2,131 research outputs found
Stringent constraint on the scalar-neutrino coupling constant from quintessential cosmology
An extremely light (), slowly-varying scalar
field (quintessence) with a potential energy density as large as 60% of
the critical density has been proposed as the origin of the accelerated
expansion of the Universe at present. The interaction of this smoothly
distributed component with another predominately smooth component, the cosmic
neutrino background, is studied. The slow-roll approximation for generic potentials may then be used to obtain a limit on the scalar-neutrino coupling
constant, found to be many orders of magnitude more stringent than the limits
set by observations of neutrinos from SN 1987A. In addition, if quintessential
theory allows for a violation of the equivalence principle in the sector of
neutrinos, the current solar neutrino data can probe such a violation at the
10^{-10} level.Comment: 7 pages, MPLA in press, some parts disregarded and a footnote adde
A bound on the scale of spacetime noncommutativity from the reheating phase after inflation
In an approach to noncommutative gauge theories, where the full
noncommutative behavior is delimited by the presence of the UV and IR cutoffs,
we consider the possibility of describing a system at a temperature T in a box
of size L. Employing a specific form of UV/IR relationship inherent in such an
approach of restrictive noncommutativity, we derive, for a given temperature T,
an upper bound on the parameter of spacetime noncommutativity Lambda_NC ~
|theta|^{-1/2}. Considering such epochs in the very early universe which are
expected to reflect spacetime noncommutativity to a quite degree, like the
reheating stage after inflation, or believable pre-inflation
radiation-dominated epochs, the best limits on Lambda_NC are obtained. We also
demonstrate how the nature and size of the thermal system (for instance, the
Hubble distance versus the future event horizon) can affect our bounds.Comment: 9 pages, a reference added, to appear in PL
On finite--temperature and --density radiative corrections to the neutrino effective potential in the early Universe
Finite-temperature and -density radiative corrections to the neutrino
effective potential in the otherwise CP-symmetric early Universe are considered
in the real-time approach of Thermal Field Theory. A consistent perturbation
theory endowed with the hard thermal loop resummation techniques developed by
Braaten and Pisarski is applied. Special attention is focused on the question
whether such corrections can generate any nonzero contribution to the
CP-symmetric part of the neutrino potential, if the contact approximation for
the W-propagator is used.Comment: 11 pages, revtex styl
Upgrade of the ATLAS Muon Trigger for the SLHC
The outer shell of the ATLAS experiment at the LHC consists of a system of
toroidal air-core magnets in order to allow for the precise measurement of the
transverse momentum p of muons, which in many physics channels are a
signature of interesting physics processes. For the precise determination of
the muon momentum Monitored Drift Tube chambers (MDT) with high position
accuracy are used, while for the fast identification of muon tracks chambers
with high time resolution are used, able to select muons above a predefined
p threshold for use in the first Level of the ATLAS triggering system
(Level-1 trigger). When the luminosity of the LHC will be upgraded to 4-5 times
the present nominal value (SLHC) in about a decade from now, an improvement of
the selectivity of the ATLAS Level-1 triggering system will be mandatory in
order to cope with the maximum allowed trigger rate of 100 kHz. For the Level-1
trigger of the ATLAS muon spectrometer this means an increase of the p
threshold for single muons. Due to the limited spatial resolution of the
trigger chambers, however, the selectivity for tracks above ~20 GeV/c is
insufficient for an effective reduction of the Level-1 rate. We describe how
the track coordinates measured in the MDT precision chambers can be used to
decisively improve the selectivity for high momentum tracks. The resulting
increase in latency will also be discussed.Comment: These are the proceedings of a presentation given at the Topical
Workshop of Electronics for Particle Physics 2010 in Aachen, Germany (sept.,
20-24, 2010
Dynamical approach to chains of scatterers
Linear chains of quantum scatterers are studied in the process of
lengthening, which is treated and analysed as a discrete dynamical system
defined over the manifold of scattering matrices. Elementary properties of such
dynamics relate the transport through the chain to the spectral properties of
individual scatterers. For a single-scattering channel case some new light is
shed on known transport properties of disordered and noisy chains, whereas
translationally invariant case can be studied analytically in terms of a simple
deterministic dynamical map. The many-channel case was studied numerically by
examining the statistical properties of scatterers that correspond to a certain
type of transport of the chain i.e. ballistic or (partially) localised.Comment: 16 pages, 7 figure
Performance of the ATLAS Muon Drift-Tube Chambers at High Background Rates and in Magnetic Fields
The ATLAS muon spectrometer uses drift-tube chambers for precision tracking.
The performance of these chambers in the presence of magnetic field and high
radiation fluxes is studied in this article using test-beam data recorded in
the Gamma Irradiation Facility at CERN. The measurements are compared to
detailed predictions provided by the Garfield drift-chamber simulation
programme
Combining Density-Functional Theory with Low-Temperature, Polarized Terahertz Spectroscopy of Single Crystals Explicates the Fundamental Modes of L-Alanine
While the fundamental modes of amino acids are accessible in principle by
terahertz spectroscopy, reports to date have several shortcomings: (a) material
of uncertain purity and morphology and diluted in a binder material is
employed; (b) consequently, vibrations along all crystal axes are excited
simultaneously; (c) data is restricted to room temperature, where resonances
are broad and the background dominant; (d) comparison with theory has been
unsatisfactory (in part because the theory assumes zero temperature). Here, we
overcome all four obstacles, in reporting detailed polarized THz spectra of
single-crystal L-alanine, assigning vibrational modes using density functional
theory, and comparing the calculated dipole moment vector direction to the
electric field polarization of the measured spectra. The direct and detailed
comparison of theory with experiment has corrected previous mode assignments
for L-alanine, as well as revealed unreported modes, previously obscured by
closely-spaced spectral absorptions. The fundamental modes are thereby
determined.Comment: 4 Pages for the main manuscript, and 1 page for references. 3 figure
Holography and Variable Cosmological Constant
An effective local quantum field theory with UV and IR cutoffs correlated in
accordance with holographic entropy bounds is capable of rendering the
cosmological constant (CC) stable against quantum corrections. By setting an IR
cutoff to length scales relevant to cosmology, one easily obtains the currently
observed rho_Lambda ~ 10^{-47} GeV^4, thus alleviating the CC problem. It is
argued that scaling behavior of the CC in these scenarios implies an
interaction of the CC with matter sector or a time-dependent gravitational
constant, to accommodate the observational data.Comment: 7 pages, final version accepted by PR
Embedding the Texture of the Neutrino Mass Matrix into the MaVaNs Scenario
We have embedded the texture of the neutrino mass matrix with three families
into the MaVaNs scenario. We take the power-law potential of the acceleron
field and a typical texture of active neutrinos, which is derived by the D_4
symmetry and predicts the maximal mixing of the atmospheric neutrino and the
vanishing U_{e3}. The effect of couplings among the dark fermion and active
neutrinos are studied by putting the current cosmological data and the
terrestrial neutrino experimental data. It is found that the neutrino flavor
mixings evolve as well as the neutrino masses. Especially, U_{e3} develops into
the non-vanishing one and \theta_{atm} deviates from the maximal mixing due to
couplings among the dark fermion and active neutrinos.Comment: Sections 3 and 4 are changed and one table is added. 16pages and 2
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