Inflation and Conformal Invariance: The Perspective from Radial Quantization

According to the dS/CFT correspondence, correlators of fields generated during a primordial de Sitter phase are constrained by three-dimensional conformal invariance. Using the properties of radially quantized conformal field theories and the operator-state correspondence, we glean information on some points. The Higuchi bound on the masses of spin-s states in de Sitter is a direct consequence of reflection positivity in radially quantized CFT$_3$ and the fact that scaling dimensions of operators are energies of states. The partial massless states appearing in de Sitter correspond from the boundary CFT$_3$ perspective to boundary states with highest weight for the conformal group. We discuss inflationary consistency relations and the role of asymptotic symmetries which transform asymptotic vacua to new physically inequivalent vacua by generating long perturbation modes. We show that on the CFT$_3$ side, asymptotic symmetries have a nice quantum mechanics interpretation. For instance, acting with the asymptotic dilation symmetry corresponds to evolving states forward (or backward) in "time" and the charge generating the asymptotic symmetry transformation is the Hamiltonian itself. Finally, we investigate the symmetries of anisotropic inflation and show that correlators of four-dimensional free scalar fields can be reproduced in the dual picture by considering an isotropic three-dimensional boundary enjoying dilation symmetry, but with a nonvanishing vacuum expectation value of the boundary stress-energy momentum tensor.Comment: 41 pages, 4 figure

Frequentist analyses of solar neutrino data (updated including KamLAND and SNO data)

The solar neutrino data are analyzed in a frequentist framework, using the Crow-Gardner and Feldman-Cousins prescriptions for the construction of confidence regions. Including in the fit only the total rates measured by the various experiments, both methods give results similar to the commonly used Delta chi^2-cut approximation. When fitting the full data set, the Delta chi^2-cut still gives a good approximation of the Feldman-Cousins regions. However, a careful statistical analysis significantly reduces the goodness-of-fit of the SMA and LOW solutions. In the addenda we discuss the implications of the latest KamLAND, SNO and SK data.Comment: 24 pages, 12 figures. Version 2: addendum about the CC SNO data (section 6). Version 3: addendum about the NC and day/night SNO data (section 7). Version 4: addendum about the KamLAND data (section 8). Version 5: addendum about SNO salt data (section 9, pages 22, 23). Version 6: final addendum about final SNO salt data and KamLAND (section 10, page 24

Galilean Genesis: an alternative to inflation

We propose a novel cosmological scenario, in which standard inflation is replaced by an expanding phase with a drastic violation of the Null Energy Condition (NEC): \dot H >> H^2. The model is based on the recently introduced Galileon theories, that allow NEC violating solutions without instabilities. The unperturbed solution describes a Universe that is asymptotically Minkowski in the past, expands with increasing energy density until it exits the regime of validity of the effective field theory and reheats. This solution is a dynamical attractor and the Universe is driven to it, even if it is initially contracting. The study of perturbations of the Galileon field reveals some subtleties, related to the gross violation of the NEC and it shows that adiabatic perturbations are cosmologically irrelevant. The model, however, suggests a new way to produce a scale invariant spectrum of isocurvature perturbations, which can later be converted to adiabatic: the Galileon is forced by symmetry to couple to the other fields as a dilaton; the effective metric it yields on the NEC violating solution is that of de Sitter space, so that all light scalars will automatically acquire a nearly scale-invariant spectrum of perturbations.Comment: 25 pages, 1 figure. v2: minor changes, JCAP published versio

Stability of Geodesically Complete Cosmologies

We study the stability of spatially flat FRW solutions which are geodesically complete, i.e. for which one can follow null (graviton) geodesics both in the past and in the future without ever encountering singularities. This is the case of NEC-violating cosmologies such as smooth bounces or solutions which approach Minkowski in the past. We study the EFT of linear perturbations around a solution of this kind, including the possibility of multiple fields and fluids. One generally faces a gradient instability which can be avoided only if the operator $~^{(3)}{R} \delta N~$ is present and its coefficient changes sign along the evolution. This operator (typical of beyond-Horndeski theories) does not lead to extra degrees of freedom, but cannot arise starting from any theory with second-order equations of motion. The change of sign of this operator prevents to set it to zero with a generalised disformal transformation.Comment: 18 pages, 2 figures. v2: minor changes; references added; version published in JCA

Right-handed neutrinos as the source of density perturbations

We study the possibility that cosmological density perturbations are generated by the inhomogeneous decay of right-handed neutrinos. This will occur if a scalar field whose fluctuations are created during inflation is coupled to the neutrino sector. Robust predictions of the model are a detectable level of non-Gaussianity and, if standard leptogenesis is the source of the baryon asymmetry, a baryon isocurvature perturbations at the level of the present experimental constraints.Comment: 14 pages, 2 figure

Tensor Squeezed Limits and the Higuchi Bound

We point out that tensor consistency relations-i.e. the behavior of primordial correlation functions in the limit a tensor mode has a small momentum-are more universal than scalar consistency relations. They hold in the presence of multiple scalar fields and as long as anisotropies are diluted exponentially fast. When de Sitter isometries are approximately respected during inflation this is guaranteed by the Higuchi bound, which forbids the existence of light particles with spin: De Sitter space can support scalar hair but no curly hair. We discuss two indirect ways to look for the violation of tensor con- sistency relations in observations, as a signature of models in which inflation is not a strong isotropic attractor, such as solid inflation: (a) Graviton exchange contribution to the scalar four-point function; (b) Quadrupolar anisotropy of the scalar power spectrum due to super-horizon tensor modes. This anisotropy has a well-defined statistics which can be distinguished from cases in which the background has a privileged direction.Comment: 21 pages. v2: minor changes, matches JCAP versio

Consistency relation for single scalar inflation

Single scalar field inflation with a generic, non-quadratic in derivatives, field Lagrangian is considered. It is shown that non-Gaussianity of curvature perturbations is characterized by two dimensionless amplitudes. One of these amplitudes can be expressed in terms of the usual inflationary observables -- the scalar power, the tensor power, and the tensor index. This consistency relation provides an observational test for the single scalar inflation.Comment: 6 page