F. Urban

Non-minimal CW inflation, electroweak symmetry breaking and the 750 GeV anomaly

A bstractWe study whether the hinted 750 GeV resonance at the LHC can be a Coleman-Weinberg inflaton which is non-minimally coupled to gravity. Since the inflaton must couple to new charged and coloured states to reproduce the LHC diphoton signature, the same interaction can generate its effective potential and trigger the electroweak symmetry breaking via the portal coupling to the Higgs boson. This inflationary scenario predicts a lower bound on the tensor-to-scalar ratio of r ≳ 0.006, where the minimal value corresponds to the measured spectral index ns ≃ 0.97. However, we find that the compatibility with the LHC diphoton signal requires exotic new physics at energy scales accessible at the LHC. We study and quantify the properties of the predicted exotic particles.

New Limits on Extragalactic Magnetic Fields from Rotation Measures

We take advantage of the wealth of rotation measures data contained in the NRAO VLA Sky Survey catalog to derive new, statistically robust, upper limits on the strength of extragalactic magnetic fields. We simulate the extragalactic magnetic field contribution to the rotation measures for a given field strength and correlation length, by assuming that the electron density follows the distribution of Lyman-α clouds. Based on the observation that rotation measures from distant radio sources do not exhibit any trend with redshift, while the extragalactic contribution instead grows with distance, we constrain fields with Jeans length coherence length to be below 1.7xa0nG at the 2σ level, and fields coherent across the entire observable Universe below 0.65xa0nG. These limits do not depend on the particular origin of these cosmological fields.

Bigravitational origin of dark matter

Observational evidence for dark matter is limited to gravitational effects. Dedicated searches have yielded null results, challenging the most popular models. This can be explained if cold dark matter is a massive spin-2 particle and, thus, a manifestation of gravity itself. In the unique consistent theory for a massless and a massive spin-2 field, the latter can be heavy, stable on cosmological scales, and produced with correct abundance, and its matter coupling is naturally as weak as the gravitational one. The theory satisfies current gravity tests, and we suggest several gravitational signatures.

Heavy spin-2 Dark Matter

We provide further details on a recent proposal addressing the nature of the dark sectors in cosmology and demonstrate that all current observations related to Dark Matter can be explained by the presence of a heavy spin-2 particle. Massive spin-2 fields and their gravitational interactions are uniquely described by ghost-free bimetric theory, which is a minimal and natural extension of General Relativity. In this setup, the largeness of the physical Planck mass is naturally related to extremely weak couplings of the heavy spin-2 field to baryonic matter and therefore explains the absence of signals in experiments dedicated to Dark Matter searches. It also ensures the phenomenological viability of our model as we confirm by comparing it with cosmological and local tests of gravity. At the same time, the spin-2 field possesses standard gravitational interactions and it decays universally into all Standard Model fields but not into massless gravitons. Matching the measured DM abundance together with the requirement of stability constrains the spin-2 mass to be in the 1 to 100 TeV range.

Mapping ultrahigh energy cosmic rays deflections through the turbulent galactic magnetic field with the latest rotation measure data

We study the influence of the random part of the Galactic magnetic field on the propagation of ultra high-energy cosmic rays. Within very mild approximations about the properties of the electron density fluctuations in the Galaxy we are able to derive a clear and direct relation between the observed variance of rotation measures and the predicted cosmic ray deflections. Remarkably, this is obtained bypassing entirely the detailed knowledge of the magnetic properties of the turbulent plasma. Depending on the parameters of the electron density spectrum, we can either directly estimate the expected deflection, or constrain it from above. Thanks to the latest observational data on rotation measures, we build a direction-dependent map of such deflections. We find that over most of the sky the random deflections of 40 EeV protons do not exceed 1 to 2 degrees, and can be as large as 5 degrees close to the Galactic plane.

Perturbations and non-Gaussianities in three-form inflationary magnetogenesis

We reconsider magnetogenesis in the context of three-form inflation, and its backreaction. In particular, we focus on first order perturbation theory during inflation and subsequent radiation era: we discuss the consistency of the perturbative approach, and elaborate on the possible non-Gaussian signatures of the model.

Statistics of anisotropies in inflation with spectator vector fields

We study the statistics of the primordial power spectrum in models where massless gauge vectors are coupled to the inflaton, paying special attention to observational implications of having fundamental or effective horizons embedded in a bath of infrared fluctuations. As quantum infrared modes cross the horizon, they classicalize and build a background vector field. We find that the vector experiences a statistical precession phenomenon. Implications for primordial correlators and the interpretation thereof are considered. Firstly, we show how in general two, not only one, additional observables, a quadrupole amplitude and an intrinsic shape parameter, are necessary to fully describe the correction to the curvature power spectrum, and develop a unique parametrization for them. Secondly, we show that the observed anisotropic amplitude and the associated preferred direction depend on the volume of the patch being probed. We calculate non-zero priors for the expected deviations between detections based on microwave background data (which probes the entire Hubble patch) and large scale structure (which only probes a fraction of it).

Cosmic magnetization in three-form inflation

A completely new mechanism to generate the observed amount of large-scale cosmological magnetic fields is introduced in the context of three-form inflation. The amplification of the fields occurs via fourth order dynamics of the vector perturbations and avoids the backreaction problem that plagues most previously introduced mechanisms.

The Parity Odd Universe, Dark Energy and QCD

Cosmological observations on the largest scales exhibit a solid record of unexpected anomalies and alignments, apparently pointing towards a large scale violation of statistical isotropy. These include a variety of CMB measurements, as well as alignments of quasar polarisation vectors. In this paper we explore the possibility that several of the aforementioned large scale correlations are in fact not independent, and can be understood in a coherent way within the framework of a parity odd local Universe, and ultimately related to the nature of Dark Energy and its interactions with light.

Pseudoscalar N-flation and axial coupling revisited

We revisit the dynamics of the axial coupling between many N-flatons and an Abelian gauge field, with special attention to its statistically anisotropic signal. The anisotropic power spectrum of curvature perturbations associated with the large-wavelength modes of the gauge vector field is generally undetectable, since the anisotropy is confined to small scales. If the gauge field is the electromagnetic field, provided that the number of fields participating in the exponential expansion is large, it could be possible to generate sizable large-scale magnetic fields. However, its spectrum is blue, and appreciable power on large scales implies an overly strong field on smaller scales, incompatible with observations. Furthermore, the anisotropy is also markedly enhanced, and might be at odds with the isotropic observed sky. These aspects further demand that the scale of inflation be kept to a minimum.