Sukanta Bose

On the Brown-York quasilocal energy, gravitational charge, and black hole horizons

We study a recently proposed horizon defining identity for certain black hole spacetimes. It relates the difference of the Brown-York quasilocal energy and the Komar charge at the horizon to the total energy of the spacetime. The Brown-York quasilocal energy is evaluated for some specific choices of spacetime foliations. With a certain condition imposed on the matter distribution, we prove this identity for spherically symmetric static black hole solutions of general relativity. For these cases, we show that the identity can be derived from a Gauss-Codacci condition that any three-dimensional timelike boundary embedded around the hole must obey. We also demonstrate the validity of the identity in other cases by explicitly applying it to several static, non-static, asymptotically flat, and asymptotically non-flat black hole solutions. These include the asymptotically FRW solutions and the case of a black hole with a global monopole charge.

New classes of black hole spacetimes in 2+1 gravity

Abstract The electrogravity transformation is applied to the three-dimensional Einstein field equations to obtain new multi-parameter families of black hole solutions. The Banados–Teitelboim–Zanelli black hole is shown to be a special case of one of these families. The causal structure, associated matter, as well as the mechanical and thermodynamical properties of some of the solutions are discussed.

Behavior of quasilocal mass under conformal transformations

We show that in a generic scalar-tensor theory of gravity, the ``referenced quasilocal mass of a spatially bounded region in a classical solution is invariant under conformal transformations of the spacetime metric. We first extend the Brown-York quasilocal formalism to such theories to obtain the ``unreferenced quasilocal mass and prove it to be conformally invariant. However, this quantity is typically divergent. It is, therefore, essential to subtract from it a properly defined reference term to obtain a finite and physically meaningful quantity, namely, the referenced quasilocal mass. The appropriate reference term in this case is defined by generalizing the Hawking-Horowitz prescription, which was originally proposed for general relativity. For such a choice of reference term, the referenced quasilocal mass for a general spacetime solution is obtained. This expression is shown to be a conformal invariant provided the conformal factor is a monotonic function of the scalar field. We apply this expression to the case of static spherically symmetric solutions with arbitrary asymptotics to obtain the referenced quasilocal mass of such solutions. Finally, we demonstrate the conformal invariance of our quasilocal mass formula by applying it to specific cases of four-dimensional charged black hole spacetimes, of both the asymptotically flat and non-flat kinds, in conformally related theories.

Exact solutions in two-dimensional string cosmology with back reaction

We present analytic cosmological solutions in a model of two-dimensional dilaton gravity with back reaction. One of these solutions exhibits a graceful exit from the inflationary to the FRW phase and is nonsingular everywhere. A duality related second solution is found to exist only in the {open_quotes}pre-big-bang{close_quotes} epoch and is singular at {tau}=0. In either case back reaction is shown to play a crucial role in determining the specific nature of these geometries. thinsp {copyright} {ital 1997} {ital The American Physical Society}

Quasilocal energy for rotating charged black hole solutions in general relativity and string theory

We explore the (non-)universality of Martinezs conjecture, originally proposed for Kerr black holes, within and beyond general relativity. The conjecture states that the Brown-York quasilocal energy at the outer horizon of such a black hole reduces to twice its irreducible mass, or equivalently, to

Solving the Graceful Exit Problem in Superstring Cosmology

sqrt{A}/2sqrt{ensuremath{pi}},

The electrogravity transformation and global monopoles in scalar-tensor gravity

where A is its area. We first consider the charged Kerr black hole. For such a spacetime, we calculate the quasilocal energy within a two-surface of constant Boyer-Lindquist radius embedded in a constant stationary-time slice. Keeping with Martinezs conjecture, at the outer horizon this energy equals

Erratum to: “The electrogravity transformation and global monopoles in scalar-tensor gravity”: [Phys. Lett. B 488 (2000) 1–10]

sqrt{A}/2sqrt{ensuremath{pi}}.

Lorentzian approach to black hole thermodynamics in the Hamiltonian formulation

The energy is positive and monotonically decreases to the ADM mass as the boundary-surface radius diverges. Next we perform an analogous calculation for the quasilocal energy for the Kerr-Sen spacetime, which corresponds to four-dimensional rotating charged black hole solutions in heterotic string theory. The behavior of this energy as a function of the boundary-surface radius is similar to the charged Kerr case. However, we show that it does not approach the expression conjectured by Martinez at the horizon.

Detection of gravitational waves using a network of detectors

We briefly review the status of the “graceful exit” problem in superstring cosmology and present a possible resolution. It is shown that there exists a solution to this problem in two-dimensional dilaton gravity provided quantum corrections are incorporated. This is similar to the recently proposed solution of Rey. However, unlike in his case, in our one-loop corrected model the graceful exit problem is solved for any finite number of massless scalar matter fields present in the theory.