637 research outputs found
Power Counting and Perturbative One Pion Exchange in Heavy Meson Molecules
We discuss the possible power counting schemes that can be applied in the
effective field theory description of heavy meson molecules, such as the
X(3872) or the recently discovered Zb(10610) and Zb(10650) states. We argue
that the effect of coupled channels is suppressed by at least two orders in the
effective field theory expansion, meaning that they can be safely ignored at
lowest order. The role of the one pion exchange potential between the heavy
mesons, and in particular the tensor force, is also analyzed. By using
techniques developed in atomic physics for handling power-law singular
potentials, which have been also successfully employed in nuclear physics, we
determine the range of center-of-mass momenta for which the tensor piece of the
one pion exchange potential is perturbative. In this momentum range, the one
pion exchange potential can be considered a subleading order correction,
leaving at lowest order a very simple effective field theory consisting only on
contact-range interactions.Comment: 21 pages, 1 figur
Gravitational induced particle production through a nonminimal curvature-matter coupling
We consider the possibility of a gravitationally induced particle production
through the mechanism of a nonminimal curvature-matter coupling. An interesting
feature of this gravitational theory is that the divergence of the
energy-momentum tensor is nonzero. As a first step in our study we reformulate
the model in terms of an equivalent scalar-tensor theory, with two arbitrary
potentials. By using the formalism of open thermodynamic systems, we interpret
the energy balance equations in this gravitational theory from a thermodynamic
point of view, as describing irreversible matter creation processes. The
particle number creation rates, the creation pressure, and the entropy
production rates are explicitly obtained as functions of the scalar field and
its potentials, as well as of the matter Lagrangian. The temperature evolution
laws of the newly created particles are also obtained. The cosmological
implications of the model are briefly investigated, and it is shown that the
late-time cosmic acceleration may be due to particle creation processes.
Furthermore, it is also shown that due to the curvature--matter coupling,
during the cosmological evolution a large amount of comoving entropy is also
produced.Comment: 15 pages; accepted for publication in the European Physical Journal
Stability of inflationary solutions driven by a changing dissipative fluid
In this paper the second Lyapunov method is used to study the stability of
the de Sitter phase of cosmic expansion when the source of the gravitational
field is a viscous fluid. Different inflationary scenarios related with
reheating and decay of mini-blackholes into radiation are investigated using an
effective fluid described by time--varying thermodynamical quantities.Comment: 17 pages, LaTeX 2.09, 2 figures. To be published in Classical and
Quantum Gravit
Dual interacting cosmologies and late accelerated expansion
In this paper we show that by considering a universe dominated by two
interacting components a superaccelerated expansion can be obtained from a
decelerated one by applying a dual transformation that leaves the Einstein's
field equations invariant.Comment: 13 pages, 1 figura, version to match published articl
The Heavy Quark Spin Symmetry Partners of the X(3872)
We explore the consequences of heavy quark spin symmetry for the charmed
meson-antimeson system in a contact-range (or pionless) effective field theory.
As a trivial consequence, we theorize the existence of a heavy quark spin
symmetry partner of the X(3872), with , which we call X(4012) in
reference to its predicted mass. If we additionally assume that the X(3915) is
a heavy spin symmetry partner of the X(3872), we end up predicting a
total of six molecular states. We also discuss the error
induced by higher order effects such as finite heavy quark mass corrections,
pion exchanges and coupled channels, allowing us to estimate the expected
theoretical uncertainties in the position of these new states.Comment: 18 pages; final version accepted for publicatio
Renormalization of NN-Scattering with One Pion Exchange and Boundary Conditions
A non perturbative renormalization scheme for Nucleon-Nucleon interaction
based on boundary conditions at short distances is presented and applied to the
One Pion Exchange Potential. It is free of off-shell ambiguities and
ultraviolet divergences, provides finite results at any step of the calculation
and allows to remove the short distance cut-off in a suitable way. Low energy
constants and their non-perturbative evolution can directly be obtained from
experimental threshold parameters in a completely unique and model independent
way when the long range explicit pion effects are eliminated. This allows to
compute scattering phase shifts which are, by construction consistent with the
effective range expansion to a given order in the C.M. momentum . In the
singlet and triplet channels ultraviolet fixed points
and limit cycles are obtained respectively for the threshold parameters. Data
are described satisfactorily up to CM momenta of about .Comment: 22 pages, 10 figures, revte
Renormalization of the Deuteron with One Pion Exchange
We analyze the deuteron bound state through the One Pion Exchange Potential.
We pay attention to the short distance peculiar singularity structure of the
bound state wave functions in coordinate space and the elimination of short
distance ambiguities by selecting the regular solution at the origin. We
determine the so far elusive amplitude of the converging exponential solutions
at the origin. All bound state deuteron properties can then be uniquely deduced
from the deuteron binding energy, the pion-nucleon coupling constant and pion
mass. This generates correlations among deuteron properties. Scattering phase
shifts and low energy parameters in the 3S1-3D1 channel are constructed by
requiring orthogonality of the positive energy states to the deuteron bound
state, yielding an energy independent combination of boundary conditions. We
also analyze from the viewpoint of short distance boundary conditions the weak
binding regime on the light of long distance perturbation theory and discuss
the approach to the chiral limit.Comment: 22 pages, 11 figure
Cosmological perturbations in warm inflationary models with viscous pressure
Scalar and tensorial cosmological perturbations generated in warm
inflationary scenarios whose matter-radiation fluid is endowed with a viscous
pressure are considered. Recent observational data from the WMAP experiment are
employed to restrict the parameters of the model. Although the effect of this
pressure on the matter power spectrum is of the order of a few percent, it may
be detected in future experiments.Comment: 20 pages, to be published in the Physcal Review
A Quintessence Scalar Field in Brans-Dicke Theory
It is shown that a minimally coupled scalara field in Brans-Dicke theory
yields a non-decelerated expansion for the present universe for open, flat and
closed Friedmann-Robertson-Walker models.Comment: Latex file, 9 pages, no figures; to be published in Classical and
Quantum Gravit
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