134 research outputs found
Magnetic field evolution in giant radio relics using the example of CIZA J2242.8+5301
Article / Letter to editorSterrewach
Magnetic field evolution in giant radio relics using the example of CIZA J2242.8+5301
Large scale structure and cosmolog
Inflation with General Initial Conditions for Scalar Perturbations
We explore the possibility of a single field quasi-de Sitter inflationary
model with general initial state for primordial fluctuations. In this paper,
first we compute the power spectrum and the bispectrum of scalar perturbations
with coherent state as the initial state. We find that a large class of
coherent states are indistinguishable from the Bunch-Davies vacuum state and
hence consistent with the current observations. In case of a more general
initial state built over Bunch-Davies vacuum state, we show that the
constraints on the initial state from observed power spectrum and local
bispectrum are relatively weak and for quasi-de Sitter inflation a large number
of initial states are consistent with the current observations. However,
renormalizability of the energy-momentum tensor of the fluctuations constraints
the initial state further.Comment: Updated to match published version, 20 page
Group theoretical approach to quantum fields in de Sitter space I. The principal series
Using unitary irreducible representations of the de Sitter group, we
construct the Fock space of a massive free scalar field.
In this approach, the vacuum is the unique dS invariant state. The quantum
field is a posteriori defined by an operator subject to covariant
transformations under the dS isometry group. This insures that it obeys
canonical commutation relations, up to an overall factor which should not
vanish as it fixes the value of hbar. However, contrary to what is obtained for
the Poincare group, the covariance condition leaves an arbitrariness in the
definition of the field. This arbitrariness allows to recover the amplitudes
governing spontaneous pair creation processes, as well as the class of alpha
vacua obtained in the usual field theoretical approach. The two approaches can
be formally related by introducing a squeezing operator which acts on the state
in the field theoretical description and on the operator in the present
treatment. The choice of the different dS invariant schemes (different alpha
vacua) is here posed in very simple terms: it is related to a first order
differential equation which is singular on the horizon and whose general
solution is therefore characterized by the amplitude on either side of the
horizon. Our algebraic approach offers a new method to define quantum field
theory on some deformations of dS space.Comment: 35 pages, 2 figures ; Corrected typo, Changed referenc
Jorge A. Swieca's contributions to quantum field theory in the 60s and 70s and their relevance in present research
After revisiting some high points of particle physics and QFT of the two
decades from 1960 to 1980, I comment on the work by Jorge Andre Swieca. I
explain how it fits into the quantum field theory during these two decades and
draw attention to its relevance to the ongoing particle physics research. A
particular aim of this article is to direct thr readers mindfulness to the
relevance of what at the time of Swieca was called "the Schwinger Higgs
screening mechanism". which, together with recent ideas which generalize the
concept of gauge theories, has all the ingredients to revolutionize the issue
of gauge theories and the standard model.Comment: 49 pages, expansion and actualization of text, improvement of
formulations and addition of many references to be published in EPJH -
Historical Perspectives on Contemporary Physic
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