111 research outputs found
Induction and suppression of an autoimmune disease by oligomerized T cell epitopes: enhanced in vivo potency of encephalitogenic peptides
T cell epitope peptides derived from proteolipid protein (PLP139-151) or myelin basic protein (MBP86-100) induce experimental autoimmune encephalomyelitis (EAE) in "susceptible" strains of mice (e.g., SJL/J). In this study, we show that the encephalitogenic effect of these epitopes when injected subcutaneously in complete Freund's adjuvant was significantly enhanced if administered to the animal in a multimerized form as a T cell epitope oligomer (i.e., as multiple repeats of the peptide epitope, such as 16-mers). Oligomer-treated SJL/J mice developed EAE faster and showed a more severe progression of the disease than animals treated with peptide alone. In addition, haplotype-matched B10.S mice, "resistant" to EAE induction by peptide, on injection of 16-mers developed a severe form of EAE. Even more striking, however, was the dramatic suppression of incidence and severity of the disease, seen after single intravenous injections of only 50 microg of the PLP139-151 16-mer, administered to SJL/J mice 7 d after the induction of the disease. Although relapse occurred at about day 45, an additional injection several days before that maintained the suppression. Importantly, the specific suppressive effect of oligomer treatment was also evident if EAE was induced with spinal cord homogenate instead of the single peptide antigen. By contrast, the PLP139-151 peptide accelerated rather than retarded the progression of disease
The stringy nature of the 2d type-0A black hole
We investigate the thermodynamics of the RR charged two-dimensional type-0A
black hole background at finite temperature, and compare with known 0A matrix
model results. It has been claimed that there is a disagreement for the free
energy between the spacetime and the dual matrix model. Here we find that this
discrepancy is sensitive to how the cutoff is implemented on the spacetime
side. In particular, the disagreement is resolved once we put the cutoff at a
fixed distance away from the horizon, as opposed to a fixed position in space.
Furthermore, the mass and the entropy of the black hole itself add up to an
analytic contribution to the free energy, which is precisely reproduced by the
0A matrix model. We also use results from the 0A matrix model to predict the
next to leading order contribution to the entropy of the black hole. Finally,
we note that the black hole is characterized by a Hagedorn growth in its
density of states below the Hagedorn temperature. This, together with other
results, suggests there is a phase transition at this temperature.Comment: 1+21 pages; v2: Substantial changes in the body of the paper, main
results the same. Clarified discussion on the thermodynamics, added section
on a phase transition, references added. v3: Typos corrected. v4: Final
version, to appear in JHE
Large N limit of Extremal Non-supersymmetric Black Holes
The large N limit of extremal non-supersymmetric Type-I five-dimensional
string black holes is studied from the point of view of D-branes.
We find that the agreement between the D-brane and the black-hole picture is
due to an asymptotic restoration of supersymmetry in the large limit in
which both pictures are compared.
