Observable non-gaussianity from gauge field production in slow roll inflation, and a challenging connection with magnetogenesis

In any realistic particle physics model of inflation, the inflaton can be expected to couple to other fields. We consider a model with a dilaton-like coupling between a U(1) gauge field and a scalar inflaton. We show that this coupling can result in observable non-gaussianity, even in the conventional regime where inflation is supported by a single scalar slowly rolling on a smooth potential: the time dependent inflaton condensate leads to amplification of the large-scale gauge field fluctuations, which can feed-back into the scalar/tensor cosmological perturbations. In the squeezed limit, the resulting bispectrum is close to the local one, but it shows a sizable and characteristic quadrupolar dependence on the angle between the shorter and the larger modes in the correlation. Observable non-gaussianity is obtained in a regime where perturbation theory is under control. If the gauge field is identified with the electromagnetic field, the model that we study is a realization of the magnetogenesis idea originally proposed by Ratra, and widely studied. This identification (which is not necessary for the non-gaussianity production) is however problematic in light of a strong coupling problem already noted in the literature.Comment: 28 pages, no figures. Final versio

Measurement of Parity Violation in the Early Universe using Gravitational-wave Detectors

A stochastic gravitational-wave background (SGWB) is expected to arise from the superposition of many independent and unresolved gravitational-wave signals, of either cosmological or astrophysical origin. Some cosmological models (characterized, for instance, by a pseudo-scalar inflaton, or by some modification of gravity) break parity, leading to a polarized SGWB. We present a new technique to measure this parity violation, which we then apply to the recent results from LIGO to produce the first upper limit on parity violation in the SGWB, assuming a generic power-law SGWB spectrum across the LIGO sensitive frequency region. We also estimate sensitivity to parity violation of the future generations of gravitational-wave detectors, both for a power-law spectrum and for a model of axion inflation. This technique offers a new way of differentiating between the cosmological and astrophysical sources of the isotropic SGWB, as astrophysical sources are not expected to produce a polarized SGWB.Comment: 5 pages, 2 figures, 1 tabl

BRANECODE: A Program for Simulations of Braneworld Dynamics

We describe an algorithm and a C++ implementation that we have written and made available for calculating the fully nonlinear evolution of 5D braneworld models with scalar fields. Bulk fields allow for the stabilization of the extra space. However, they complicate the dynamics of the system, so that analytic calculations (performed within an effective 4D theory) are typically only reliable close to stabilized configurations or when the evolution of the extra space is negligible. In the general case, a numerical study of the 5D equations is necessary, and the algorithm and code we describe are the first ones designed for this task. The program and its full documentation are available on the Web at http://www.cita.utoronto.ca/~jmartin/BRANECODE/. In this paper we provide a brief overview of what the program does and how to use it.Comment: 5 pages, 2 figure

The Ineludible non-Gaussianity of the Primordial Black Hole Abundance

We study the formation of primordial black holes when they are generated by the collapse of large overdensities in the early universe. Since the density contrast is related to the comoving curvature perturbation by a nonlinear relation, the overdensity statistics is unavoidably non-Gaussian. We show that the abundance of primordial black holes at formation may not be captured by a perturbative approach which retains the first few cumulants of the non-Gaussian probability distribution. We provide two techniques to calculate the non-Gaussian abundance of primordial black holes at formation, one based on peak theory and the other on threshold statistics. Our results show that the unavoidable non-Gaussian nature of the inhomogeneities in the energy density makes it harder to generate PBHs. We provide simple (semi-)analytical expressions to calculate the non-Gaussian abundances of the primordial black holes and show that for both narrow and broad power spectra the gaussian case from threshold statistics is reproduced by increasing the amplitude of the power spectrum by a factor ${\cal O}(2\div 3)$.Comment: 26 pages, 10 figures, matching published versio

Testing Primordial Black Holes as Dark Matter through LISA

The idea that primordial black holes (PBHs) can comprise most of the dark matter of the universe has recently reacquired a lot of momentum. Observational constraints, however, rule out this possibility for most of the PBH masses, with a notable exception around $10^{-12} M_\odot$. These light PBHs may be originated when a sizeable comoving curvature perturbation generated during inflation re-enters the horizon during the radiation phase. During such a stage, it is unavoidable that gravitational waves (GWs) are generated. Since their source is quadratic in the curvature perturbations, these GWs are generated fully non-Gaussian. Their frequency today is about the mHz, which is exactly the range where the LISA mission has the maximum of its sensitivity. This is certainly an impressive coincidence. We show that this scenario of PBHs as dark matter can be tested by LISA by measuring the GW two-point correlator. On the other hand, we show that the short observation time (as compared to the age of the universe) and propagation effects of the GWs across the perturbed universe from the production point to the LISA detector suppress the bispectrum to an unobservable level. This suppression is completely general and not specific to our model.Comment: 22 pages, 12 figures. v3: matching published versio

