6,194 research outputs found
The different varieties of the Suyama-Yamaguchi consistency relation and its violation as a signal of statistical inhomogeneity
We present the different consistency relations that can be seen as variations
of the well known Suyama-Yamaguchi (SY) consistency relation \tau_{NL}
\geqslant ((6/5) f_{NL})^2. It has been claimed that the following variation:
\tau_{NL} ({\bf k}_1, {\bf k_3}) \geqslant (6/5)^2 f_{NL} ({\bf k}_1) f_{NL}
({\bf k}_3), which we call "the fourth variety", in the collapsed (for
\tau_{NL}) and squeezed (for f_{NL}) limits is always satisfied independently
of any physics; however, the proof depends sensitively on the assumption of
scale-invariance which only applies for cosmological models involving
Lorentz-invariant scalar fields (at least at tree level), leaving room for a
strong violation of this variety of the consistency relation when non-trivial
degrees of freedom, for instance vector fields, are in charge of the generation
of \zeta. With this in mind as a motivation, we explicitly state under which
conditions the SY consistency relation has been claimed to hold in its
different varieties (implicitly) presented in the literature; as a result, we
show for the first time that the variety \tau_{NL} ({\bf k}_1, {\bf k}_1)
\geqslant ((6/5) f_{NL} ({\bf k}_1))^2, which we call "the fifth variety", is
always satisfied even when there is strong scale-dependence as long as
statistical homogeneity holds: thus, an observed violation of this specific
variety would prevent the comparison between theory and observation, shaking
this way the foundations of cosmology as a science. Later, we concern about the
existence of non-trivial degrees of freedom, concretely vector fields for which
the levels of non-gaussianity have been calculated for very few models, finding
that the fourth variety of the SY consistency relation is indeed strongly
violated for some specific wavevector configurations while the fifth variety
continues to be well satisfied. (Abridged)Comment: LaTex file, 12 pages, 4 figures. v2: minor cosmetic changes,
references added and updated, version to be published in Journal of Cosmology
and Astroparticle Physic
Scale and shape dependent non-Gaussianity in the presence of inflationary vector fields
We consider cosmological inflationary models in which vector fields play some
role in the generation of the primordial curvature perturbation . Such
models are interesting because the involved vector fields naturally seed
statistical anisotropy in the primordial fluctuations which could eventually
leave a measurable imprint on the cosmic microwave background fluctuations. In
this article, we estimate the scale and shape dependent effects on the
non-Gaussianity (NG) parameters due to the scale dependent statistical
anisotropy in the distribution of the fluctuations. For concreteness, we use a
power spectrum (PS) of the fluctuations of the quadrupolar form:
,
where is the only quantity which parametrizes the level of
statistical anisotropy and is a unitary vector which points towards
the preferred direction. Then, we evaluate the contribution of the running of
on the NG parameters by means of the formalism. We
focus specifically on the details for the NG parameter, associated
with the bispectrum , but the structure of higher order NG parameters
is straightforward to generalize. Although the level of statistical anisotropy
in the PS is severely constrained by recent observations, the importance of
statistical anisotropy signals in higher order correlators remains to be
determined, this being the main task that we address here. The precise
measurement of the shape and scale dependence (or running) of statistical
parameters such as the NG parameters and the statistical anisotropy level could
provide relevant elements for model building and for the determination of the
presence (or nonpresence) of inflationary vector fields and their role in the
inflationary mechanism.Comment: LaTex file, 19 pages, 14 figures. v2: the title has been changed a
bit to reflect, in a better way, the purpose and contents of the paper. Just
a few changes to satisfy the referee requirements. Conclusions unchanged.
Version to be published in Physical Review
Feynman-like Rules for Calculating n-Point Correlators of the Primordial Curvature Perturbation
A diagrammatic approach to calculate n-point correlators of the primordial
curvature perturbation \zeta was developed a few years ago following the spirit
of the Feynman rules in Quantum Field Theory. The methodology is very useful
and time-saving, as it is for the case of the Feynman rules in the particle
physics context, but, unfortunately, is not very well known by the cosmology
community. In the present work, we extend such an approach in order to include
not only scalar field perturbations as the generators of \zeta, but also vector
field perturbations. The purpose is twofold: first, we would like the
diagrammatic approach (which we would call the Feynman-like rules) to become
widespread among the cosmology community; second, we intend to give an easy
tool to formulate any correlator of \zeta for those cases that involve vector
field perturbations and that, therefore, may generate prolonged stages of
anisotropic expansion and/or important levels of statistical anisotropy.
Indeed, the usual way of formulating such correlators, using the Wick's
theorem, may become very clutter and time-consuming.Comment: LaTeX file, 26 pages. v2: A short discussion added regarding the role
of the diagrams in high precision cosmology as well as in those cases where
the loop contributions are larger than the tree level terms, generating large
and observable levels of (anisotropic) non-gaussianity; references added,
conclusions unchanged. v3: version to appear in Journal of Cosmology and
Astroparticle Physic
The Suyama-Yamaguchi consistency relation in the presence of vector fields
We consider inflationary models in which vector fields are responsible for
part or eventually all of the primordial curvature perturbation \zeta. Such
models are phenomenologically interesting since they naturally introduce
anisotropies in the probability distribution function of the primordial
fluctuations that can leave a measurable imprint in the cosmic microwave
background. Assuming that non-Gaussianity is generated due to the superhorizon
evolution, we use the \delta N formalism to do a complete tree level
calculation of the non-Gaussianity parameters f_{NL} and \tau_{NL} in the
presence of vector fields. We isolate the isotropic pieces of the
non-Gaussianity parameters, which anyway have contributions from the vector
fields, and show that they obey the Suyama-Yamaguchi consistency relation
\tau^{iso}_{NL}>=(6/5f^{iso}_{NL})^2. Other ways of defining the
non-Gaussianity parameters, which could be observationally relevant, are stated
and the respective Suyama-Yamaguchi-like consistency relations are obtained.Comment: LaTeX file, 11 pages. v2: a few minor changes, references added and
updated. v3: version to be published in Modern Physics Letters
Arbitrarily coupled forms in cosmological backgrounds
In this paper we consider a model based on interacting forms and explore
some cosmological applications. Restricting to gauge invariant actions, we
build a general Lagrangian allowing for arbitrary interactions between the
forms (including interactions with a form, scalar field) in a given
background in dimensions. For simplicity, we restrict the construction to
up to first order derivatives of the fields in the Lagrangian. We discuss with
detail the four dimensional case and devote some attention to the mechanism of
topological mass generation originated by couplings of the form
between a form and a form. As a result, we show the system of the
interacting forms is equivalent to a parity violating, massive,
Proca vector field model. Finally, we discuss some cosmological applications.
