12 research outputs found
Fluctuations along supersymmetric flat directions during Inflation
We consider a set of scalar fields, consisting of a single flat direction and
one or several non-flat directions. We take our cue from the MSSM, considering
separately D-flat and F-flat directions, but our results apply to any
supersymmetric scenario containing flat directions. We study the field
fluctuations during pure de Sitter Inflation, following the evolution of the
infrared modes by numerically solving the appropriate Langevin equations. We
demonstrate that for the Standard Model U(1), SU(2) or SU(3) gauge couplings,
as well as for large enough Yukawa couplings, the fluctuations along the
non-flat directions effectively block the fluctuations along the flat
directions. The usual expected behaviour \propto N, with N the
number of efolds, may be strongly violated, depending on the coupling
strengths. As a consequence, those cosmological considerations, which are
derived assuming that during inflation flat directions fluctuate freely, should
be revised.Comment: 19 pages, 5 figures, Submitted to JCA
Gauge-invariant perturbations at second order in two-field inflation
We study the second-order gauge-invariant adiabatic and isocurvature
perturbations in terms of the scalar fields present during inflation, along
with the related fully non-linear space gradient of these quantities. We
discuss the relation with other perturbation quantities defined in the
literature. We also construct the exact cubic action of the second-order
perturbations (beyond any slow-roll or super-horizon approximations and
including tensor perturbations), both in the uniform energy density gauge and
the flat gauge in order to settle various gauge-related issues. We thus provide
the tool to calculate the exact non-Gaussianity beyond slow-roll and at any
scale.Comment: 28 pages, no figures. v2: Added a summary subsection 4.3 with further
discussion of the results. Generalized all super-horizon results of section 4
and appendix A to exact ones. Other minor textual changes and references
added. Conclusions unchanged. Matches published versio
Multiple field inflation
Inflation offers a simple model for very early evolution of our Universe and
the origin of primordial perturbations on large scales. Over the last 25 years
we have become familiar with the predictions of single-field models, but
inflation with more than one light scalar field can alter preconceptions about
the inflationary dynamics and our predictions for the primordial perturbations.
I will discuss how future observational data could distinguish between
inflation driven by one field, or many fields. As an example, I briefly review
the curvaton as an alternative to the inflaton scenario for the origin of
structure.Comment: 27 pages, no figures. To appear in proceedings of 22nd IAP
Colloquium, Inflation +25, Paris, June 200
Nonlinear superhorizon perturbations of non-canonical scalar field
We develop a theory of non-linear cosmological perturbations at superhorizon
scales for a scalar field with a Lagrangian of the form , where
and is the scalar field. We
employ the ADM formalism and the spatial gradient expansion approach to obtain
general solutions valid up to the second order in the gradient expansion. This
formulation can be applied to, for example, DBI inflation models to investigate
superhorizon evolution of non-Gaussianities. With slight modification, we also
obtain general solutions valid up to the same order for a perfect fluid with a
general equation of state .Comment: 14 page
Inflationary perturbation theory is geometrical optics in phase space
A pressing problem in comparing inflationary models with observation is the
accurate calculation of correlation functions. One approach is to evolve them
using ordinary differential equations ("transport equations"), analogous to the
Schwinger-Dyson hierarchy of in-out quantum field theory. We extend this
approach to the complete set of momentum space correlation functions. A formal
solution can be obtained using raytracing techniques adapted from geometrical
optics. We reformulate inflationary perturbation theory in this language, and
show that raytracing reproduces the familiar "delta N" Taylor expansion. Our
method produces ordinary differential equations which allow the Taylor
coefficients to be computed efficiently. We use raytracing methods to express
the gauge transformation between field fluctuations and the curvature
perturbation, zeta, in geometrical terms. Using these results we give a compact
expression for the nonlinear gauge-transform part of fNL in terms of the
principal curvatures of uniform energy-density hypersurfaces in field space.Comment: 22 pages, plus bibliography and appendix. v2: minor changes, matches
version published in JCA
A parton picture of de Sitter space during slow-roll inflation
It is well-known that expectation values in de Sitter space are afflicted by
infra-red divergences. Long ago, Starobinsky proposed that infra-red effects in
de Sitter space could be accommodated by evolving the long-wavelength part of
the field according to the classical field equations plus a stochastic source
term. I argue that--when quantum-mechanical loop corrections are taken into
account--the separate-universe picture of superhorizon evolution in de Sitter
space is equivalent, in a certain leading-logarithm approximation, to
Starobinsky's stochastic approach. In particular, the time evolution of a box
of de Sitter space can be understood in exact analogy with the DGLAP evolution
of partons within a hadron, which describes a slow logarithmic evolution in the
distribution of the hadron's constituent partons with the energy scale at which
they are probed.Comment: 36 pages; uses iopart.cls and feynmp.sty. v2: Minor typos corrected.
