492 research outputs found
Large N reduction on group manifolds
We show that the large N reduction holds on group manifolds. Large N field
theories defined on group manifolds are equivalent to some corresponding matrix
models. For instance, gauge theories on S^3 can be regularized in a gauge
invariant and SO(4) invariant manner.Comment: 21 pages, 4 figures, typos corrected, a reference adde
Inflation from D3-brane motion in the background of D5-branes
We study inflation arising from the motion of a BPS D3-brane in the
background of a stack of k parallel D5-branes. There are two scalar fields in
this set up-- (i) the radion field R, a real scalar field, and (ii) a complex
tachyonic scalar field chi living on the world volume of the open string
stretched between the D3 and D5 branes. We find that inflation is realized by
the potential of the radion field, which satisfies observational constraints
coming from the Cosmic Microwave Background. After the radion becomes of order
the string length scale l_s, the dynamics is governed by the potential of the
complex scalar field. Since this field has a standard kinematic term, reheating
can be successfully realized by the mechanism of tachyonic preheating with
spontaneous symmetry breaking.Comment: 10 pages, 4 figures. Minor clarifications and references added.
Version to appear in Phys. Rev.
Loop quantum gravity effects on inflation and the CMB
In loop quantum cosmology, the universe avoids a big bang singularity and
undergoes an early and short super-inflation phase. During super-inflation,
non-perturbative quantum corrections to the dynamics drive an inflaton field up
its potential hill, thus setting the initial conditions for standard inflation.
We show that this effect can raise the inflaton high enough to achieve
sufficient e-foldings in the standard inflation era. We analyze the
cosmological perturbations generated when slow-roll is violated after
super-inflation, and show that loop quantum effects can in principle leave an
indirect signature on the largest scales in the CMB, with some loss of power
and running of the spectral index.Comment: revtex4, 5 pages, 3 figures, significant improvements in explanation
of quantization and perturbation issues; version to appear Classical and
Quantum Gravit
A Dilatonic Deformation of AdS_5 and its Field Theory Dual
We find a nonsupersymmetric dilatonic deformation of geometry as an
exact nonsingular solution of the type IIB supergravity. The dual gauge theory
has a different Yang-Mills coupling in each of the two halves of the boundary
spacetime divided by a codimension one defect. We discuss the geometry of our
solution in detail, emphasizing the structure of the boundary, and also study
the string configurations corresponding to Wilson loops. We also show that that
the background is stable under small scalar perturbations.Comment: 19 pages, 8 figures, v2 minor changes, added references, version to
appear in JHE
Power-law behavior in the power spectrum induced by Brownian motion of a domain wall
We show that Brownian motion of a one-dimensional domain wall in a large but
finite system yields a power spectrum. This is successfully
applied to the totally asymmetric simple exclusion process (TASEP) with open
boundaries. An excellent agreement between our theory and numerical results is
obtained in a frequency range where the domain wall motion dominates and
discreteness of the system is not effective.Comment: 4 pages, 4 figure
Summing Up All Genus Free Energy of ABJM Matrix Model
The localization technique allows us to compute the free energy of the U(N)_k
x U(N)_{-k} Chern-Simons-matter theory dual to type IIA strings on AdS_4 x CP^3
from weak to strong 't Hooft coupling \lambda = N / k at finite N, as
demonstrated by Drukker, Marino, and Putrov. In this note we study further the
free energy at large 't Hooft coupling with the aim of testing AdS/CFT at the
quantum gravity level and, in particular, sum up all the 1/N corrections, apart
from the worldsheet instanton contributions. The all genus partition function
takes a remarkably simple form -- the Airy function, Ai (k^{4/3} \lambda_r),
with the renormalized 't Hooft coupling \lambda_r.Comment: 18 pages, no figures, v2: typos corrected and references adde
Is the brick-wall model unstable for a rotating background?
The stability of the brick wall model is analyzed in a rotating background.
