Higher Spins and Current Exchanges

The simplest higher-spin interactions involve classical external currents and symmetric tensors \phi_{\m_1 ... \m_s}, and convey three instructive lessons. The first is a general form of the van Dam-Veltman-Zakharov discontinuity in flat space for this class of fields. The second is the rationale for its disappearance in (A)dS spaces. Finally, the third is a glimpse into an option which is commonly overlooked in Field Theory, and which both higher spins and String Theory are confronting us with: one can well allow in the Lagrangians non-local terms that do not spoil the local nature of physical quantities.Comment: 7 pages, LATEX. Lecture presented at the 9th Hellenic School on Elementary Particle Physics and Gravity, Corfu 200

Brane SUSY Breaking and Inflation: Implications for Scalar Fields and CMB Distorsion

I elaborate on a link between the string--scale breaking of supersymmetry that occurs in a class of superstring models and the onset of inflation. The link rests on spatially flat cosmologies supported by a scalar field driven by an exponential potential. If, as in String Theory, this potential is steep enough, under some assumptions that are spelled out in the text the scalar can only climb up as it emerges from an initial singularity. In the presence of another mild exponential, slow--roll inflation is thus injected during the ensuing descent and definite imprints are left in the CMB power spectrum: the quadrupole is systematically reduced and, depending on the choice of two parameters, an oscillatory behavior can also emerge for low multipoles l < 50, in qualitative agreement with WMAP9 and PLANCK data. The experimentally favored value of the spectral index, n_s ~ 0.96, points to a potentially important role for the NS fivebrane, which is unstable in this class of models, in the Early Universe.Comment: 9 pages, 4 figures. The original version was based on the talk presented at Rencontres de Moriond EW2013, La Thuile, March 2 - 9 2013. The new version is also based on the talks presented at the "Two-day PLANCK Meeting" and at the "18th Claude Itzykson Meeting". It includes some improved plots and a discussion of the possible role of more general brane

Some Pathways in non-Linear Supersymmetry: Special Geometry Born-Infeld's, Cosmology and dualities

This review is devoted to some aspects of non-linear Supersymmetry in four dimensions that can be efficiently described via nilpotent superfields, in both rigid and curved Superspace. Our focus is mainly on the partial breaking of rigid $N=2$ Supersymmetry and on a class of generalized Born-Infeld systems that originate from Special Geometry and on some prototype cosmological models, starting from the Supergravity embedding of Starobinsky inflation. However, as an aside we also review briefly some interesting two-field extensions of the Born-Infeld Lagrangian whose field equations enjoy extended duality symmetries.Comment: Contribution to the Proceedings of "Group Theory, Probability, and the Structure of Spacetime", A Conference on the Occasion of Professor V.S. Varadarajan's Retirement, UCLA Mathematics Department, November 7-9, 2014. To appear in a special issue of "p-Adic Numbers, Ultrametric Analysis and Applications". 35 pages LaTeX, 1 eps figure. Typos corrected, reference adde

Observational Hints of a Pre--Inflationary Scale?

We argue that the lack of power exhibited by cosmic microwave background (CMB) anisotropies at large angular scales might be linked to the onset of inflation. We highlight observational features and theoretical hints that support this view, and present a preliminary estimate of the physical scale that would underlie the phenomenon.Comment: 7 pages, LaTeX, 2 eps figures. Essay Written for the 2015 Gravity Research Foundation Awards for Essays on Gravitation. Selected for Honorable Mentio