324 research outputs found
Parity violation in the Cosmic Microwave Background from a pseudoscalar inflaton
If the inflaton is a pseudoscalar, then it naturally interacts with gauge
fields via an axion-like coupling to . Through
this coupling, the rolling inflaton produces quanta of the gauge field, that in
their turn source the tensor components of the metric perturbations. Due to the
parity-violating nature of the system, the right- and the left-handed tensor
modes have different amplitudes. Such an asymmetry manifests itself in the form
of non-vanishing TB and EB correlation functions in the Cosmic Microwave
Background (CMB). We compute the amplitude of the parity-violating tensor modes
and we discuss two scenarios, consistent with the current data, where
parity-violating CMB correlation functions will be detectable in future
experiments.Comment: 9 pages, 1 figure; v2: a minor numerical mistake corrected,
references added; v3: minor changes, matches published versio
The interrelation between the generation of large-scale electric fields and that of large-scale magnetic fields during inflation
The interrelation between the generation of large-scale electric fields and
that of large-scale magnetic fields due to the breaking of the conformal
invariance of the electromagnetic field in inflationary cosmology is studied.
It is shown that if large-scale magnetic fields with a sufficiently large
amplitude are generated during inflation, the generation of large-scale
electric fields is suppressed, and vice versa. Furthermore, a physical
interpretation of the result and its cosmological significance are considered.Comment: 12 pages, no figure, title changed, typos correcte
Continuity, Deconfinement, and (Super) Yang-Mills Theory
We study the phase diagram of SU(2) Yang-Mills theory with one adjoint Weyl
fermion on R^3xS^1 as a function of the fermion mass m and the compactification
scale L. This theory reduces to thermal pure gauge theory as m->infinity and to
circle-compactified (non-thermal) supersymmetric gluodynamics in the limit
m->0. In the m-L plane, there is a line of center symmetry changing phase
transitions. In the limit m->infinity, this transition takes place at
L_c=1/T_c, where T_c is the critical temperature of the deconfinement
transition in pure Yang-Mills theory. We show that near m=0, the critical
compactification scale L_c can be computed using semi-classical methods and
that the transition is of second order. This suggests that the deconfining
phase transition in pure Yang-Mills theory is continuously connected to a
transition that can be studied at weak coupling. The center symmetry changing
phase transition arises from the competition of perturbative contributions and
monopole-instantons that destabilize the center, and topological molecules
(neutral bions) that stabilize the center. The contribution of molecules can be
computed using supersymmetry in the limit m=0, and via the
Bogomolnyi--Zinn-Justin (BZJ) prescription in the non-supersymmetric gauge
theory. Finally, we also give a detailed discussion of an issue that has not
received proper attention in the context of N=1 theories---the non-cancellation
of nonzero-mode determinants around supersymmetric BPS and KK
monopole-instanton backgrounds on R^3xS^1. We explain why the non-cancellation
is required for consistency with holomorphy and supersymmetry and perform an
explicit calculation of the one-loop determinant ratio.Comment: A discussion of the non-cancellation of the nonzero mode determinants
around supersymmetric monopole-instantons in N=1 SYM on R^3xS^1 is added,
including an explicit calculation. The non-cancellation is, in fact, required
by supersymmetry and holomorphy in order for the affine-Toda superpotential
to be reproduced. References have also been adde
Phenomenology of a Pseudo-Scalar Inflaton: Naturally Large Nongaussianity
Many controlled realizations of chaotic inflation employ pseudo-scalar
axions. Pseudo-scalars \phi are naturally coupled to gauge fields through c
\phi F \tilde{F}. In the presence of this coupling, gauge field quanta are
copiously produced by the rolling inflaton. The produced gauge quanta, in turn,
source inflaton fluctuations via inverse decay. These new cosmological
perturbations add incoherently with the "vacuum" perturbations, and are highly
nongaussian. This provides a natural mechanism to generate large nongaussianity
in single or multi field slow-roll inflation. The resulting phenomenological
signatures are highly distinctive: large nongaussianity of (nearly) equilateral
shape, in addition to detectably large values of both the scalar spectral tilt
and tensor-to-scalar ratio (both being typical of large field inflation). The
WMAP bound on nongaussianity implies that the coupling, c, of the pseudo-scalar
inflaton to any gauge field must be smaller than about 10^{2} M_p^{-1}.Comment: 45 pages, 7 figure
A new cubic theory of gravity in five dimensions: Black hole, Birkhoff's theorem and C-function
We present a new cubic theory of gravity in five dimensions which has second
order traced field equations, analogous to BHT new massive gravity in three
dimensions. Moreover, for static spherically symmetric spacetimes all the field
equations are of second order, and the theory admits a new asymptotically
locally flat black hole. Furthermore, we prove the uniqueness of this solution,
study its thermodynamical properties, and show the existence of a C-function
for the theory following the arguments of Anber and Kastor (arXiv:0802.1290
[hep-th]) in pure Lovelock theories. Finally, we include the
Einstein-Gauss-Bonnet and cosmological terms and we find new asymptotically AdS
black holes at the point where the three maximally symmetric solutions of the
