2,516 research outputs found
Decoherent Neutrino Mixing, Dark Energy and Matter-Antimatter Asymmetry
A CPT violating decoherence scenario can easily account for all the
experimental evidence in the neutrino sector including LSND. In this work it is
argued that this framework can also accommodate the Dark Energy content of the
Universe, as well as the observed matter-antimatter asymmetry.Comment: 6 pages, no figures, some typos corrected, and discussion modified
below eq (3), no effects on conclusion
Atomic Electric Dipole Moments: The Schiff Theorem and Its Corrections
Searches for the permanent electric dipole moments (EDMs) of diamagnetic
atoms provide powerful probes of CP-violating hadronic and semileptonic
interactions. The theoretical interpretation of such experiments, however,
requires careful implementation of a well-known theorem by Schiff that implies
a vanishing net EDM for an atom built entirely from point-like, nonrelativistic
constituents that interact only electrostatically. Any experimental observation
of a nonzero atomic EDM would result from corrections to the point-like,
nonrelativistic, electrostatic assumption. We reformulate Schiff's theorem at
the operator level and delineate the electronic and nuclear operators whose
atomic matrix elements generate corrections to "Schiff screening". We obtain a
form for the operator responsible for the leading correction associated with
finite nuclear size -- the so-called "Schiff moment" operator -- and observe
that it differs from the corresponding operator used in previous Schiff moment
computations. We show that the more general Schiff moment operator reduces to
the previously employed operator only under certain approximations that are not
generally justified. We also identify other corrections to Schiff screening
that may not be included properly in previous theoretical treatments. We
discuss practical considerations for obtaining a complete computation of
corrections to Schiff screening in atomic EDM calculations.Comment: 31 pages, 2 figures, typeset by REVTe
Statistical Origin of Black Hole Entropy in Matrix Theory
The statistical entropy of black holes in M-theory is considered. Assuming
Matrix theory is the discretized light-cone quantization of a theory with
eleven-dimensional Lorentz invariance, we map the counting problem onto the
original Gibbons-Hawking calculation of the thermodynamic entropy.Comment: 9 pages, harvmac, (v2 References added, typo fixed), (v3 Some
clarifying comments added.
Entanglement Entropy in Critical Phenomena and Analogue Models of Quantum Gravity
A general geometrical structure of the entanglement entropy for spatial
partition of a relativistic QFT system is established by using methods of the
effective gravity action and the spectral geometry. A special attention is
payed to the subleading terms in the entropy in different dimensions and to
behaviour in different states. It is conjectured, on the base of relation
between the entropy and the action, that in a fundamental theory the ground
state entanglement entropy per unit area equals , where is the
Newton constant in the low-energy gravity sector of the theory. The conjecture
opens a new avenue in analogue gravity models. For instance, in higher
dimensional condensed matter systems, which near a critical point are described
by relativistic QFT's, the entanglement entropy density defines an effective
gravitational coupling. By studying the properties of this constant one can get
new insights in quantum gravity phenomena, such as the universality of the
low-energy physics, the renormalization group behavior of , the
statistical meaning of the Bekenstein-Hawking entropy.Comment: 13 pages, published version, minor changes in the abstract, new
reference
The neutron electric dipole form factor in the perturbative chiral quark model
We calculate the electric dipole form factor of the neutron in a perturbative
chiral quark model, parameterizing CP-violation of generic origin by means of
effective electric dipole moments of the constituent quarks and their
CP-violating couplings to the chiral fields. We discuss the relation of these
effective parameters to more fundamental ones such as the intrinsic electric
and chromoelectric dipole moments of quarks and the Weinberg parameter. From
the existing experimental upper limits on the neutron EDM we derive constraints
on these CP-violating parameters.Comment: 20 pages, 3 figure
Spherically symmetric space-time with the regular de Sitter center
The requirements are formulated which lead to the existence of the class of
globally regular solutions to the minimally coupled GR equations which are
asymptotically de Sitter at the center. The brief review of the resulting
geometry is presented. The source term, invariant under radial boots, is
classified as spherically symmetric vacuum with variable density and pressure,
associated with an r-dependent cosmological term, whose asymptotic in the
origin, dictated by the weak energy condition, is the Einstein cosmological
term. For this class of metrics the ADM mass is related to both de Sitter
vacuum trapped in the origin and to breaking of space-time symmetry. In the
case of the flat asymptotic, space-time symmetry changes smoothly from the de
Sitter group at the center to the Lorentz group at infinity. Dependently on
mass, de Sitter-Schwarzschild geometry describes a vacuum nonsingular black
hole, or G-lump - a vacuum selfgravitating particlelike structure without
horizons. In the case of de Sitter asymptotic at infinity, geometry is
asymptotically de Sitter at both origin and infinity and describes, dependently
on parameters and choice of coordinates, a vacuum nonsingular cosmological
black hole, selfgravitating particlelike structure at the de Sitter background
and regular cosmological models with smoothly evolving vacuum energy density.Comment: Latex, 10 figures, extended version of the plenary talk at V
Friedmann Intern. Conf. on Gravitation and Cosmology, Brazil 2002, to appear
in Int.J.Mod.Phys.