It is shown that in the Kerr background without horizon but with an inner
boundary a scalar field has complex-frequency modes and that, however, the
imaginary part of the complex frequency can be small enough compared with the
Hawking temperature if the inner boundary is sufficiently close to the horizon,
say at a proper altitude of Planck scale. Hence, the time scale of the
instability due to the complex frequencies is much longer than the relaxation
time scale of the thermal state with the Hawking temperature. Since ambient
fields should settle in the thermal state in the latter time scale, the
instability is not so catastrophic. Thus, the brick wall model is well defined
even in a rotating background if the inner boundary is sufficiently close to
the horizon.Comment: Latex, 17 pages, 1 figure, accepted for publication in Phys. Rev.
Anomalous negative excursion of carbon isotope in organic carbon after the last Paleoproterozoic glaciation in North America
Early Paleoproterozoic time (2.5–2.0 Ga) spanned a critical phase in Earth's history, characterized by repeated glaciations and an increase in atmospheric oxygen (the Great Oxidation Event (GOE)). Following the last and most intense glaciation of this period, marine carbonates record a large positive excursion of δ^(13)C value (termed the “Lomagundi event”) between about 2.2 and 2.1 Ga coinciding with the global appearances of red beds and sulfates, which suggest an accumulation of high levels of atmospheric oxygen. Here we report the discovery of large negative excursions of δ^(13)C in organic matter (down to −55‰) from quartzose sandstones (of the Marquette Range and the Huronian Supergroups, North America) intermediate in age between the last Paleoproterozoic glaciation and the possible onset of the Lomagundi event. The negative excursion is concomitant with the appearance of intensely weathered quartzose sandstones, which may represent hot and humid conditions. There are some interpretations that potentially explain the negative excursions: (1) redeposition of older ^(13)C-depleted kerogen, (2) later post-depositional infiltration of oil, (3) active methane productions by methanogens in shallow-marine environments, or (4) dissociation of methane hydrate. If the latter two were the case, they would provide clues for understanding the environmental change connecting the intense glaciation and an increase in oxygen
D-brane Charges in Gravitational Duals of 2+1 Dimensional Gauge Theories and Duality Cascades
We perform a systematic analysis of the D-brane charges associated with
string theory realizations of d=3 gauge theories, focusing on the examples of
the N=4 supersymmetric U(N)xU(N+M) Yang-Mills theory and the N=3 supersymmetric
U(N)xU(N+M) Yang-Mills-Chern-Simons theory. We use both the brane construction
of these theories and their dual string theory backgrounds in the supergravity
approximation. In the N=4 case we generalize the previously known gravitational
duals to arbitrary values of the gauge couplings, and present a precise mapping
between the gravity and field theory parameters. In the N=3 case, which (for
some values of N and M) flows to an N=6 supersymmetric Chern-Simons-matter
theory in the IR, we argue that the careful analysis of the charges leads to a
shift in the value of the B-field in the IR solution by 1/2, in units where its
periodicity is one, compared to previous claims. We also suggest that the N=3
theories may exhibit, for some values of N and M, duality cascades similar to
those of the Klebanov-Strassler theory.Comment: 47 pages, 9 figures; minor changes, references adde
Branes and fluxes in special holonomy manifolds and cascading field theories
We conduct a study of holographic RG flows whose UV is a theory in 2+1
dimensions decoupled from gravity, and the IR is the N=6,8 superconformal fixed
point of ABJM. The solutions we consider are constructed by warping the
M-theory background whose eight spatial dimensions are manifolds of special
holonomies sp(1) times sp(1) and spin(7). Our main example for the spin(7)
holonomy manifold is the A8 geometry originally constructed by Cvetic, Gibbons,
Lu, and Pope. On the gravity side, our constructions generalize the earlier
construction of RG flow where the UV was N=3 Yang-Mills-Chern-Simons matter
system and are simpler in a number of ways. Through careful consideration of
Page, Maxwell, and brane charges, we identify the discrete and continuous
parameters characterizing each system. We then determine the range of the
discrete data, corresponding to the flux/rank for which the supersymmetry is
unbroken, and estimate the dynamical supersymmetry breaking scale as a function
of these data. We then point out the similarity between the physics of
supersymmetry breaking between our system and the system considered by
Maldacena and Nastase. We also describe the condition for unbroken
supersymmetry on class of construction based on a different class of spin(7)
manifolds known as B8 spaces whose IR is different from that of ABJM and
exhibit some interesting features.Comment: 51 pages, 12 figures. Update in quantization of G4 on B8 in equations
(5.12) and (5.13
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