2,944 research outputs found
Brane-Production and the Neutrino-Nucleon cross section at Ultra High Energies in Low Scale Gravity Models
The origin of the ultra high energy cosmic ray (UHECR) showers has remained
as a mystery among particle physicists and astrophysicists. In low scale
gravity models, where the neutrino-nucleon cross section rises to typical
hadronic values at energies above eV, the neutrino becomes a
candidate for the primary that initiates these showers. We calculate the
neutrino-nucleon cross section at ultra high energies by assuming that it is
dominated by the production of p-branes. We show, using a generalized
Randall-Sundrum model, that the neutrino-nucleon cross-section at neutrino
energies of GeV is of the order of 100 mb, which is required for
explaining UHECR events. Similar result also follows in other models such as
the Lykken-Randall model.Comment: 13 pages, 2 figures, significantly revised version, no change in
conclusion
NiS - An unusual self-doped, nearly compensated antiferromagnetic metal
NiS, exhibiting a text-book example of a first-order transition with many
unusual properties at low temperatures, has been variously described in terms
of conflicting descriptions of its ground state during the past several
decades. We calculate these physical properties within first-principle
approaches based on the density functional theory and conclusively establish
that all experimental data can be understood in terms of a rather unusual
ground state of NiS that is best described as a self-doped, nearly compensated,
antiferromagnetic metal, resolving the age-old controversy. We trace the origin
of this novel ground state to the specific details of the crystal structure,
band dispersions and a sizable Coulomb interaction strength that is still
sub-critical to drive the system in to an insulating state. We also show how
the specific antiferromagnetic structure is a consequence of the less-discussed
90 degree and less than 90 degree superexchange interactions built in to such
crystal structures
Rare Coinfection of Scrub Typhus and Malaria in Immunocompetent Person
Scrub Typhus, or tsutsugamushi disease is a febrile illness caused by bacteria of the family Rickettsiaceae and named Orientia tsutsugamushi. Recently it has been found to endemic in Subhimalayan region of India.Malaria is highly endemic in rest of India but its prevalence is low in Subhimalayan region because of the altitude. We report a rare case of a patient having coinfection with scrub typhus and malaria
Non-Abelian symmetries and disorder: a broad non-ergodic regime and anomalous thermalization
Symmetries play a central role in single-particle localization. Recent
research focused on many-body localized (MBL) systems, characterized by new
kind of integrability, and by the area-law entanglement of eigenstates. We
investigate the effect of a non-Abelian symmetry on the dynamical
properties of a disordered Heisenberg chain. While symmetry is
inconsistent with the conventional MBL, a new non-ergodic regime is possible.
In this regime, the eigenstates exhibit faster than area-law, but still a
strongly sub-thermal scaling of entanglement entropy. Using exact
diagonalization, we establish that this non-ergodic regime is indeed realized
in the strongly disordered Heisenberg chains. We use real-space renormalization
group (RSRG) to construct approximate excited eigenstates, and show their
accuracy for systems of size up to . As disorder strength is decreased, a
crossover to the thermalizing phase occurs. To establish the ultimate fate of
the non-ergodic regime in the thermodynamic limit, we develop a novel approach
for describing many-body processes that are usually neglected by RSRG,
accessing systems of size . We characterize the resonances that arise
due to such processes, finding that they involve an ever growing number of
spins as the system size is increased. The probability of finding resonances
grows with the system size. Even at strong disorder, we can identify a large
lengthscale beyond which resonances proliferate. Presumably, this eventually
would drive the system to a thermalizing phase. However, the extremely long
thermalization time scales indicate that a broad non-ergodic regime will be
observable experimentally. Our study demonstrates that symmetries control
dynamical properties of disordered, many-body systems. The approach introduced
here provides a versatile tool for describing a broad range of disordered
many-body systems.Comment: 25 pages, 21 figure
Reheating the D-brane universe via instant preheating
We investigate a possibility of reheating in a scenario of D-brane inflation
in a warped deformed conifold background which includes perturbative
corrections to throat geometry sourced by chiral operator of dimension 3/2 in
the CFT. The effective D-brane potential, in this case, belongs to the class of
non-oscillatory models of inflation for which the conventional reheating
mechanism does not work. We find that gravitational particle production is
inefficient and leads to reheating temperature of the order of . We
show that instant preheating is quite suitable to the present scenario and can
easily reheat universe to a temperature which is higher by about three orders
of magnitudes than its counter part associated with gravitational particle
production. The reheating temperature is shown to be insensitive to a
particular choice of inflationary parameters suitable to observations.Comment: 6 pages and 4 figures, replaced with revised version, to appear in
PR
Amidinate Ligands in Zinc coordination sphere: Synthesis and structural diversity
A one-pot reaction involving neosilyllithium and three different carbodiimides (RN=C=NR, R=cyclohexyl, isopropyl and tert-butyl) in diethyl ether, followed by the addition of anhydrous ZnCl2, afforded, in high yield, corresponding homoleptic zinc amidinate complexes having the molecular formulae [Zn{CyN =C(CH2SiMe3)NCy}2] (1), [Zn{ i PrN =C(CH2SiMe3)N i Pr}2] (2) and [Zn{ t BuN =C(CH2SiMe3) N t Bu}2] (3), respectively, and amidinato moieties in the zinc coordination sphere. Solid state structures of complexes 1-3 are reported thereafter - all the three complexes are isostructural, and each of them consists of two four-membered metallacycles
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