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 $CP$-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 $CP$-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