Inhaled Polymyxin in Treatment of Elderly Patients with Severe Community-Acquired Klebsiella pneumoniae-Induced Pneumonia
Background. Inhaled administration of antibacterial drugs (ABD) is a new insufficiently studied area of modern pulmonology. Its feasible advantages comprise a targeted drug delivery to the infection site, amplified antibiotic concentration in tracheobronchial secretion and reduced systemic toxicity risks. The most common inhaled ABDs include aminoglycosides and polymyxinE (colistin).Aim. A comparison of patient cohorts with severe communityacquired pneumonia induced by Klebsiella pneumoniae receiving and not receiving inhaled colistin.Materials and methods. The study conducted is a retrospective multicentre controlled nonrandomised assay. Among the 45 patients included, 20 were and 25 were not receiving colistin inhalation. The endpoint was survival. Data were analysed with Statistica 6.0.Results and discussion. The cohorts differed significantly neither in the main clinical and laboratory values, nor in point scoring of severity and outcome. However, statistical significance was obtained for differences in the ALV (p = 0.04) and pneumonia resolution (p = 0.044) times.Conclusion. Inhaled polymyxinsupplemented therapy for severe communityacquired pneumonia induced by Kl. pneumoniae significantly reduces the ALV and pneumonia resolution times in elderly and senile patients but does not affect survival
Space-Time Foam may Violate the Principle of Equivalence
The interactions of different particle species with the foamy space-time
fluctuations expected in quantum gravity theories may not be universal, in
which case different types of energetic particles may violate Lorentz
invariance by varying amounts, violating the equivalence principle. We
illustrate this possibility in two different models of space-time foam based on
D-particle fluctuations in either flat Minkowski space or a stack of
intersecting D-branes. Both models suggest that Lorentz invariance could be
violated for energetic particles that do not carry conserved charges, such as
photons, whereas charged particles such electrons would propagate in a
Lorentz-inavariant way. The D-brane model further suggests that gluon
propagation might violate Lorentz invariance, but not neutrinos. We argue that
these conclusions hold at both the tree (lowest-genus) and loop (higher-genus)
levels, and discuss their implications for the phenomenology of quantum
gravity.Comment: 20 pages, 4 figures, the version accepted for publication in the
International Journal of Modern Physics
Measurement of the electron's electric dipole moment using YbF molecules: methods and data analysis
We recently reported a new measurement of the electron's electric dipole
moment using YbF molecules [Nature 473, 493 (2011)]. Here, we give a more
detailed description of the methods used to make this measurement, along with a
fuller analysis of the data. We show how our methods isolate the electric
dipole moment from imperfections in the experiment that might mimic it. We
describe the systematic errors that we discovered, and the small corrections
that we made to account for these. By making a set of additional measurements
with greatly exaggerated experimental imperfections, we find upper bounds on
possible uncorrected systematic errors which we use to determine the systematic
uncertainty in the measurement. We also calculate the size of some systematic
effects that have been important in previous electric dipole moment
measurements, such as the motional magnetic field effect and the geometric
phase, and show them to be negligibly small in the present experiment. Our
result is consistent with an electric dipole moment of zero, so we provide
upper bounds to its size at various confidence levels. Finally, we review the
prospects for future improvements in the precision of the experiment.Comment: 35 pages, 15 figure
Dynamical Determination of the Metric Signature in Spacetime of Nontrivial Topology
The formalism of Greensite for treating the spacetime signature as a
dynamical degree of freedom induced by quantum fields is considered for
spacetimes with nontrivial topology of the kind , for varying . It is shown that a dynamical origin for the Lorentzian
signature is possible in the five-dimensional space with small torus radius (periodic boundary conditions), as well as in
four-dimensional space with trivial topology. Hence, the possibility exists
that the early universe might have been of the Kaluza-Klein type, \ie
multidimensional and of Lorentzian signature.Comment: 10 pages, LaTeX file, 4 figure
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