Particle Motion with Ho\v{r}ava -- Lifshitz type Dispersion Relations (2009)
Using super Hamiltonian formalism, we study the motion of particles whose dispersion relations are modified to incorporate Ho\v{r}ava -- Lifshitz type anisotropic scaling symmetry. We find the...
Anisotropic Cosmology and (Super)Stiff Matter in Ho\v{r}ava's Gravity Theory (2009)
We study anisotropic cosmology in Ho\v{r}ava's gravity theory and obtain Kasner type solutions, valid for any number d of spatial dimensions. The corresponding exponents satisfy two relations, one...
Bhowmick, Samrat, Digal, Sanatan, Rama, S. Kalyana
Our model consists of intersecting 22'55' brane configuration in M theory, distributed uniformly in the common transverse space and assumed to describe early universe. Equations of state are those...
A Description of Rotating Multicharged Black Holes in terms of Branes and Antibranes (2007)
Bhowmick, Samrat, Rama, S. Kalyana
We describe rotating multicharge black holes as stacks of intersecting branes and antibranes together with massless gases on them. Assuming the energies of the gases to be equal, we find that their...
Consequences of U dualities for Intersecting Branes in the Universe (2007)
We consider N -- charge, intersecting brane antibrane configurations in M theory which are smeared uniformly in the common transverse space and may describe our universe. We study the consequences of...
Entropy of Anisotropic Universe and Fractional Branes (2007)
We obtain the entropy of a homogeneous anisotropic universe applicable, by assumption, to the fractional branes in the universe in the model of Chowdhury and Mathur. The entropy for the 3 or 4 charge...
A Principle to Determine the Number (3 + 1) of Large Spacetime Dimensions (2006)
We assume that our universe originated from highly excited and interacting strings with coupling constant g_s = {\cal O} (1). Fluctuations of spacetime geometry are large in such strings and the...
A Stringy Correspondence Principle in Cosmology (2006)
We study a d-dimensional FRW universe, containing a perfect fluid with p = w \rho and \frac{1} {d - 1} \le w \le 1, and find a correspondence principle similar to that of Horowitz and Polchinski in...
Branes in a Time Dependent Universe (2005)
Long ago, McVittie had found a class of solutions which can be thought of as Schwarzschild black holes in an FRW universe. In recent years they have been studied extensively and generalised to...
Multiparameter Brane Solutions by Boosts, S and T dualities (2005)
We show that the multiparameter (intersecting) brane solutions of string/M theories given in the literature can all be obtained by a suitable combination of boosts in eleven dimension, S and T...
Bagchi, Arjun, Rama, S. Kalyana
We consider scalar tensor theories in D-dimensional spacetime, D \ge 4. They consist of metric and a non minimally coupled scalar field, with its non minimal coupling characterised by a function. The...
A Description of multi Charged Black Holes in terms of Branes and Antibranes (2004)
Rama, S. Kalyana, Siwach, Sanjay
We describe multicharged black holes in terms of branes and antibranes together with multiple copies of gas of massless excitations. Assuming that energies of these copies of gas are all equal, we...
A Description of Schwarzschild Black Holes in terms of Intersecting M-branes and antibranes (2004)
Intersecting M-branes are known to describe multi charged black holes. Using a configuration of such intersecting branes and antibranes, together with massless excitations living on them, we give a...
Asymptotic Density of Open p-brane States with Zero-modes included (2003)
We obtain the asymptotic density of open p-brane states with zero-modes included. The resulting logarithmic correction to the p-brane entropy has a coefficient - \frac{p + 2}{2 p}, and is independent...
Black Hole Entropy from Spin One Punctures (2003)
Kaul, Romesh K., Rama, S. Kalyana
Recent suggestion, that the emission of a quantum of energy corresponding to the asymptotic value of quasinormal modes of a Schwarzschild black hole should be associated with the loss of spin one...
Classical Velocity in kappa-deformed Poincare Algebra and a Maximum Acceleration (2002)
We study the commutators of the kappa-deformed Poincare Algebra (kappaPA) in an arbitrary basis. It is known that the two recently studied doubly special relativity theories correspond to different...
Dynamical Features of Maggiore's Generalised Commutation Relations (2002)
We study the dynamical features of Maggiore's generalised commutation relations. We focus on their generality and, in particular, their dependence on the Hamiltonian H. We derive the generalisation...
