1,631 research outputs found
High Temperature Partition Function of the Rigid String
We find that the high temperature limit of the free energy per unit length
for the rigid string agrees dimensionally with that of the QCD string (unlike
the Nambu-Goto string). The sign, and in fact the phase, do not agree. While
this may be a clue to a string theory of QCD, we note that the problem of the
fourth derivative action makes it impossible for the rigid string to be a
correct description.Comment: 7 page
Path integral evaluation of Dbrane amplitudes
We extend Polchinski's evaluation of the measure for the one-loop closed
string path integral to open string tree amplitudes with boundaries and
crosscaps embedded in Dbranes. We explain how the nonabelian limit of
near-coincident Dbranes emerges in the path integral formalism. We give a
careful path integral derivation of the cylinder amplitude including the
modulus dependence of the volume of the conformal Killing group.Comment: Extended version replacing hep-th/9903184, includes discussion of
nonabelian limit, Latex, 10 page
Dynamical Casimir effect for gravitons in bouncing braneworlds
We consider a two-brane system in a five-dimensional anti-de Sitter
spacetime. We study particle creation due to the motion of the physical brane
which first approaches the second static brane (contraction) and then recedes
from it(expansion). The spectrum and the energy density of the generated
gravitons are calculated. We show that the massless gravitons have a blue
spectrum and that their energy density satisfies the nucleosynthesis bound with
very mild constraints on the parameters. We also show that the Kaluza-Klein
modes cannot provide the dark matter in an anti-de-Sitter braneworld. However,
for natural choices of parameters, backreaction from the Kaluza-Klein gravitons
may well become important. The main findings of this work have been published
in the form of a Letter [R. Durrer and M. Ruser, Phys. Rev. Lett. 99, 071601
(2007), arXiv:0704.0756].Comment: 40 pages, 34 figures, improved and extended version, matches
published versio
Dirichlet Boundary State in Linear Dilaton Background
Dirichlet-branes have emerged as important objects in studying
nonperturbative string theory. It is important to generalize these objects to
more general backgrounds other than the usual flat background. The simplest
case is the linear dilaton condensate. The usual Dirichlet boundary condition
violates conformal invariance in such a background. We show that by switching
on a certain boundary interaction, conformal invariance is restored. An
immediate application of this result is to two dimensional string theory.Comment: 6 pages, harvmac, some remarks are modified and one reference is
added, formulas remain the sam
(In)validity of large N orientifold equivalence
It has been argued that the bosonic sectors of supersymmetric SU(N)
Yang-Mills theory, and of QCD with a single fermion in the antisymmetric (or
symmetric) tensor representation, are equivalent in the limit. If
true, this correspondence can provide useful insight into properties of real
QCD (with fundamental representation fermions), such as predictions [with
O(1/N) corrections] for the non-perturbative vacuum energy, the chiral
condensate, and a variety of other observables. Several papers asserting to
have proven this large N ``orientifold equivalence'' have appeared. By
considering theories compactified on , we show explicitly that
this large N equivalence fails for sufficiently small radius, where our
analysis is reliable, due to spontaneous symmetry breaking of charge
conjugation symmetry in QCD with an antisymmetric (or symmetric) tensor
representation fermion. This theory is also chirally symmetric for small
radius, unlike super-Yang-Mills. The situation is completely analogous to
large-N equivalences based on orbifold projections: simple symmetry realization
conditions are both necessary and sufficient for the validity of the large N
equivalence. Whether these symmetry realization conditions are satisfied
depends on the specific non-perturbative dynamics of the theory under
consideration. Unbroken charge conjugation symmetry is necessary for validity
of the large N orientifold equivalence. Whether or not this condition is
satisfied on (or for sufficiently large radius) is not
currently known.Comment: 23 pages, added discussion of P, T symmetry realizatio
Cosmological implications of an evolutionary quantum gravity
The cosmological implications of an evolutionary quantum gravity are analyzed
in the context of a generic inhomogeneous model. The Schr\"{o}dinger problem is
formulated and solved in the presence of a scalar field, an ultrarelativistic
matter and a perfect gas regarded as the dust-clock. Considering the actual
phenomenology, it is shown how the evolutionary approach overlaps the
Wheeler-DeWitt one.Comment: 4 pages; to appear in the proceedings of the II Stueckelberg
Workshop, Int.J.Mod.Phys.A, references adde
Quantum Kalb-Ramond Field in D-dimensional de Sitter Spacetimes
In this work we investigate the quantum theory of the Kalb-Ramond fields
propagating in dimensional de Sitter spacetimes using the dynamic invariant
method developed by Lewis and Riesenfeld [J. Math. Phys. 10, 1458 (1969)] to
obtain the solution of the time-dependent Schr\"odinger equation. The wave
function is written in terms of a number quantity satisfying of the
Milne-Pinney equation, whose solution can be expressed in terms of two
independent solutions of the respective equation of motion. We obtain the exact
solution for the quantum Kalb-Ramond field in the de Sitter background and
discuss its relation with the Cremmer-Scherk-Kalb-Ramond model
Dual Actions for Born-Infeld and Dp-Brane Theories
Dual actions with respect to U(1) gauge fields for Born-Infeld and -brane
theories are reexamined. Taking into account an additional condition, i.e. a
corollary to the field equation of the auxiliary metric, one obtains an
alternative dual action that does not involve the infinite power series in the
auxiliary metric given by ref. \cite{s14}, but just picks out the first term
from the series formally. New effective interactions of the theories are
revealed. That is, the new dual action gives rise to an effective interaction
in terms of one interaction term rather than infinite terms of different
(higher) orders of interactions physically. However, the price paid for
eliminating the infinite power series is that the new action is not quadratic
but highly nonlinear in the Hodge dual of a -form field strength. This
non-linearity is inevitable to the requirement the two dual actions are
equivalent.Comment: v1: 11 pages, no figures; v2: explanation of effective interactions
added; v3: concision made; v4: minor modification mad
A finite cutoff on the string worldsheet?
D-brane backgrounds are specified in closed string theories by holes with
appropriate mixed Dirichlet and Neumann boundary conditions on the string
worldsheet. As presently stated, the prescription defining D-brane backgrounds
is such that the Einstein equation is not equivalent to the condition for scale
invariance on the string worldsheet. A modified D-brane prescription is found,
that leads to the desired equivalence, while preserving all known D-brane lore.
A possible interpretation is that the worldsheet cutoff is finite. Possible
connections to recent work of Maldacena and Strominger, and Gopakumar and Vafa
are suggested.Comment: 7 pages, RevTex; v2: typos corrected, superstring calculation
included, discussion expanded - to be published in Phys.Rev.
Creation of Fundamental Strings by Crossing D-branes
We study the force balance between orthogonally positioned -brane and
-brane. The force due to graviton and dilaton exchange is repulsive in
this case. We identify the attractive force that balances this repulsion as due
to one-half of a fundamental string stretched between the branes. As the
-brane passes through the -brane, the connecting string changes
direction, which may be interpreted as creation of one fundamental string. We
show this directly from the structure of the Chern-Simons terms in the D-brane
effective actions. We also discuss the effect of string creation on the 0-brane
quantum mechanics in the type I' theory. The creation of a fundamental string
is related by U-duality to the creation of a 3-brane discussed by Hanany and
Witten. Both processes have a common origin in M-theory: as two M5-branes with
one common direction cross, a M2-brane stretched between them is created.Comment: 6 pages, Late
- âŠ