136 research outputs found
Cosmic Microwave Background Statistics for a Direction-Dependent Primordial Power Spectrum
Statistical isotropy of primordial perturbations is a common assumption in
cosmology, but it is an assumption that should be tested. To this end, we
develop cosmic microwave background statistics for a primordial power spectrum
that depends on the direction, as well as the magnitude, of the Fourier
wavevector. We first consider a simple estimator that searches in a
model-independent way for anisotropy in the square of the temperature (and/or
polarization) fluctuation. We then construct the minimum-variance estimators
for the coefficients of a spherical-harmonic expansion of the
direction-dependence of the primordial power spectrum. To illustrate, we apply
these statistics to an inflation model with a quadrupole dependence of the
primordial power spectrum on direction and find that a power quadrupole as
small as 2.0% can be detected with the Planck satellite.Comment: Published in Phys. Rev. D; 8 pages; 1 table; Table 1 corrected;
references adde
Testable polarization predictions for models of CMB isotropy anomalies
Anomalies in the large-scale CMB temperature sky measured by WMAP have been
suggested as possible evidence for a violation of statistical isotropy on large
scales. In any physical model for broken isotropy, there are testable
consequences for the CMB polarization field. We develop simulation tools for
predicting the polarization field in models that break statistical isotropy
locally through a modulation field. We study two different models: dipolar
modulation, invoked to explain the asymmetry in power between northern and
southern ecliptic hemispheres, and quadrupolar modulation, posited to explain
the alignments between the quadrupole and octopole. For the dipolar case, we
show that predictions for the correlation between the first 10 multipoles of
the temperature and polarization fields can typically be tested at better than
the 98% CL. For the quadrupolar case, we show that the polarization quadrupole
and octopole should be moderately aligned. Such an alignment is a generic
prediction of explanations which involve the temperature field at recombination
and thus discriminate against explanations involving foregrounds or local
secondary anisotropy. Predicted correlations between temperature and
polarization multipoles out to l = 5 provide tests at the ~ 99% CL or stronger
for quadrupolar models that make the temperature alignment more than a few
percent likely. As predictions of anomaly models, polarization statistics move
beyond the a posteriori inferences that currently dominate the field.Comment: 17 pages, 15 figures; published in PRD; references adde
Non-Linear Relativity in Position Space
We propose two methods for obtaining the dual of non-linear relativity as
previously formulated in momentum space. In the first we allow for the (dual)
position space to acquire a non-linear representation of the Lorentz group
independently of the chosen representation in momentum space. This requires a
non-linear definition for the invariant contraction between momentum and
position spaces. The second approach, instead, respects the linearity of the
invariant contraction. This fully fixes the dual of momentum space and dictates
a set of energy-dependent space-time Lorentz transformations. We discuss a
variety of physical implications that would distinguish these two strategies.
We also show how they point to two rather distinct formulations of theories of
gravity with an invariant energy and/or length scale.Comment: 7 pages, revised versio
Operational indistinguishably of varying speed of light theories
The varying speed of light theories have been recently proposed to solve the
standard model problems and anomalies in the ultra high energy cosmic rays.
These theories try to formulate a new relativity with no assumptions about the
constancy of the light speed. In this regard, we study two theories and want to
show that these theories are not the new theories of relativity, but only
re-descriptions of Einstein's special relativity.Comment: 5 pages, 2 figures, title changed, minor changes in notations and
formulae, a paragraph added, Int. J. Mod. Phys. D (in press) v
Speed of light in the extended gravity theories
We shall investigate the possibility of formulation of varying speed of light
(VSL) in the framework of Palatini non-linear Ricci scalar and Ricci squared
theories. Different speeds of light including the causal structure constant,
electromagnetic, and gravitational wave speeds are discussed. We shall see that
two local frames are distinguishable and discuss about the velocity of light in
these two frames. We shall investigate which one of these local frames is
inertial.Comment: 19 pages. to appear in Classical Quantum Gravit
Anomalous CMB polarization and gravitational chirality
We consider the possibility that gravity breaks parity, with left and right
handed gravitons coupling to matter with a different Newton's constant and show
that this would affect their zero-point vacuum fluctuations during inflation.
Should there be a cosmic background of gravity waves, the effect would
translate into anomalous CMB polarization. Non-vanishing TB (and EB)
polarization components emerge, revealing interesting experimental targets.
Indeed if reasonable chirality is present a TB measurement would provide the
easiest way to detect a gravitational wave background. We speculate on the
theoretical implications of such an observation.Comment: 5 pages, 1 figur
Lorentz invariance with an invariant energy scale
We propose a modification of special relativity in which a physical energy,
which may be the Planck energy, joins the speed of light as an invariant, in
spite of a complete relativity of inertial frames and agreement with Einstein's
theory at low energies. This is accomplished by a non-linear modification of
the action of the Lorentz group on momentum space, generated by adding a
dilatation to each boost in such a way that the Planck energy remains
invariant. The associated algebra has unmodified structure constants, and we
highlight the similarities between the group action found and a transformation
previously proposed by Fock. We also discuss the resulting modifications of
field theory and suggest a modification of the equivalence principle which
determines how the new theory is embedded in general relativity
Non-Gaussian signatures of Tachyacoustic Cosmology
I investigate non-Gaussian signatures in the context of tachyacoustic
cosmology, that is, a noninflationary model with superluminal speed of sound. I
calculate the full non-Gaussian amplitude , its size ,
and corresponding shapes for a red-tilted spectrum of primordial scalar
perturbations. Specifically, for cuscuton-like models I show that , and the shape of its non-Gaussian amplitude peaks for
both equilateral and local configurations, the latter being dominant. These
results, albeit similar, are quantitatively distinct from the corresponding
ones obtained by Magueijo {\it{et. al}} in the context of superluminal bimetric
models.Comment: Some comments and references added. Matches the version published in
JCA
Storming Majorana's Tower with OAM states of light in a plasma
We extend the relationship between mass and spin angular momentum, described
by the bosonic spectrum of positive definite mass particles of the Majorana
solution to the Dirac equation, to photons that acquire an effective Proca mass
through the Anderson-Higgs mechanism when they propagate in a plasma. In an
earlier paper we showed that if the plasma is structured, it can impart orbital
angular momentum (OAM) to the photons that reduces the total Proca photon mass.
Here we show, through a generalisation of Majorana's solution, that photons
with OAM in a plasma cannot assume negative squared mass states. This means
that there exist interesting analogies with Quantum Gravity or General
Relativity models involving a modified action of the Lorentz group.Comment: 4 pages; Corrected, updated versio
The Mystery of Alpha and the Isotopes
We report unbiased AI measurements of the fine structure constant alpha in
two proximate absorption regions in the spectrum of the quasar HE0515-4414. The
data are high resolution, high signal to noise, and laser frequency comb
calibrated, obtained using the ESPRESSO spectrograph on the VLT. The high
quality of the data and proximity of the regions motivate a differential
comparison, exploring the possibility of spatial variations of fundamental
constants, as predicted in some theories. We show that if the magnesium
isotopic relative abundances are terrestrial, the fine structure constants in
these two systems differ at the 7-sigma level. A 3-sigma discrepancy between
the two measurements persists even for the extreme non-terrestrial case of 100%
^{24}Mg, if shared by both systems. However, if Mg isotopic abundances take
independent values in these two proximate systems, one terrestrial, the other
with no heavy isotopes, both can be reconciled with a terrestrial alpha, and
the discrepancy between the two measurements falls to 2-sigma. We discuss
varying constant and varying isotope interpretations and resolutions to this
conundrum for future high precision measurements.Comment: 6 pages, 3 figure
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