20,111 research outputs found
One-loop Evolution of a Rolling Tachyon
We study the time evolution of the one-loop diagram in Sen's rolling tachyon
background. We find that at least in the long cylinder case they grow rapidly
at late time, due to the exponential growth of the timelike oscillator terms in
the boundary state. This can also be interpreted as the virtual open string
pair creation in the decaying brane. This behavior indicates a breakdown of
this rolling tachyon solution at some point during the evolution. We also
discuss the closed string emission from this one-loop diagram, and the
evolution of a one-loop diagram connecting a decaying brane to a stable brane,
which is responsible for the physical open string creation on the stable brane.Comment: 21 pages, 2 figures; v2: references added, comments revised in
various places; v3: footnotes 7&8 added, revised version to appear in PR
Tachyon Tube on non BPS D-branes
We report our searches for a single tubular tachyonic solution of regular
profile on unstable non BPS D3-branes. We first show that some extended
Dirac-Born-Infeld tachyon actions in which new contributions are added to avoid
the Derrick's no-go theorem still could not have a single regular tube
solution. Next we use the Minahan-Zwiebach tachyon action to find the regular
tube solutions with circular or elliptic cross section. With a critical
electric field, the energy of the tube comes entirely from the D0 and strings,
while the energy associated to the tubular D2-brane tension is vanishing. We
also show that fluctuation spectrum around the tube solution does not contain
tachyonic mode. The results are consistent with the identification of the
tubular configuration as a BPS D2-brane.Comment: Latex 18 page
Exact Black Hole Degeneracies and the Topological String
Motivated by the recent conjecture of Ooguri, Strominger and Vafa, we compute
the semi-canonical partition function of BPS black holes in N=4 and N=8 string
theories, to all orders in perturbation theory. Not only are the black hole
partition functions surprisingly simple; they capture the full topological
string amplitudes, as expected from the OSV conjecture. The agreement is not
perfect, however, as there are differences between the black hole and
topological string partition functions even at the perturbative level. We
propose a minimal modification of the OSV conjecture, in which these
differences are understood as a nontrivial measure factor for the topological
string.Comment: 24 page
Black Hole Entropy in the presence of Chern-Simons Terms
We derive a formula for the black hole entropy in theories with gravitational
Chern-Simons terms, by generalizing Wald's argument which uses the Noether
charge. It correctly reproduces the entropy of three-dimensional black holes in
the presence of Chern-Simons term, which was previously obtained via indirect
methods.Comment: v2: 12 pages, added reference
Chemical Beneficiation of Indian Chromites
The authors here deal with preliminary tests on two samples of Indian chromites for their chemical bene-ficiation. One was from Nausa-hi, Orissa, and the other from Mysore. The ores contained only a little heamatite but no magnetite. Tale was the main gangue material in the former and chlorite was the only gangue in the latter. The first ore(-7 mesh) was reduced at different temperatures using coal, coke, charcoal and coke-oven gas. The second (-7 mesh) ore was reduced at different temperatures with coke-oven gas with or without pre-oxidation
5D Black Holes and Strings with Higher Derivatives
We find asymptotically flat black hole and string solutions to 5D
supergravity in the presence of higher derivative terms. In some cases,
including the fundamental heterotic string solution, the higher derivative
terms smooth out naked singularities into regular geometries carrying zero
entropy. We also compute corrections to the entropy of 5D Calabi-Yau black
holes, and discuss the relation to previous results.Comment: 33 pages, 2 figs., harvmac; v2: typos corrected, references added v3:
refs correcte
Loop Variables and Gauge Invariance in (Open) Bosonic String Theory
We give a simplified and more complete description of the loop variable
approach for writing down gauge invariant equations of motion for the fields of
the open string. A simple proof of gauge invariance to all orders is given. In
terms of loop variables, the interacting equations look exactly like the free
equations, but with a loop variable depending on an extra parameter, thus
making it a band of finite width. The arguments for gauge invariance work
exactly as in the free case. We show that these equations are Wilsonian RG
equations with a finite world-sheet cutoff and that in the infrared limit,
equivalence with the Callan-Symanzik -functions should ensure that they
reproduce the on-shell scattering amplitudes in string theory. It is applied to
the tachyon-photon system and the general arguments for gauge invariance can be
easily checked to the order calculated. One can see that when there is a finite
world sheet cutoff in place, even the U(1) invariance of the equations for the
photon, involves massive mode contributions. A field redefinition involving the
tachyon is required to get the gauge transformations of the photon into
standard form.Comment: 20 pages, Late
The alpha-prime stretched horizon in the Heterotic string
The linear alpha-prime corrections and the field redefinition ambiguities are
studied for half-BPS singular backgrounds representing a wrapped fundamental
string. It is showed that there exist schemes in which the inclusion of all the
linear alpha-prime corrections converts these singular solutions to black holes
with a regular horizon for which the modified Hawking-Bekenstein entropy is in
agreement with the statistical entropy.Comment: 22 pages JHEP; new discussions and more details added to section
Genuine Multiparty Quantum Entanglement Suppresses Multiport Classical Information Transmission
We establish a universal complementarity relation between the capacity of
classical information transmission by employing a multiparty quantum state as a
multiport quantum channel, and the genuine multipartite entanglement of the
quantum state. The classical information transfer is from a sender to several
receivers by using the quantum dense coding protocol with the multiparty
quantum state shared between the sender and the receivers. The relation holds
for arbitrary pure or mixed quantum states of an arbitrary number of parties in
arbitrary dimensions.Comment: 5 (+ epsilon) pages, 2 figures, Revtex4-1; v2: Theorem 3 extended to
all states, other results unchange
Local cosmic string in generalised scalar tensor theory
A recent investigation shows that a local gauge string with a
phenomenological energy momentum tensor, as prescribed by Vilenkin, is
inconsistent in Brans-Dicke theory. In this work it has been shown that such a
string is consistent in a more general scalar tensor theory where is
function of the scalar field.A set of solutions of full nonlinear Einstein's
equations for interior region of such a string are presented.Comment: 7 pages, latex format, minor changes according to referee's
suggestions, revised version submitted in Phys.Rev.
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