In that limit Type-I string perturbation theory is effectively embedded into
a Type-IIB perturbation theory with unbroken supersymmetric charges whose
presence guarantees the non-renormalization of mass and entropy as the
effective couplings are increased. In this vein, we also study the near-horizon
geometry of the Type-I black hole using D5-brane probes to find that the low
energy effective action for the probe is identical to the corresponding one in
the auxiliary Type-IIB theory in the large N limit.Comment: 25 pages, harvmac, typos corrected and references adde
Decaying D-branes and Moving Mirrors
We present an exact time-dependent solution to the effective D-brane
world-volume theory which describes an inhomogeneous decay of a brane-antibrane
system. We compute the quantum energy flux induced by the particle creation in
this inhomogeneous and time-dependent background. We find that this calculation
is essentially equivalent to that of the moving mirror system. In the initial
stage, the energy flux turns out to be thermal with the temperature given by
the inverse of the distance between the brane and the antibrane. Later it
changes its sign and becomes a negative energy flux. Our result may be relevant
for the (p)reheating process or/and the evolution of cosmic string network
after stringy brane inflation.Comment: 26pages, 4 figures, Latex, typos correcte
Remarks on the rolling tachyon BCFT
It is shown how the boundary correlators of the Euclidean theory
corresponding to the rolling tachyon solution can be calculated directly from
Sen's boundary state. The resulting formulae reproduce precisely the expected
perturbative open string answer. We also determine the open string spectrum and
comment on the implications of our results for the timelike theory.Comment: 20 pages, harvmac(b), no figure
Symmetries at stationary Killing horizons
It has often been suggested (especially by Carlip) that spacetime symmetries
in the neighborhood of a black hole horizon may be relevant to a statistical
understanding of the Bekenstein-Hawking entropy. A prime candidate for this
type of symmetry is that which is exhibited by the Einstein tensor. More
precisely, it is now known that this tensor takes on a strongly constrained
(block-diagonal) form as it approaches any stationary, non-extremal Killing
horizon. Presently, exploiting the geometrical properties of such horizons, we
provide a particularly elegant argument that substantiates this highly
symmetric form for the Einstein tensor. It is, however, duly noted that, on
account of a "loophole", the argument does fall just short of attaining the
status of a rigorous proof.Comment: 11 pages, Revte
Casimir Effect of Graviton and the Entropy Bound
In this note we calculate the Casimir effect of free thermal gravitons in
Einstein universe and discuss how it changes the entropy bound condition
proposed recently by Verlinde [hep-th/0008140] as a higher dimensional
generalization of Cardy's formula for conformal field theories (CFT). We find
that the graviton's Casimir effect is necessary in order not to violate
Verlinde's bound for weakly coupled CFT. We also comment on the implication of
this new Cardy's formula to the thermodynamics of black -brane.Comment: 10 pages; v2. a typo correcte
Holographic Central Charge for 2-Dimensional de Sitter Space
Recently, investigations have begun into a holographic duality for
two-dimensional de Sitter space. In this paper, we evaluate the associated
central charge, using a modified version of the canonical Hamiltonian method
that was first advocated by Catelani {\it et al}. Our computation agrees with
that of a prior work (Cadoni {\it et al}), but we argue that the method used
here is, perhaps, aesthetically preferable on holographic grounds. We also
confirm an agreement between the Cardy and thermodynamic entropy, thus
providing further support for the conjectured two-dimensional de
Sitter/conformal field theory correspondence.Comment: 19 pages, Latex; discussion (Section 4) and references adde
On Minisuperspace Models of S-branes
In this note we reconsider the minisuperspace toy models for rolling and
bouncing tachyons. We show that the theories require to choose boundary
conditions at infinity since particles in an exponentially unbounded potential
fall to infinity in finite world-sheet time. Using standard techniques from
operator theory, we determine the possible boundary conditions and we compute
the corresponding energy spectra and minisuperspace 3-point functions. Based on
this analysis we argue in particular that world-sheet models of S-branes
possess a discrete spectrum of conformal weights containing both positive and
negative values. Finally, some suggestions are made for possible relations with
previous studies of the minisuperspace theory.Comment: 24 pages, 3 figure
Energy Quantisation in Bulk Bouncing Tachyon
We argue that the closed string energy in the bulk bouncing tachyon
background is to be quantised in a simple manner as if strings were trapped in
a finite time interval. We discuss it from three different viewpoints; (1) the
timelike continuation of the sinh-Gordon model, (2) the dual matrix model
description of the (1+1)-dimensional string theory with the bulk bouncing
tachyon condensate, (3) the c_L=1 limit of the timelike Liouville theory with
the dual Liouville potential turned on. There appears to be a parallel between
the bulk bouncing tachyon and the full S-brane of D-brane decay. We find the
critical value \lambda_c of the bulk bouncing tachyon coupling which is
analogous to \lambda_o=1/2 of the full S-brane coupling, at which the system is
thought to be at the bottom of the tachyon potential.Comment: 25 pages, minor changes, one reference adde
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