astrophysics and
Cosmology",Sant Feliu de Guixols,Spain,30th September-5th October of 200
Electrical transport properties of nanostructured ferromagnetic perovskite oxides La_0.67Ca_0.33MnO_3 and La_0.5Sr_0.5CoO_3 at low temperatures (5 K > T >0.3 K) and high magnetic field
We report a comprehensive study of the electrical and magneto-transport
properties of nanocrystals of La_0.67Ca_0.33MnO_3 (LCMO) (with size down to 15
nm) and La_0.5Sr_0.5CoO_3 (LSCO) (with size down to 35 nm) in the temperature
range 0.3 K to 5 K and magnetic fields upto 14 T. The transport,
magnetotransport and non-linear conduction (I-V curves) were analysed using the
concept of Spin Polarized Tunnelling in the presence of Coulomb blockade. The
activation energy of transport, \Delta, was used to estimate the tunnelling
distances and the inverse decay length of the tunnelling wave function (\chi)
and the height of the tunnelling barrier (\Phi_B). The magnetotransport data
were used to find out the magnetic field dependences of these tunnelling
parameters. The data taken over a large magnetic field range allowed us to
separate out the MR contributions at low temperatures arising from tunnelling
into two distinct contributions. In LCMO, at low magnetic field, the transport
and the MR are dominated by the spin polarization, while at higher magnetic
field the MR arises from the lowering of the tunnel barrier by the magnetic
field leading to an MR that does not saturate even at 14 T. In contrast, in
LSCO, which does not have substantial spin polarization, the first contribution
at low field is absent, while the second contribution related to the barrier
height persists. The idea of inter-grain tunnelling has been validated by
direct measurements of the non-linear I-V data in this temperature range and
the I-V data was found to be strongly dependent on magnetic field. We made the
important observation that a gap like feature (with magnitude ~ E_C, the
Coulomb charging energy) shows up in the conductance g(V) at low bias for the
systems with smallest nanocrystal size at lowest temperatures (T < 0.7 K). The
gap closes as the magnetic field and the temperature are increased.Comment: 13 figure
Infinitely many inequivalent field theories from one Lagrangian
Logarithmic time-like Liouville quantum field theory has a generalized PT
invariance, where T is the time-reversal operator and P stands for an S-duality
reflection of the Liouville field . In Euclidean space the Lagrangian of
such a theory, , is analyzed
using the techniques of PT-symmetric quantum theory. It is shown that L defines
an infinite number of unitarily inequivalent sectors of the theory labeled by
the integer n. In one-dimensional space (quantum mechanics) the energy spectrum
is calculated in the semiclassical limit and the mth energy level in the nth
sector is given by .Comment: 5 pages, 7 figure
A Genomic Point Mutation in the Extracellular Domain of the Thyrotropin Receptor in Patients with Graves’ Ophthalmopathy
Orbital and pretibial fibroblasts are targets of autoimmune attack in Graves' ophthalmopathy (GO) and pretibial dermopathy (PTD). The fibroblast autoantigen involved in these peripheral manifestations of Graves' disease and the reason for the association of GO and PTD with hyperthyroidism are unknown. RNA encoding the full-length extracellular domain of the TSH receptor has been demonstrated in orbital and dermal fibroblasts from patients with GO and normal subjects, suggesting a possible antigenic link between fibroblasts and thyrocytes. RNA was isolated from cultured orbital, pretibial, and abdominal fibroblasts obtained from patients with severe GO (n = 22) and normal subjects (n = 5). RNA was reverse transcribed, and the resulting cDNA was amplified by the polymerase chain reaction, using primers spanning overlapping regions of the entire extracellular domain of the TSH receptor. Nucleotide sequence analysis showed an A for C substitution in the first position of codon 52 in 2 of the patients, both of whom had GO, PTD, and acropachy. Genomic DNA isolated from the 2 affected patients, and not from an additional 12 normal subjects, revealed the codon 52 mutation by direct sequencing and AciI restriction enzyme digestions. In conclusion, we have demonstrated the presence of a genomic point mutation, leading to a threonine for proline amino acid shift in the predicted peptide, in the extracellular domain of the TSH receptor in two patients with severe GO, PTD, acropachy, and high thyroid-stimulating immunoglobulin levels. RNA encoding this mutant product was demonstrated in the fibroblasts of these patients. We suggest that the TSH receptor may be an important fibroblast autoantigen in GO and PTD, and that this mutant form of the receptor may have unique immunogenic properties
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