Black holes, compact objects and solar system tests in non-relativistic general covariant theory of gravity

We study spherically symmetric static spacetimes generally filled with an anisotropic fluid in the nonrelativistic general covariant theory of gravity. In particular, we find that the vacuum solutions are not unique, and can be expressed in terms of the $U(1)$ gauge field $A$. When solar system tests are considered, severe constraints on $A$ are obtained, which seemingly pick up the Schwarzschild solution uniquely. In contrast to other versions of the Horava-Lifshitz theory, non-singular static stars made of a perfect fluid without heat flow can be constructed, due to the coupling of the fluid with the gauge field. These include the solutions with a constant pressure. We also study the general junction conditions across the surface of a star. In general, the conditions allow the existence of a thin matter shell on the surface. When applying these conditions to the perfect fluid solutions with the vacuum ones as describing their external spacetimes, we find explicitly the matching conditions in terms of the parameters appearing in the solutions. Such matching is possible even without the presence of a thin matter shell.Comment: Singular behavior of the fluid at the center is clarified. New references are added. Version to appear in JCA

Understanding Gravity: Some Extra Dimensional Perspectives

Gravity is one of the most inexplicable forces of nature, controlling everything, from the expansion of the Universe to the ebb and flow of ocean tides. The search for the laws of motion and gravitation began more than two thousand years ago but still we do not have the complete picture of it. In this article, we have outlined how our understanding of gravity is changing drastically with time and how the previous explanations have shaped the most recent developments in the field like superstrings and braneworlds.Comment: 21 page

Plasmon Annihilation into Kaluza-Klein Graviton: New Astrophysical Constraints on Large Extra Dimensions

In large extra dimensional Kaluza-Klein (KK) scenario, where the usual Standard Model (SM) matter is confined to a 3+1-dimensional hypersurface called the 3-brane and gravity can propagate to the bulk (D=4+d, d being the number of extra spatial dimensions), the light graviton KK modes can be produced inside the supernova core due to the usual nucleon-nucleon bremstrahlung, electron-positron and photon-photon annihilations. This photon inside the supernova becomes plasmon due to the plasma effect. In this paper, we study the energy-loss rate of SN 1987A due to the KK gravitons produced from the plasmon-plasmon annihilation. We find that the SN 1987A cooling rate leads to the conservative bound $M\_D$ > 22.9 TeV and 1.38 TeV for the case of two and three space-like extra dimensions.Comment: 13 pages, 1 ps figure, text is modified a little bit, conclusion unchanged, new references are added, version accepted for publication in PR

First Record of Regular Sea Urchin Salmacis virgulata (L. Agassiz and Desor 1846) from the Pondicherry Coast, India

The paper reported the first record of Regular sea urchin Salmacis virgulata (L. Agassiz and Desor 1846) in the Pondicherry coast, India. Three adult specimens were found in Kalapet region of Pondicherry coast, India in May 2010. It is a characteristic organism of the Echinoderm fauna of the Bay of Bengal and the description of the organism are provide

Mangrove vegetation and community structure of brachyuran crabs as ecological indicators of Pondicherry coast, South east coast of India

Baseline ecological studies of Pondicherry mangroves are important for monitoring, management and conservation of mangrove ecosystems. A brachyuran crab faunal assemblage at four stations of Pondicherry mangroves is described and monthly samplings were made during September 2008 – August 2009. Totally 22 species of brachyuran crabs belonging to 12 genera and 5 families were recorded; crabs belonging to the family Portunidae and Ocipodidae are most dominant group represented by total of 16 species. Six species considered are as a commercially important and out of which, on three species Scylla serrata, Thalamitta crenata and Portunus sanguinolentus are catch large quantities from stations 1 and 2. Portunus pelagicus, P. sanguinolentus and T. crenata were totally absent in stations 3 and 4. Population densities of brachyuran fauna ranged from 29 -71 ind. m2, the diversity ranged from 0.96 -2.18 bit. ind -1, the richness varied from 0.42 -0.74, and the evenness varied from 0.41 -.072. Maximum diversity values were recorded during post monsoon. The crab community recorded was analyzed by univariate and multivariate statistical techniques. Crab community structure was correlated with vegetation structure, and environmental factors were positively correlated with surface water pH, salinity, tree dominance, tree diversity and tidal inundation and negatively correlated with sulphide, organic matter, senescent leaves and decaying leaves, suggesting that the mangrove vegetation is important to the crab fauna as a habitat and food supply