Post-Inflationary Gravitino Production Revisited

We revisit gravitino production following inflation. As a first step, we review the standard calculation of gravitino production in the thermal plasma formed at the end of post-inflationary reheating when the inflaton has completely decayed. Next we consider gravitino production prior to the completion of reheating, assuming that the inflaton decay products thermalize instantaneously while they are still dilute. We then argue that instantaneous thermalization is in general a good approximation, and also show that the contribution of non-thermal gravitino production via the collisions of inflaton decay products prior to thermalization is relatively small. Our final estimate of the gravitino-to-entropy ratio is approximated well by a standard calculation of gravitino production in the post-inflationary thermal plasma assuming total instantaneous decay and thermalization at a time $t \simeq 1.2/\Gamma_\phi$. Finally, in light of our calculations, we consider potential implications of upper limits on the gravitino abundance for models of inflation, with particular attention to scenarios for inflaton decays in supersymmetric Starobinsky-like models.Comment: 34 pages, 7 figures, uses psfra

Exact identification of the radion and its coupling to the observable sector

Braneworld models in extra dimensions can be tested in laboratory by the coupling of the radion to the Standard Model fields. The identification of the radion as a canonically normalized field involves a careful General Relativity treatment: if a bulk scalar is responsible for the stabilization of the system, its fluctuations are entangled with the perturbations of the metric and they also have to be taken into account (similarly to the well-developed theory of scalar metric perturbations in 4D cosmology with a scalar field). Extracting a proper dynamical variable in a warped geometry/scalar setting is a nontrivial task, performed so far only in the limit of negligible backreaction of the scalar field on the background geometry. We perform the general calculation, diagonalizing the action up to second order in the perturbations and identifying the physical eigenmodes of the system for any amplitude of the bulk scalar. This computation allows us to derive a very simple expression for the exact coupling of the eigenmodes to the Standard Model fields on the brane, valid for an arbitrary background configuration. As an application, we discuss the Goldberger-Wise mechanism for the stabilization of the radion in the Randall-Sundrum type models. The existing studies, limited to small amplitude of the bulk scalar field, are characterized by a radion mass which is significantly below the physical scale at the observable brane. We extend them beyond the small backreaction regime. For intermediate amplitudes, the radion mass approaches the electroweak scale, while its coupling to the observable brane remains nearly constant. At very high amplitudes, the radion mass instead decreases, while the coupling sharply increases. Severe experimental constraints are expected in this regime.Comment: 20 pages, 6 figure

Sistema de cultivo e custo de produção de feijoeiro comum em Primavera do Leste (MT), na safra 2004/2005.

O presente trabalho teve como objetivos: (a) caracterizar o sistema de cultivo de feijoeiro comum praticado em Primavera do Leste (MT); e (b) estimar o custo de produção de feijoeiro comum deste sistema de cultivo na safra 2004/2005.bitstream/CNPAF/23590/1/comt_101.pd

Emergent Gravity from a Mass Deformation in Warped Spacetime

We consider a deformation of five-dimensional warped gravity with bulk and boundary mass terms to quadratic order in the action. We show that massless zero modes occur for special choices of the masses. The tensor zero mode is a smooth deformation of the Randall-Sundrum graviton wavefunction and can be localized anywhere in the bulk. There is also a vector zero mode with similar localization properties, which is decoupled from conserved sources at tree level. Interestingly, there are no scalar modes, and the model is ghost-free at the linearized level. When the tensor zero mode is localized near the IR brane, the dual interpretation is a composite graviton describing an emergent (induced) theory of gravity at the IR scale. In this case Newton's law of gravity changes to a new power law below the millimeter scale, with an exponent that can even be irrational.Comment: 44 pages, 3 figure

Braneworld dynamics with the BRANECODE

We give a full nonlinear numerical treatment of time-dependent 5D braneworld geometry, which is determined self-consistently by potentials for the scalar field in the bulk and at two orbifold branes, supplemented by boundary conditions at the branes. We describe the BRANECODE, an algorithm which we designed to solve the dynamical equations numerically. We apply the BRANECODE to braneworld models and find several novel phenomena of the brane dynamics. Starting with static warped geometry with de Sitter branes, we find numerically that this configuration is often unstable due to a tachyonic mass of the radion during inflation. If the model admits other static configurations with lower values of de Sitter curvature, this effect causes a violent restructuring towards them, flattening the branes, which appears as a lowering of the 4D effective cosmological constant. Braneworld dynamics can often lead to brane collisions. We find that, in the presence of the bulk scalar field, the 5D geometry between colliding branes approaches a universal, homogeneous, anisotropic strong gravity Kasner-like asymptotic, irrespective of the bulk or brane potentials. The Kasner indices of the brane directions are equal to each other but different from that of the extra dimension