theory coincide. These black holes may also possess a Cauchy horizon.Comment: 21 pages, no figures, V2: two appendices and some references added,
V3: New section on the generalization to arbitrary higher order. Analogy with
BHT new massive gravity Lagrangian made more precise, V4: Typos corrected. To
appear in CQ
Large-scale magnetic fields from inflation due to Chern-Simons-like effective interaction
We discuss the generation of large-scale magnetic fields due to the breaking
of the conformal invariance in the electromagnetic field through the -even
dimension-six Chern-Simons-like effective interaction with a fermion current in
inflationary cosmology. It is shown that the magnetic fields on 1Mpc scale with
the field strength of G at the present time can be generated even
for the scale of the effective interaction being the Planck scale.Comment: 13 pages, 2 figures, additional explanations include
Non-Gaussianities in N-flation
We compute non-Gaussianities in N-flation, a string motivated model of
assisted inflation with quadratic, separable potentials and masses given by the
Marcenko-Pastur distribution. After estimating parameters characterizing the
bi- and trispectrum in the horizon crossing approximation, we focus on the
non-linearity parameter , a measure of the bispectrum; we compute its
magnitude for narrow and broad spreads of masses, including the evolution of
modes after horizon crossing. We identify additional contributions due to said
evolution and show that they are suppressed as long as the fields are evolving
slowly. This renders -flation indistinguishable from simple
single-field models in this regime. Larger non-Gaussianities are expected to
arise for fields that start to evolve faster, and we suggest an analytic
technique to estimate their contribution. However, such fast roll during
inflation is not expected in N-flation, leaving (p)re-heating as the main
additional candidate for generating non-Gaussianities.Comment: 27 pages, 4 figures, extended references to match version accepted in
JCA
Beta functions of topologically massive supergravity
We compute the one-loop beta functions of the cosmological constant, Newton's constant and the topological mass in topologically massive supergravity in three dimensions. We use a variant of the proper time method supplemented by a simple choice of cutoff function. We also employ two different analytic continuations of AdS3 and consider harmonic expansions on the 3-sphere as well as a 3-hyperboloid, and then show that they give the same results for the beta functions. We find that the dimensionless coefficient of the Chern-Simons term, 28, has vanishing beta function. The flow of the cosmological constant and Newton's constant depends on 28; we study analytically the structure of the flow and its fixed points in the limits of small and large ?. Open Access, \ua9 2014 The Authors
Seiberg-Witten and "Polyakov-like" magnetic bion confinements are continuously connected
We study four-dimensional N=2 supersymmetric pure-gauge (Seiberg-Witten)
theory and its N=1 mass perturbation by using compactification S**1 x R**3. It
is well known that on R**4 (or at large S**1) the perturbed theory realizes
confinement through monopole or dyon condensation. At small S**1, we
demonstrate that confinement is induced by a generalization of Polyakov's
three-dimensional instanton mechanism to a locally four-dimensional theory -
the magnetic bion mechanism - which also applies to a large class of
nonsupersymmetric theories. Using a large- vs. small-L Poisson duality, we show
that the two mechanisms of confinement, previously thought to be distinct, are
in fact continuously connected.Comment: 49 pages, 5 figure
The semi-classical expansion and resurgence in gauge theories: new perturbative, instanton, bion, and renormalon effects
We study the dynamics of four dimensional gauge theories with adjoint
fermions for all gauge groups, both in perturbation theory and
non-perturbatively, by using circle compactification with periodic boundary
conditions for the fermions. There are new gauge phenomena. We show that, to
all orders in perturbation theory, many gauge groups are Higgsed by the gauge
holonomy around the circle to a product of both abelian and nonabelian gauge
group factors. Non-perturbatively there are monopole-instantons with fermion
zero modes and two types of monopole-anti-monopole molecules, called bions. One
type are "magnetic bions" which carry net magnetic charge and induce a mass gap
for gauge fluctuations. Another type are "neutral bions" which are magnetically
neutral, and their understanding requires a generalization of multi-instanton
techniques in quantum mechanics - which we refer to as the
Bogomolny-Zinn-Justin (BZJ) prescription - to compactified field theory. The
BZJ prescription applied to bion-anti-bion topological molecules predicts a
singularity on the positive real axis of the Borel plane (i.e., a divergence
from summing large orders in peturbation theory) which is of order N times
closer to the origin than the leading 4-d BPST instanton-anti-instanton
singularity, where N is the rank of the gauge group. The position of the
bion--anti-bion singularity is thus qualitatively similar to that of the 4-d IR
renormalon singularity, and we conjecture that they are continuously related as
the compactification radius is changed. By making use of transseries and
Ecalle's resurgence theory we argue that a non-perturbative continuum
definition of a class of field theories which admit semi-classical expansions
may be possible.Comment: 112 pages, 7 figures; v2: typos corrected, discussion of
supersymmetric models added at the end of section 8.1, reference adde
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