414 research outputs found
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
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
Spontaneous Lorentz Breaking and Massive Gravity
We study a theory where the presence of an extra spin-two field coupled to
gravity gives rise to a phase with spontaneously broken Lorentz symmetry. In
this phase gravity is massive, and the Weak Equivalence Principle is respected.
The newtonian potentials are in general modified, but we identify an
non-perturbative symmetry that protects them. The gravitational waves sector
has a rich phenomenology: sources emit a combination of massless and massive
gravitons that propagate with distinct velocities and also oscillate. Since
their velocities differ from the speed of light, the time of flight difference
between gravitons and photons from a common source could be measured.Comment: 4 page
Determinant-Gravity: Cosmological implications
We analyze the action as a possible alternative or addition to the Einstein gravity.
Choosing a particular form of we can restore the
Einstein gravity and, if , we obtain the cosmological constant
term. Taking and expanding the action in , we obtain as a leading term the Einstein Lagrangian with a cosmological
constant proportional to and a series of higher order operators. In
general case of non-vanishing and new cosmological
solutions for the Robertson-Walker metric are obtained.Comment: revtex format, 5 pages,8 figures,references adde
Flux vacua in DBI type Einstein-Maxwell theory
We study compactification of extra dimensions in a theory of
Dirac-Born-Infeld (DBI) type gravity. We investigate the solution for Minkowski
spacetime with an extra space as well as that for de Sitter spacetime
() with an extra space. They are derived by the effective potential
method in the presence of the magnetic flux on the extra sphere. We also
consider the higher dimensional generalization of the solutions. We find that,
in a certain model, the radius of the extra space has a minimum value
independent of the higher-dimensional Newton constant in weak-field limit.Comment: 13 pages, no figure. A reference added, typos fixe
Hydration and acetylation of limonene. Supported heteropolyacids
The limonene hydration and acetylation in liquid phase catalyzed by phosphotungstic and phosphomolybdic acid bulk and supported on silica and titanium dioxide were studied. The reaction was performed in a batch reactor in acetic acid at 40°C, with magnetic stirring of the reaction mixture. Reaction products were analyzed by gaseous chromatography with FID detector using a capillary column for separation of products. The identification of compounds was made with pattern terpenes and by gaseous chromatography with mass spectrometry. All catalysts tested result to be active in the hydration and acetylation reaction of limonene. Catalysts based on phophotungstic acid (HPW) produce larger amount of hydration and acetylation products than phosphomolybdic acid (HPMo) catalyst. Hydration products increase faster than isomerization products when the reaction time is increased. The structure of heteropolyacids and the presence of acid sites Bronsted and Lewis were determined by FTIR.Centro de Investigación y Desarrollo en Ciencias Aplicada
Electroweak baryogenesis and low energy supersymmetry
Electroweak baryogenesis is an interesting theoretical scenario, which
demands physics beyond the Standard Model at energy scales of the order of the
weak boson masses. It has been recently emphasized that, in the presence of
light stops, the electroweak phase transition can be strongly first order,
opening the window for electroweak baryogenesis in the MSSM. For the
realization of this scenario, the Higgs boson must be light, at the reach of
the LEP2 collider. In this article, we compute the baryon asymmetry assuming
the presence of non-trivial CP violating phases in the parameters associated
with the left-right stop mixing term and the Higgsino mass . We conclude
that a phase and Higgsino and gaugino mass
parameters , and of the order of the electroweak scale, are
necessary in order to generate the observed baryon asymmetry.Comment: 20 pages, latex + psfig, 3 figure
Hydration and acetylation of limonene. Supported heteropolyacids
The limonene hydration and acetylation in liquid phase catalyzed by phosphotungstic and phosphomolybdic acid bulk and supported on silica and titanium dioxide were studied. The reaction was performed in a batch reactor in acetic acid at 40°C, with magnetic stirring of the reaction mixture. Reaction products were analyzed by gaseous chromatography with FID detector using a capillary column for separation of products. The identification of compounds was made with pattern terpenes and by gaseous chromatography with mass spectrometry. All catalysts tested result to be active in the hydration and acetylation reaction of limonene. Catalysts based on phophotungstic acid (HPW) produce larger amount of hydration and acetylation products than phosphomolybdic acid (HPMo) catalyst. Hydration products increase faster than isomerization products when the reaction time is increased. The structure of heteropolyacids and the presence of acid sites Bronsted and Lewis were determined by FTIR.Centro de Investigación y Desarrollo en Ciencias Aplicada
Violations of universality in a vectorlike extension of the standard model
Violations of universality of couplings in a vectorlike extension of the
standard model with three heavy mirror fermion families are considered. The
recently observed discrepancies between experiments and the standard model in
the hadronic branching fractions and of the Z-boson are explained
by the mixing of fermions with their mirror fermion partners.Comment: latex2e, 11 page
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