13,224 research outputs found
Re/Os constraint on the time-variability of the fine-structure constant
We argue that the accuracy by which the isochron parameters of the decay
are determined by dating iron meteorites may
not directly constrain the possible time-dependence of the decay rate and hence
of the fine-structure constant . From this point of view, some of the
attempts to analyze the Oklo constraint and the results of the QSO absorption
lines are re-examined.Comment: 7 pages, 3 figures; v2, revised top sentence on p.
Baryogenesis and Gravitino Dark Matter in Gauge-Mediated Supersymmetry-Breaking Models
We discuss two cosmological issues in a generic gauge-mediated supersymmetry
(SUSY)-breaking model, namely the Universe's baryon asymmetry and the gravitino
dark-matter density. We show that both problems can be simultaneously solved if
there exist extra matter multiplets of a SUSY-invariant mass of the order of
the ``-term'', as suggested in several realistic SUSY grand-unified
theories. We propose an attractive scenario in which the observed baryon
asymmetry is produced in a way totally independent of the reheating temperature
of inflation without causing any cosmological gravitino problem. Furthermore,
in a relatively wide parameter space, we can also explain the present mass
density of cold dark matter by the thermal relics of the gravitinos without an
adjustment of the reheating temperature of inflation. We point out that there
is an interesting relation between the baryon asymmetry and the dark-matter
density.Comment: 20 pages, 2 figure
Remarks on the Collective Quantization of the SU(2) Skyrme Model
We point out the question of ordering momentum operator in the canonical
\break quantization of the SU(2) Skyrme Model. Thus, we suggest a new
definition for the momentum operator that may solve the infrared problem that
appears when we try to minimize the Quantum Hamiltonian.Comment: 8 pages, plain tex, IF/UFRJ/9
Quantum-Mechanical Detection of Non-Newtonian Gravity
In this work the possibility of detecting the presence of a Yukawa term, as
an additional contribution to the usual Newtonian gravitational potential, is
introduced. The central idea is to analyze the effects at quantum level
employing interference patterns (at this respect the present proposal resembles
the Colella, Overhauser and Werner experiment), and deduce from it the possible
effects that this Yukawa term could have. We will prove that the corresponding
interference pattern depends on the phenomenological parameters that define
this kind of terms. Afterwards, using the so called restricted path integral
formalism, the case of a particle whose position is being continuously
monitored, is analyzed, and the effects that this Yukawa potential could have
on the measurement outputs are obtained. This allows us to obtain another
scheme that could lead to the detection of these terms. This last part also
renders new theoretical predictions that could enable us to confront the
restricted path integral formalism against some future experiments.Comment: 17 pages, accepted in International Journal of Modern Physics
Upper Bound On Gluino Mass From Thermal Leptogenesis
Thermal leptogenesis requires the reheating temperature T_R \gsim 3\times
10^{9} GeV, which contradicts a recently obtained constraint on the reheating
temperature, T_R \lsim 10^6 GeV, for the gravitino mass of 100 GeV-10 TeV.
This stringent constraint comes from the fact that the hadronic decays of
gravitinos destroy very efficiently light elements produced by the Big-Bang
nucleosynthesis. However, it is not applicable if the gravitino is the lightest
supersymmetric particle (LSP). We show that this solution to the gravitino
problem works for the case where the next LSP is a scalar charged lepton or a
scalar neutrino. We point out that there is an upper bound on the gluino mass
as m_{\rm gluino} \lsim 1.8 TeV so that the energy density of gravitino does
not exceed the observed dark matter density .Comment: 11 pages, 3 figures. Minor corrections, new references added, to
appear in PL
Reduced Dynamics from the Unitary Group to Some Flag Manifolds : Interacting Matrix Riccati Equations
In this paper we treat the time evolution of unitary elements in the N level
system and consider the reduced dynamics from the unitary group U(N) to flag
manifolds of the second type (in our terminology). Then we derive a set of
differential equations of matrix Riccati types interacting with one another and
present an important problem on a nonlinear superposition formula that the
Riccati equation satisfies.
Our result is a natural generalization of the paper {\bf Chaturvedi et al}
(arXiv : 0706.0964 [quant-ph]).Comment: Latex ; 13 pages ; no figur
The Kondo crossover in shot noise of a single quantum dot with orbital degeneracy
We investigate out of equilibrium transport through an orbital Kondo system
realized in a single quantum dot, described by the multiorbital impurity
Anderson model. Shot noise and current are calculated up to the third order in
bias voltage in the particle-hole symmetric case, using the renormalized
perturbation theory. The derived expressions are asymptotically exact at low
energies. The resulting Fano factor of the backscattering current is
expressed in terms of the Wilson ratio and the orbital degeneracy as
at zero temperature. Then,
for small Coulomb repulsions , we calculate the Fano factor exactly up to
terms of order , and also carry out the numerical renormalization group
calculation for intermediate in the case of two- and four-fold degeneracy
(). As increases, the charge fluctuation in the dot is suppressed,
and the Fano factor varies rapidly from the noninteracting value to the
value in the Kondo limit , near the crossover region
, with the energy scale of the hybridization .Comment: 10 pages, 4 figure
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