166 research outputs found
Gelfand-Dikii Brackets for Nonstandard Supersymmetric Systems
We show how a general nonstandard Lax equation (supersymmetric or otherwise)
can be expressed as a standard Lax equation. This enables us to define the
Gelfand-Dikii brackets for a nonstandard supersymmetric equation. We discuss
the Hamiltonian structures for the nonstandard super KP system and work out
explicitly the two Hamiltonian structures of the supersymmetric Two Boson
system from this point of view.Comment: Plain Tex file, no figure
Cosmological spectrum of two-point correlation function from vacuum fluctuation of Stringy Axion field in De Sitter space: A study of the role of Quantum Entanglement
In this work, we study the impact of quantum entanglement on the two-point
correlation function and the associated primordial power spectrum of mean
square vacuum fluctuation in a bipartite quantum field theoretic system. The
field theory that we consider is the effective theory of axion field arising
from Type IIB string theory compactified to four dimensions. We compute the
expression for the power spectrum of vacuum fluctuation in three different
approaches, namely (1) field operator expansion (FOE) technique with the
quantum entangled state, (2) reduced density matrix (RDM) formalism with mixed
quantum state and (3) the method of non-entangled state (NES). For massless
axion field, in all these three formalism, we reproduce, at the leading order,
the exact scale-invariant power spectrum which is well known in the literature.
We observe that due to quantum entanglement, the sub-leading terms for these
thee formalisms are different. Thus, such correction terms break the degeneracy
among the analysis of the FOE, RDM and NES formalisms in the super-horizon
limit. On the other hand, for massive axion field, we get a slight deviation
from scale invariance and exactly quantify the spectral tilt of the power
spectrum in small scales. Apart from that, for massless and massive axion
field, we find distinguishable features of the power spectrum for the FOE, RDM,
and NES on the large scales, which is the result of quantum entanglement. We
also find that such large-scale effects are comparable to or greater than the
curvature radius of the de Sitter space. Most importantly, in the near future,
if experiments probe for early universe phenomena, one can detect such small
quantum effects. In such a scenario, it is possible to test the implications of
quantum entanglement in primordial cosmology.Comment: 75 pages, 13 figures, 1 table, Revised version, This work published
is published in Universe as part of the Special Issue "Cosmic String Theory
and Observations
COSMOS--GTachyon from String Theory
In this article, our prime objective is to study the inflationary paradigm
from generalized tachyon (GTachyon) living on the world volume of a non-BPS
string theory. The tachyon action is considered here is getting modified
compared to the original action. One can quantify the amount of the
modification via a power instead of in the effective action. Using
this set up we study inflation from various types of tachyonic potentials,
using which we constrain the index within, , Regge slope
, string coupling constant and mass scale of tachyon ,
from the recent Planck 2015 and Planck+BICEP2/Keck Array joint data. We
explicitly study the inflationary consequences from single field, assisted
field and multi-field tachyon set up. Specifically for single field and
assisted field case we derive the results in the quasi-de-Sitter background in
which we will utilize the details of cosmological perturbations and quantum
fluctuations. Also we derive the expressions for all inflationary observables
using any arbitrary vacuum and Bunch-Davies vacuum. For single field and
assisted field case we derive-the inflationary flow equations, new sets of
consistency relations. Also we derive the field excursion formula for tachyon,
which shows that assisted inflation is in more safer side compared to the
single field case to validate effective field theory framework. Further we
study the features of CMB Angular power spectrum from TT, TE and EE
correlations from scalar fluctuations within the allowed range of for each
potentials from single field set-up. We also put constraints from the
temperature anisotropy and polarization spectra, which shows that our analysis
is consistent with the Planck 2015 data. Finally, using formalism we
derive the expressions for inflationary observables in the context of
multi-field tachyons.Comment: 206 pages, 26 figures, 1 table, Final version, Accepted for
publication in European Physical Journal
Quantum entanglement in de Sitter space from Stringy Axion: An analysis using vacua
In this work, we study the phenomena of quantum entanglement by computing de
Sitter entanglement entropy from von Neumann measure. For this purpose we
consider a bipartite quantum field theoretic setup in presence of axion
originating from string theory. We consider the initial
vacuum to be CPT invariant non-adiabatic vacua state under ismometry, which is characterized by a real one-parameter family. To
implement this technique we use a which divide the de Sitter into
two exterior and interior sub-regions. First, we derive the wave function of
axion in an open chart for vacua by applying Bogoliubov transformation
on the solution for Bunch-Davies vacuum state. Further, we quantify the density
matrix by tracing over the contribution from the exterior region. Using this
result we derive entanglement entropy, Rnyi entropy and explain the
long-range quantum effects in primordial cosmological correlations. We also
provide a comparison between the results obtained from Bunch-Davies vacuum and
the generalized vacua, which implies that the amount of quantum
entanglement and the long-range effects are larger for non zero value of the
parameter . Most significantly, our derived results for vacua
provides the necessary condition for generating non zero entanglement entropy
in primordial cosmology.Comment: 31 pages, 13 figures, Revised version, Accepted for publication in
Nuclear Physics
Bounds on Tensor wave and Twisted Inflation
We study the bounds on tensor wave in a class of twisted inflation models
where -branes are wrapped on cycles in the compact manifold and wrap
the KK-direction in the corresponding effective field theory. While the lower
bound is found to be analogous to that in Type IIB models of brane inflation,
the upper bound turns out to be significantly different. This is argued for a
range of values for the parameter satisfying the self-consistency
relation and the WMAP data. Further, we observe that the wrapped -brane
appears to be the most attractive from a cosmological perspective.Comment: 5 page
Bell violation in the Sky
In this work, we have studied the possibility of setting up Bell's inequality
violating experiment in the context of cosmology, based on the basic principles
of quantum mechanics. First we start with the physical motivation of
implementing the Bell's inequality violation in the context of cosmology. Then
to set up the cosmological Bell violating test experiment we introduce a model
independent theoretical framework using which we have studied the creation of
new massive particles by implementing the WKB approximation method for the
scalar fluctuations in presence of additional time dependent mass contribution.
Next using the background scalar fluctuation in presence of new time dependent
mass contribution, we explicitly compute the expression for the one point and
two point correlation functions. Furthermore, using the results for one point
function we introduce a new theoretical cosmological parameter which can be
expressed in terms of the other known inflationary observables and can also be
treated as a future theoretical probe to break the degeneracy amongst various
models of inflation. Additionally, we also fix the scale of inflation in a
model independent way without any prior knowledge of primordial gravitational
waves. Next, we also comment on the technicalities of measurements from isospin
breaking interactions and the future prospects of newly introduced massive
particles in cosmological Bell violating test experiment. Further, we cite a
precise example of this set up applicable in the context of string theory
motivated axion monodromy model. Then we comment on the explicit role of
decoherence effect and high spin on cosmological Bell violating test
experiment. In fine, we provide a theoretical bound on the heavy particle mass
parameter for scalar fields, graviton and other high spin fields from our
proposed setup.Comment: 202 pages, 16 figures, 1 table, Accepted for publication in European
Physical Journal
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