629 research outputs found
Interacting quintessence and the coincidence problem
We investigate the role of a possible coupling of dark matter and dark
energy. In particular, we explore the consequences of such an interaction for
the coincidence problem, i.e., for the question, why the energy densities of
dark matter and dark energy are of the same order just at the present epoch. We
demonstrate, that, with the help of a suitable coupling, it is possible to
reproduce any scaling solution , where is the
scale factor of the Robertson-Walker metric and is a constant parameter.
and are the densities of dark energy and dark matter,
respectively. Furthermore, we show that an interaction between dark matter and
dark energy can drive the transition from an early matter dominated era to a
phase of accelerated expansion with a stable, stationary ratio of the energy
densities of both components.Comment: 3 pages, contribution to the Tenth Marcel Grossmann Meeting, Rio de
Janeiro, 20-26 July 200
Stochastic mechanics and the Feynman integral
The Feynman integral is given a stochastic interpretation in the framework of Nelson's stochastic mechanics employing a time-symmetric variant of Nelson's kinematics recently developed by the author
Unitarity of the Leptonic Mixing Matrix
We determine the elements of the leptonic mixing matrix, without assuming
unitarity, combining data from neutrino oscillation experiments and weak
decays. To that end, we first develop a formalism for studying neutrino
oscillations in vacuum and matter when the leptonic mixing matrix is not
unitary. To be conservative, only three light neutrino species are considered,
whose propagation is generically affected by non-unitary effects. Precision
improvements within future facilities are discussed as well.Comment: Standard Model radiative corrections to the invisible Z width
included. Some numerical results modified at the percent level. Updated with
latest bounds on the rare tau decay. Physical conculsions unchange
Renormalization of chiral two pion exchange NN interactions with delta excitations: correlations in the partial wave expansion
In this work we consider the renormalization of the chiral two-pion exchange
potential with explicit delta-excitations for nucleon-nucleon scattering at
next-to-leading (NLO) and next-to-next-to-leading order (N2LO). Due to the
singular nature of the chiral potentials, correlations between different
partial waves are generated. In particular we show that two-body scattering by
a short distance power like singular attractive interaction can be renormalized
in all partial waves with a single counterterm, provided the singularities are
identical. A parallel statement holds in the presence of tensor interactions
when the eigenpotentials in the coupled channel problem also coincide. While
this construction reduces the total number of counterterms to eleven in the
case of nucleon-nucleon scattering with chiral two-pion exchange interactions
with delta degrees of freedom, the differences in the scattering phases as
compared to the case with the uncorrelated partial wave renormalization become
smaller as the angular momentum is increased in the elastic scattering region.Comment: 20 pages, 8 figures, a section has been added discussing cut-off
dependence. Accepted for publication in PR
Predicting the baryon asymmetry with degenerate right-handed neutrinos
We consider the generation of a baryon asymmetry in an extension of the
Standard Model with two singlet Majorana fermions that are degenerate above the
electroweak phase transition. The model can explain neutrino masses as well as
the observed matter-antimatter asymmetry, for masses of the heavy singlets
below the electroweak scale. The only physical CP violating phases in the model
are those in the PMNS mixing matrix, i.e. the Dirac phase and a Majorana phase
that enter light neutrino observables. We present an accurate analytic
approximation for the baryon asymmetry in terms of CP flavour invariants, and
derive the correlations with neutrino observables. We demonstrate that the
measurement of CP violation in neutrino oscillations as well as the mixings of
the heavy neutral leptons with the electron, muon and tau flavours suffice to
pin down the matter-antimatter asymmetry from laboratory measurements.Comment: 29 + 4 pages, 9 figures. Includes a comparison to the non-degenerate
scenario. Matches published version in JHE
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