Matches version published in JCA
Enhancement of Non-Gaussianity after Inflation
We study the evolution of cosmological perturbations on large scales, up to
second order, for a perfect fluid with generic equation of state. Taking
advantage of super-horizon conservation laws, it is possible to follow the
evolution of the non-Gaussianity of perturbations through the different stages
after inflation. We find that a large non-linearity is generated by the
gravitational dynamics from the original inflationary quantum fluctuations.
This leads to a significant enhancement of the tiny intrinsic non-Gaussianity
produced during inflation in single-field slow-roll models.Comment: 12 pages, LaTeX file. Revised to match the final version accepted for
publication on JHE
Lectures on inflation and cosmological perturbations
The purpose of these lectures is to give a pedagogical introduction to
inflation and the production of primordial perturbations, as well as a review
of some of the latest developments in this domain. After a short introduction,
we review the main principles of the Hot Big Bang model, as well as its
limitations. This motivates the study of cosmological inflation induced by a
slow-rolling scalar field. We then turn to the analysis of cosmological
perturbations, and explain how the vacuum quantum fluctuations are amplified
during an inflationary phase. The next step consists in relating the
perturbations generated during inflation to the perturbations of the
cosmological fluid in the radiation dominated phase. The final part of these
lectures gives a review of more general models of inflation, involving multiple
fields or non standard kinetic terms. Although more complicated, these models
are usually motivated by high energy physics and they can lead to specific
signatures that are not expected in the simplest models of inflation. After
introducing a very general formalism to describe perturbations in multi-field
models with arbitrary kinetic terms, several interesting cases are presented.
We also stress the role of entropy perturbations in the context of multi-field
models. Finally, we discuss in detail the non-Gaussianities of the primordial
perturbations and some models that could produce a detectable level of
non-Gaussianities.Comment: 56 pages, 5 figures; Lectures given at the Second TRR33 Winter School
on cosmology, Passo del Tonale (Italy), December 200
The Effect of Atopy in the Prevalence of Contact Sensitization: The Experience of a Greek Referral Center
Contact dermatitis is a well-known skin condition, which is related to stimuli and environmental exposure to chemicals, affecting all ages as well as both genders. In the present work, we attempt to investigate the patterns of contact sensitization, with respect to the personal history of atopy (AT), in Greece in a large number of allergens, using patch testing. The retrospective analysis included clinical routine data of 1978 patients collected from 2014 to 2016 in the Laboratory of Patch Testing, National Referral Centre of Occupational Dermatoses. Sensitization, in all cases, was tested with 28 allergens of the European baseline series as adjusted to our local circumstances and clinical experience. A total population of 1978 patients was evaluated, with a male-to-female ratio of 0.45 (1359 females/619 males). From our patient cohort, 693 (35%) patients were evaluated with a history of atopy, while 1285 (65%) were nonatopic. The five most prevalent allergens in the total population without AT were nickel sulphate 5% (15.47%), fragrance mix (I) 8% (9.10%), balsam of Peru (6.47%), cobalt chloride 1% (4.70%), and thiomersal 0.1% (4.10%). Respectively, in the total population with AT, the five most prevalent allergens were nickel sulphate 5% (10.36%), fragrance mix (I) 8% (5.11%), balsam of Peru (3.29%), thiomersal 0.1% (3.03%), and cobalt chloride 1% (2.78%). Contact dermatitis surveillance is of great importance towards the clinical and systematic understanding of the disease. Further studies should be directed towards that end, in order to facilitate more effective health policies. © 2020 Anna Tagka et al
Urticaria from the Neurodermatological Perspective: A Temporal Analysis of Urticaria and Cognition
Chronic spontaneous urticaria (CSU, or CU) is a disease that significantly affects the quality of life of patients. The connection between the cognitive state of an individual and dermatological diseases has been previously reported, and it is known, although not thoroughly investigated, that there is a cognitive and quality of life relation to dermal pathologies. Urticaria is a chronic disease that requires a specialized approach to diagnosis and treatment but also a holistic approach with respect to the consideration of both the pathophysiology of the disease and the cognition status of the patient. The present study aims at analyzing CU score and cognitive indexes with respect to time, as a time series and their subsequent interactions. We have attempted to model the investigated time series in order to unravel possible causative relationships between cognitive/quality of life factors and urticaria. One hundred and eleven patients (29 males/82 females) admitted to our department were diagnosed with CU. CU was estimated on UAS7 score basis, which was used in order to define disease severity. Indexes used for assessing the cognitive and quality of life of patients’ status included the Urticaria Control Test (UCT) and Dermatology Life Quality Index (DLQI). Significant correlations were found between UAS7 score and the UCT and DLQI scores, respectively. Interestingly, each score time series was modelled by different sets of equations, indicating the unique effect each one has on the disease, as well as that each score probably is manifested by a different pathophysiological mechanism. © 2021, The Author(s), under exclusive license to Springer Nature Switzerland AG