Using an exact supergravity solution representing the D p −D p system, it is demonstrated that one can construct a supergravity analogue of the tachyon potential. Remarkably, the (regularized) minimum value of the potential turns out to be V (T 0 ) = −2m with m denoting the ADM mass of a single D p -brane. This result, in a sense, appears to confirm that Sen's conjecture for the tachyon condensation on unstable Dbranes is indeed correct although the analysis used here is semi-classical in nature and hence should be taken with some care. Also shown is the fact that the tachyon mass squared m 2 T (which has started out as being negative) can actually become positive definite and large as the tachyon rolls down toward the minimum of its potential. It indeed signals the possibility of successful condensation of the tachyon since it shows that near the minimum of its potential, tachyon can become heavy enough to disappear from the massless spectrum. Some cosmological implications of this tachyon potential in the context of "rolling tachyons" is also discussed.
The simplest and the most straightforward new algorithm for generating solutions to (anti) self-dual Yang-Mills (YM) equation in the typical gravitational instanton backgrounds is proposed. When applied to the Taub-NUT and the Eguchi-Hanson metrics, the two best-known gravitational instantons, the solutions turn out to be the rather exotic type of instanton configurations carrying finite YM action but generally fractional topological charge values.PACS numbers: 11.15.-q, 04.40.-b, 04.60.-m
In association with the Blanford-Znajek mechanism for rotational energy extraction from Kerr black holes, it is of some interest to explore how much of magnetic flux can actually penetrate the horizon at least in idealized situations. For completely uncharged Kerr hole case, it has been known for some time that the magnetic flux gets entirely expelled when the hole is maximally-rotating. In the mean time, it is known that when the rotating hole is immersed in an originally uniform magnetic field surrounded by an ionized interstellar medium (plasma), which is a more realistic situation, the hole accretes certain amount of electric charge. In the present work, it is demonstrated that as a result of this accretion charge small enough not to disturb the geometry, the magnetic flux through this slightly charged Kerr hole depends not only on the hole's angular momentum but on the hole's charge as well such that it never vanishes for any value of the hole's angular *
In this work, the interaction of electromagnetic fields with a rotating (Kerr) black hole is explored in the context of Born-Infeld (BI) theory of electromagnetism instead of standard Maxell theory and particularly BI theory versions of the four horizon boundary conditions of Znajek and Damour are derived.Naturally, an issue to be addressed is then whether they would change from the ones given in the Maxwell theory context and if they would, how. Interestingly enough, as long as one employs the same local null tetrad frame as the one adopted in the works by Damour and by Znajek to read out physical values of electromagnetic fields and fictitious surface charge and currents on the horizon, it turns out that one ends up with exactly the same four horizon boundary conditions despite the shift of the electrodynamics theory from a linear Maxwell one to a highly non-linear BI one. Close inspection reveals that this curious and unexpected result can be attributed to the fact that the *
In the present work, perhaps the simplest and the most straightforward new algorithm for generating solutions to the ͑anti-͒self-dual Yang-Mills ͑YM͒ equation in the typical gravitational instanton background is proposed and then applied to find solutions to practically all the known gravitational instantons. The solutions thus obtained turn out to be some kind of instanton-meron hybrids possessing mixed features of both. Namely, they are rather exotic type configurations obeying a first order ͑anti-͒self-dual YM equation which are everywhere nonsingular and have finite Euclidean YM actions on one hand while exhibiting meronlike large distance behavior and carrying generally fractional topological charge values on the other. Close inspection, however, reveals that the solutions are more like instantons than merons in their generic nature.
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