No Go Theorem for Self Tuning Solutions With Gauss-Bonnet Terms (2002)
Dasgupta, Samik, Venkatachalapathy, Rajesh, Rama, S. Kalyana
We consider self tuning solutions for a brane embedded in an anti de Sitter spacetime. We include the higher derivative Gauss-Bonnet terms in the action and study singularity free solutions with...
On the Emergence of the Microcanonical Description from a Pure State (2001)
Dass, N. D. Hari, Rama, S. Kalyana, Sathiapalan, B.
We study, in general terms, the process by which a pure state can ``self-thermalize'' and {\em appear} to be described by a microcanonical density matrix. This requires a quantum mechanical version...
We study the dynamical consequences of Maggiore's unique generalised uncertainty principle (GUP). We find that it leads naturally, and generically, to novel consequences. In the high temperature...
In the D = (n + m + 1) dimensional brane world scenario with m compact dimensions, the radion modulus can be stabilised by a massive bulk m-form antisymmetric field. We analyse some of the...
We consider (n + m + 1) dimensional bulk spacetime, containing flat (n + m - 1) dimensional parallel branes, with topology R^{n - 1} \times T^m. We assume that the graviton and an m-form field are...
Tsallis Statistics: Averages and a Physical Interpretation of the Lagrange Multiplier $\beta$ (2000)
Tsallis has proposed a generalisation of the standard entropy, which has since been applied to a variety of physical systems. In the canonical ensemble approach that is mostly used, average energy is...
Supergravity with Self-dual B fields and Instantons in Noncommutative Gauge Theory (1999)
Das, S. R., Rama, S. Kalyana, Trivedi, S. P.
We study Type IIB supergravity in the presence of (euclidean) D3 branes and nonzero self-dual B-fields. We point out that the Einstein frame metric is identical to the full geometry for D3 branes...
A Note on Holographic Principle in models of Extended Inflation type (1999)
We present a simple derivation of an upper bound on the average size of the true vacuum bubbles at the end of inflation, in models of extended inflation type. The derivation uses the inequality that...
On the Role of Chaos in the AdS/CFT Connection (1999)
Rama, S. Kalyana, Sathiapalan, B.
The question of how infalling matter in a pure state forms a Schwarzschild black hole that appears to be at non-zero temperature is discussed in the context of the AdS/CFT connection. It is argued...
Holographic Principle in the Closed Universe : a Resolution with Negative Pressure Matter (1999)
A closed universe containing pressureless dust, more generally perfect fluid matter with pressure-to-density ratio w in the range (1/3, - 1/3), violates holographic principle applied according to the...
Holographic Principle during Inflation and a Lower Bound on Density Fluctuations (1998)
Rama, S. Kalyana, Sarkar, Tapobrata
We apply the holographic principle during the inflationary stage of our universe. Where necessary, we illustrate the analysis in the case of new and extended inflation which, together, typify generic...
The Hagedorn Transition, Deconfinement and the AdS/CFT Correspondence (1998)
Rama, S. Kalyana, Sathiapalan, B.
A connection between the Hagedorn transition in string theory and the deconfinement transition in (non-supersymmetric) Yang-Mills theory is made using the AdS/CFT correspondence. We modify the model...
Matrix Theory Description of Schwarzschild Black Holes in the Regime N >> S (1998)
We study the description of Schwarzschild black holes, of entropy S, within matrix theory in the regime $N \ge S \gg 1$. We obtain the most general matrix theory equation of state by requiring that...
Boosts, Schwarzschild Black Holes and Absorption cross-sections in M theory (1997)
Das, Sumit R., Mathur, Samir D., Rama, S. Kalyana, Ramadevi, P.
$D$ dimensional neutral black strings wrapped on a circle are related to $(D-1)$ dimensional charged black holes by boosts. We show that the boost has to be performed in the covering space and the...
Size of Black Holes through Polymer Scaling (1997)
We imagine the strings on the stretched horizon of any $d$ space-time dimensional black hole to be bits of polymer. Then, proposing an interaction between these bits we obtain the size of the...
Graviton-Dilaton Cosmology (1997)
We show that the evolution of the universe is singularity free in a class of graviton-dilaton models.
Can String Theory Avoid Cosmological Singularities? (1997)
We consider the effective action for strings and describe in detail the evolution of a four dimensional homogeneous isotropic universe with matter included. We find that the evolution, which is...
Early Universe Evolution in Graviton-Dilaton Models (1996)
We present a class of graviton-dilaton models which leads to a singularity free evolution of the universe. We study the evolution of a homogeneous isotropic universe. We follow an approach which...
