1,376 research outputs found
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 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
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