750 research outputs found
FRW Cosmological Perturbations in Massive Bigravity
Cosmological perturbations of FRW solutions in ghost free massive bigravity,
including also a second matter sector, are studied in detail. At early time, we
find that sub horizon exponential instabilities are unavoidable and they lead
to a premature departure from the perturbative regime of cosmological
perturbations.Comment: latex, 14 page
Structure Formation with Mirror Dark Matter: CMB and LSS
In the mirror world hypothesis the mirror baryonic component emerges as a
possible dark matter candidate. An immediate question arises: how the mirror
baryons behave and what are the differences from the more familiar dark matter
candidates as e.g. cold dark matter? In this paper we answer quantitatively to
this question. First we discuss the dependence of the relevant scales for the
structure formation (Jeans and Silk scales) on the two macroscopic parameters
necessary to define the model: the temperature of the mirror plasma (limited by
the Big Bang Nucleosynthesis) and the amount of mirror baryonic matter. Then we
perform a complete quantitative calculation of the implications of mirror dark
matter on the cosmic microwave background and large scale structure power
spectrum. Finally, confronting with the present observational data, we obtain
some bounds on the mirror parameter space.Comment: 11 pages, 6 figures; minor corrections, references added; accepted
for publication in IJMP
Spherically Symmetric Solutions in Ghost-Free Massive Gravity
Recently, a class of theories of massive gravity has been shown to be
ghost-free. We study the spherically symmetric solutions in the bigravity
formulation of such theories. In general, the solutions admit both a Lorentz
invariant and a Lorentz breaking asymptotically flat behaviour and also fall in
two branches. In the first branch, all solutions can be found analitycally and
are Schwarzschild-like, with no modification as is found for other classes of
theories. In the second branch, exact solutions are hard to find, and relying
on perturbation theory, Yukawa-like modifications of the static potential are
found. The general structure of the solutions suggests that the bigravity
formulation of massive gravity is crucial and more than a tool.Comment: 15 pages. Some change in the reference
Mean temperature and humidity variations, along with patient age, predict the number of visits for renal colic in a large urban Emergency Department: Results of a 9-year survey
Background: A marked geographic variability has been reported in stone disease, partially attributed to the Mean Annual Temperature (MAT), as well as to the seasonal fluctuations of climatic conditions. Accordingly, peaks in Emergency Department (ED) visits for renal colic are commonplace during the summer.
Materials and methods: The aim of this study was to assess the influence of day-by-day climate changes on the number of visits as a result of renal colic in the ED (City of Parma, northern Italy, temperate continental climate). A total of 10,802 colic episodes were retrieved from the database during a period of 3286 days (January 2002 to December 2010).
Results: The analysis of the data confirms a peak of renal colic cases during the summer, especially in July (maximum number of 4.1 cases of renal colic per day), and a winter nadir (minimum number of 2.7 cases of renal colic per day, in February). The linear regression analysis shows a high and significant correlation between the mean number of cases of renal colic per day and both the mean daily temperature (positive association, R = 0.93; p 70 years of age.
Conclusion: The combined data suggest that the hot and dry climate would favor an acceleration of the process of stone formation, which seems more pronounced in the older population
On the cosmology of massive bigravity
In this note we briefly review the present status of cosmology in massive bigravity. The bottom line is that no stable FLRW cosmology exists at the leading order, showing a breakdown of cosmological perturbation theory much earlier than in GR. A possible way out could be a non-linear treatment
Stars and (Furry) Black Holes in Lorentz Breaking Massive Gravity
We study the exact spherically symmetric solutions in a class of
Lorentz-breaking massive gravity theories, using the effective-theory approach
where the graviton mass is generated by the interaction with a suitable set of
Stuckelberg fields. We find explicitly the exact black hole solutions which
generalizes the familiar Schwarzschild one, which shows a non-analytic hair in
the form of a power-like term r^\gamma. For realistic self-gravitating bodies,
we find interesting features, linked to the effective violation of the Gauss
law: i) the total gravitational mass appearing in the standard 1/r term gets a
multiplicative renormalization proportional to the area of the body itself; ii)
the magnitude of the power-like hairy correction is also linked to size of the
body. The novel features can be ascribed to presence of the goldstones fluid
turned on by matter inside the body; its equation of state approaching that of
dark energy near the center. The goldstones fluid also changes the matter
equilibrium pressure, leading to an upper limit for the graviton mass, m <~
10^-28 - 10^29 eV, derived from the largest stable gravitational bound states
in the Universe.Comment: 22 pages, 4 Figures. Final version to be published in PRD. Typos
corrected, comments adde
Towards a Nonequilibrium Quantum Field Theory Approach to Electroweak Baryogenesis
We propose a general method to compute -violating observables from
extensions of the standard model in the context of electroweak baryogenesis. It
is alternative to the one recently developed by Huet and Nelson and relies on a
nonequilibrium quantum field theory approach. The method is valid for all
shapes and sizes of the bubble wall expanding in the thermal bath during a
first-order electroweak phase transition. The quantum physics of -violation
and its suppression coming from the incoherent nature of thermal processes are
also made explicit.Comment: 19 pages, 1 figure available upon e-mail reques
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