Singularity Free (Homogeneous Isotropic) Universe in Graviton-Dilaton Models (1996)
We present a class of graviton-dilaton models in which a homogeneous isotropic universe, such as our observed one, evolves with no singularity at any time. Such models may stand on their own as...
F-theory from Dirichlet 3-branes (1996)
Jatkar, Dileep P., Rama, S. Kalyana
Starting from the type IIB Dirichlet 3-brane action, we obtain a Nambu-Goto action. It is interpreted as the world volume action of a fundamental 3-brane, and its target space theory as F-theory. The...
Some Cosmological Consequences of Non Trivial PPN Parameters $\beta$ and $\gamma$ (1995)
We study homogeneous isotropic universe in a graviton-dilaton theory obtained, in a previous paper, by a simple requirement that the theory be able to predict non trivial values for $\beta$ and/or...
Rama, S. Kalyana, Ghosh, Sasanka
We look for a graviton-dilaton theory which can predict non trivial values of the PPN parameters $\beta$ and/or $\gamma$ for a charge neutral point star, without any naked singularity. With the...
Analysing the static, spherically symmetric graviton-dilaton solutions in low energy string and Brans-Dicke theory, we find the following. For a charge neutral point star, these theories cannot...
Alternatives to Einstein's theory of general relativity can be distinguished by measuring the parametrised post Newtonian parameters. Two such parameters $\beta$ and $\gamma$, equal to one in...
Inconsistent Physics in the Presence of Time Machines (1994)
Rama, S. Kalyana, Sen, Siddhartha
We present a scenario in $1 + 1$ and $3 + 1$ dimensional space time which is paradoxical in the presence of a time machine. We show that the paradox cannot be resolved and the scenario has {\em no}...
Cosmological Constant in Low Energy $d = 4$ String Leads to Naked Singularity (1994)
In the sigma model approach, the $\beta$-function equations for non critical strings contain a term which acts like a tree level cosmological constant, $\Lambda$. We analyse the static, spherically...
Symplectic Manifolds, Coherent States and Semiclassical Approximation (1993)
Rajeev, S. G., Rama, S. Kalyana, Sen, Siddhartha
We describe the symplectic structure and Hamiltonian dynamics for a class of Grassmannian manifolds. Using the two dimensional sphere ($S^2$) and disc ($D^2$) as illustrative cases, we write their...
Singularities in Low Energy $d = 4$ Heterotic String and Brans-Dicke Theories (1993)
We present the static, spherically symmetric solutions of the low energy $d = 4$ string. They form a simple generalisation of the Schwarzschild solution and describe the gravitational field of a...
Scenario for Seeding a Singularity in $d = 2$ String Black Hole with Tachyon (1993)
The $d = 2$ string admits a black hole solution and also a singular solution when tachyon back reaction is included. It is of importance to know if the former solution can evolve into a later one. An...
Tachyon Back Reaction on $d = 2$ String Black Hole (1993)
We describe a static solution for $d = 2$ critical string theory including the tachyon $T$ but with its potential $V (T)$ set to zero. This solution thus incorporates tachyon back reaction and, when...
Comments on Witten Invariants of 3-Manifolds for SU(2) and $Z_m$ (1993)
Rama, S. Kalyana, Sen, Siddhartha
The values of the Witten invariants, $I_W$, of the lens space $L(p, 1)$ for SU(2) at level $k$ are obtained for arbitrary $p$. A duality relation for $I_W$ when $p$ and $k$ are interchanged, valid...
Tachyon Splits the (d = 2 String) Black Hole Horizon and Turns it Singular (1993)
We present a static solution for $d = 2$ critical string theory including the tachyon $T$ but not its potential $V(T)$. This solution thus incorporates tachyon back reaction and, when $T = 0$,...
Renormalization of Couplings in Embedded Random Surfaces (1992)
Das, Sumit R., Rama, S. Kalyana
We study the dressing of operators and flows of corresponding couplings in models of {\it embedded} random surfaces. We show that these dressings can be obtained by applying the methods of David and...
Three Manifolds and Graph Invariants (1991)
Rama, S. Kalyana, Sen, Siddhartha
We show how the Turaev--Viro invariant can be understood within the framework of Chern--Simons theory with gauge group SU(2). We also describe a new invariant for certain class of graphs by...
New Special Operators in $W$-Gravity Theories (1991)
We find new special physical operators of $W_3 -$gravity having non trivial ghost sectors. Some of these operators may be viewed as the liouville dressings of the energy operator of the Ising model...