Dynamical symmetries, coherent states and nonlinear realizations: The SO(2,4) case

Nonlinear realizations of the [Formula: see text] group are discussed from the point of view of symmetries. Dynamical symmetry breaking is introduced. One linear and one quadratic model in curvature are constructed. Coherent states of the Klauder–Perelomov type are defined for both cases taking into account the coset geometry. A new spontaneous compactification mechanism is defined in the subspace invariant under the stability subgroup. The physical implications of the symmetry rupture in the context of nonlinear realizations and direct gauging are analyzed and briefly discussed.

Low-ℓ CMB from string-scale SUSY breaking?

Models of inflation are instructive playgrounds for supersymmetry (SUSY) breaking in Supergravity and String Theory. In particular, combinations of branes and orientifolds that are not mutually BPS can lead to brane SUSY breaking, a phenomenon where nonlinear realizations are accompanied, in tachyon-free vacua, by the emergence of steep exponential potentials. When combined with milder terms, these exponentials can lead to slow-roll after a fast ascent and a turning point. This leaves behind distinctive patterns of scalar perturbations, where pre-inflationary peaks can lie well apart from an almost scale invariant profile. I review recent attempts to connect these power spectra to the low-[Formula: see text] cosmic microwave background (CMB), and a corresponding one-parameter extension of Lambda cold dark matter ([Formula: see text]CDM) with a low-frequency cut [Formula: see text]. A detailed likelihood analysis led to [Formula: see text], at 99.4% confidence level, in an extended Galactic mask with [Formula: see text], to be compared with a nearby value at 88.5% in the standard Planck 2015 mask with [Formula: see text]. In these scenarios, one would be confronted, in the CMB, with relics of an epoch of deceleration that preceded the onset of slow-roll.