1,721,705 research outputs found
Leptogenesis via preheating
No full textLeptogenesis constitues a very simple scenario to achieve the baryon asymmetry that we observe today. It requires only the presence of right handed neutrinos (which arise very naturally in many extensions of the Standard Model) and depends crucially on the mechanism responsible for their production. In particular, when their mass exceeds the inflaton mass (1013 GeV in chaotic inflation) only non perturbative production can occur. It is shown here that non perturbative production of fermions in an expanding Universe is a very efficient mechanism up to masses of order of (1017 - 1018) GeV, and that it can be easily applied to solve the baryon asymmetry problem
Can broken rotational invariance be reconciled with inflation?
No full textMotivated by claims of broken rotational invariance in the WMAP data, a number of models have appeared in the literature realizing this effect through vector field(s) with a nonvanishing spatial vacuum expectation value. We discuss why many such models have ghost instabilities
Breaking of statistical isotropy and signatures of vector fields during inflation
No full textWe review work related to the breaking of statistical isotropy during inflation due to the presence of a vector field carrying a coherent vacuum expectation value over our Hubble patch. We also review isotropic signatures of vector fields during inflation
Inflation and leptogenesis from right handed sneutrinos in supergravity
No full textWe describe a supergravity model of inflation where the inflaton is identified with one linerar combination of two right handed sneutrino fields. The potential along the inflationary trajectory is flatter than that of massive chaotic inflation, resulting in a detectable but not ruled out tensor-to-scalar ratio r. In general, the potential for the two sneutrinos has complex phases. As a result, the two neutrinos can develop a nonvanishing lepton charge through a simple modification of the Affleck-Dine mechanism. [This talk summarizes the work of Evans, Ghergetta, and Peloso, Phys. Rev. D 92, no. 2, 021303 (2015) (Ref. 1). Please refer to that work for details and for a more comprehensive list of references.
CMB non-gaussianity from vector fields
No full textThe Planck satellite has recently measured the CMB temperature anisotropies with unprecedented accuracy, and it has provided strong bounds on primordial non-gaussianity. Such bounds constrain models of inflation, and mechanisms that produce the primordial perturbations. We discuss the non-gaussian signatures from the interactions of the inflation φ with spin-1 fields. We study the two different cases in which the inflaton is (i) a pseudo-scalar field with a φF̃F/fa interaction with a vector field, and (ii) a scalar field with a f (φ)F2 interaction. In the first case we obtain the strong limit fa ≳ 1016GeV on the decay constant. In the second case, specific choices of the function f (φ) can lead to a non-gaussianity with a characteristic shape not encountered in standard models of scalar field inflation, and which has also been constrained by Planck
ET sensitivity to the anisotropic Stochastic Gravitational Wave Background
No full textWe study the sensitivity of a pair of Einstein Telescopes (ET) (hypothetically located at the two sites currently under consideration for ET) to the anisotropies of the Stochastic Gravitational Wave Background (SGWB). We focus on the l =0,2,4 multipoles of an expansion of the SGWB in spherical harmonics, since the sensitivity to other multipoles is suppressed due to the fact that this pair of detector operates in a regime for which the product between the observed frequency and the distance between the two sites is much smaller than one. In this regime, the interferometer overlap functions for the anisotropic signal acquire very simple analytic expressions. These expressions can also be applied to any other pairs of interferometers (each one of arbitrary opening angle between its two arms) operating in this regime. Once the measurements at the vertices of the two sites are optimally combined, the sensitivity to the multipoles of the SGWB depends only on the latitude of the two sites, on the difference of their longitude, but not on the orientation of their arms
Moving sources in a ghost condensate
No full textGhost condensation has been recently proposed as a mechanism inducing the spontaneous breaking of Lorentz symmetry. Corrections to the Newton potential generated by a static source have been computed: they yield a limit M less than or similar to 10 MeV on the symmetry breaking scale, and-if the limit is saturated-they are maximal at a distance L similar to 1000 km from the source. However, these corrections propagate at a tiny velocity, nu(s) similar to 10(-12) m/s, many orders of magnitude smaller than the velocity of any plausible source. We compute the gravitational potential taking the motion of the source into account: the standard Newton law is recovered in this case, with negligible corrections for any distance from the source up to astrophysical scales. Still, the vacuum of the theory is unstable, and requiring stability over the lifetime of the Universe imposes a limit on M which is not too far from the one given above. In the absence of a direct coupling of the ghost to matter, signatures of this model will have to be searched in the form of exotic astrophysical events
Quintessence from shape moduli
No full textWe show that shape moduli in submillimeter extra dimensional scenarios, addressing the gauge hierarchy problem, can dominate the energy density of the Universe today. In our scenario, the volume of the extra dimensions is stabilized at a sufficiently high scale to avoid conflicts with nucleosynthesis and solar-system precision gravity experiments, while the shape moduli remain light but couple extremely weakly to brane-localized matter and easily avoid these bounds. Nonlocal effects in the bulk of the extra dimensions generate a potential for the shape moduli. The potential has the right form and order of magnitude to account for the present day cosmic acceleration, in a way analogous to models of quintessence as a pseudo Nambu-Goldstone boson
Remarks on the Boomerang results, the baryon density, and the leptonic asymmetry
No full textThe very recent Boomerang results give an estimate of unprecedented precision of the cosmic microwave background anisotropies on subdegree scales. A puzzling feature for theoretical cosmology is the low amplitude of the second acoustic peak. Through a qualitative discussion, we argue that a scarcely considered category of flat models, with a leptonic asymmetry, a high baryon density and a low cosmological constant seems to be in very good agreement with the data, while still being compatible with big bang nucleosynthesis and some other observational constraints. Although this is certainly not the only way to explain the data, we believe that these models deserve to be included in forthcoming likelihood analyses
Stability analysis of chromo-natural inflation and possible evasion of Lyth's bound
No full textWe perform the complete stability study of the model of chromo-natural inflation by Adshead and Wyman [Phys. Rev. Lett. 108, 261302 (2012)], where, due to its coupling to a SU(2) vector, a pseudoscalar inflaton χ slowly rolls on a steep potential. As a typical example, one can consider an axion with a sub-Planckian decay constant f. The model was recently studied by Dimastrogiovanni, Fasiello, and Tolley [J. Cosmol. Astropart. Phys. 02, 046 (2013)] in the mg ≫ H limit, where mg is the mass of the fluctuations of the vector field, and H the Hubble rate. We show that the inflationary solution is stable for
mg > 2 H, while it otherwise experiences a strong instability due to scalar perturbations in the subhorizon regime. The tensor perturbations are instead enhanced at large mg, while the vector ones remain perturbatively small. Depending on the parameters, this model can give a chiral gravity wave signal that can be detected in ongoing or forthcoming cosmic microwave background experiments. This detection can occur even if, during inflation, the inflaton spans an interval of size Δχ=O(f) which is some orders of magnitude below the Planck scale, evading a well known bound that holds for a free inflaton by Lyth [Phys. Rev. Lett. 78, 1861 (1997)]. The spectral tilt of the scalar perturbations typically decreases with decreasing mg. Therefore the simultaneous requirements of stability, sufficiently small tensor-to-scalar ratio, and sufficiently flat scalar spectrum can pose nontrivial bounds on the parameters of the model
- …