In a first case we study a very minimalistic system composed by a form
coupled to a form. The form induces an effective potential which acts
as a cosmological constant term suitable to drive the late time accelerated
expansion of the universe dominated by dark energy. We study the dynamics of
the system and determine its critical points and stability. Additionally, we
study a system composed by a scalar field and a -form. This case is
interesting because the presence of a coupled form can generate non
vanishing anisotropic signatures during the late time accelerated expansion. We
discuss the evolution of cosmological parameters such as the equation of state
in this model.Comment: Several modifications and updates. The discussion about the forms
is reviewed and corrected. A new application included. Several references
added. Main conclusions unchange
de Sitter symmetries and inflationary correlators in parity violating scalar-vector models
In this paper we use conformal field theory techniques to constrain the form
of the correlations functions of an inflationary scalar-vector model described
by the interaction term . We use the fact that the conformal
group is the relevant symmetry group acting on super horizon scales in an
inflationary de Sitter background. As a result, we find that super horizon
conformal symmetry, constraints the form of the coupling functions
to be homogeneous functions of the same degree. We derive the general form of
the correlators involving scalar and vector perturbations in this model and
determine its squeezed limit scaling behaviour for super horizon scales. The
approach followed here is useful to constraint the shape of scalar-vector
correlators, and our results agree with recent literature on the subject, but
don't allow us to determine amplitude factors of the correlators.Comment: References added. Discussion about invariance under special conformal
transformations improved. Matches published versio
Correlation functions of sourced gravitational waves in inflationary scalar vector models. A symmetry based approach
We use conformal symmetry to constrain the shape of inflationary correlators
in the presence of long-lived vector field perturbations. Applying conformal
Ward identities, we derive general expressions, up to amplitudes and
normalization factors, for the two and three point correlators in the presence
of vector fields mediated by the interaction , where is a
suitable coupling function between the scalar and the vector field. The
previous interaction allows for isotropy and parity symmetry breaking and is
consistent with super horizon conformal symmetry. As an application of the
conformal field theory techniques followed here, we evaluate the mixed
tensor-scalar and tensor-scalar-scalar correlators which are interesting to look for
parity violating effects related with chiral gravitational waves. Finally, we
derive consistency relations for the three point correlators obtained.Comment: Typos corrected, some clarifying comments added and references added.
Matches the published versio
An asymmetric jet launching model for the protoplanetary nebula CRL 618
We propose an asymmetrical jet ejection mechanism in order to model the
mirror symmetry observed in the lobe distribution of some protoplanetary
nebulae (pPNe), such as the pPN CRL 618. 3D hydrodynamical simulations of a
precessing jet launched from an orbiting source were carried out including an
alternation in the ejections of the two outflow lobes, depending on which side
of the precessing accretion disk is hit by the accretion column from a Roche
lobe-filling binary companion. Both synthetic optical emission maps and
position-velocity (PV) diagrams were obtained from the numerical results with
the purpose of carrying out a direct comparison with observations. Depending on
the observer's point of view, multipolar morphologies are obtained which
exhibit a mirror symmetry at large distances from the central source. The
obtained lobe sizes and their spatial distribution are in good agreement with
the observed morphology of the pPN CRL 618. We also obtain that the kinematic
ages of the fingers are similar to those obtained in the observations.Comment: 13 pages, 6 figures, submitted to the Astrophysical Journa
Common Underlying Dynamics in an Emerging Market: From Minutes to Months
We analyse a period spanning 35 years of activity in the Sao Paulo Stock
Exchange Index (IBOVESPA) and show that the Heston model with stochastic
volatility is capable of explaining price fluctuations for time scales ranging
from 5 minutes to 100 days with a single set of parameters. We also show that
the Heston model is inconsistent with the observed behavior of the volatility
autocorrelation function. We deal with the latter inconsistency by introducing
a slow time scale to the model. The fact that the price dynamics in a period of
35 years of macroeconomical unrest may be modeled by the same stochastic
process is evidence for a general underlying microscopic market dynamics.Comment: 11 pages, 8 figures, subimitte
Renormalizability of pure Super Yang-Mills in the Wess-Zumino gauge in the presence of the local composite operators and
The Super Yang-Mills theory in the presence of the local
composite operator is analyzed in the Wess-Zumino gauge by employing the
Landau gauge fixing condition. Due to the superymmetric structure of the
theory, two more composite operators, and
, related to the susy variations of are also
introduced. A BRST invariant action containing all these operators is obtained.
An all order proof of the multiplicative renormalizability of the resulting
theory is then provided by means of the algebraic renormalization setup.
Though, due to the non-linear realization of the supersymmetry in the
Wess-Zumino gauge, the renormalization factor of the gauge field turns out to
be different from that of the gluino.Comment: 20 pages, no figure
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