Inflation in R2R^2 supergravity with non-minimal superpotentials

We investigate the cosmological inflation in a class of supergravity models that are generalizations of non-supersymmetric $R^2$ models. Although such models have been extensively studied recently, especially after the launch of the PLANCK and BICEP2 data, the class of models that can be constructed has not been exhausted. In this note, working in a supergravity model that is a generalization of Cecotti's model, we show that the appearance of new superpotential terms, which are quadratic in the superfield $\, \Lambda$ that couples to the Ricci supermultiplet, alters substantially the form of the scalar potential. The arising potential has the form of the Starobinsky potential times a factor that is exponential in the inflaton field and dominates for large inflaton values. We show that the well-known Starobinsky inflation scenario is maintained only for unnaturally small fine-tuned values of the coupling describing the $\Lambda^2$ superpotential terms. A welcome feature is the possible increase of the tensor to scalar ratio $r$, within the limits set by the new Planck and BICEP2 data.Comment: 13 pages, 9 figures, text and references added, version submitted to Phys. Lett.

On the radion mediation of the Supersymmetry breaking in N=2, D=5 Supergravity Orbifolds

We discuss the on-shell N=1 Supersymmetric coupling of brane chiral multiplets in the context of N=2, D=5 Supergravity compactified on $S_1/Z_2$ orbifolds. Assuming a constant superpotential on the hidden brane we study the transmission of the supersymmetry breaking to the visible brane. We find that to lowest order in the five dimensional Newton's constant $k_5^2$ and gravitino mass $m_{3/2}^2$ the spinor field of the radion multiplet is responsible of inducing positive one-loop squared masses $m_{\phi}^2 \sim {m_{3/2}^2} / (M_{Planck}^2 R^2)$ to the scalar fields which are localized on the visible brane with $R$ the length scale of the fifth dimension. Considering a cubic superpotential on the visible brane we also find that non-vanishing soft trilinear scalar couplings $A$ are induced given by $A=3m_{\phi}^2/m_{3/2}$.Comment: 14 pages, 2 figures, version to appear in Physics Letters

On the Stability of the Classical Vacua in a Minimal SU(5) 5-D Supergravity Model

We consider a five-dimensional supergravity model with SU(5) gauge symmetry and the minimal field content. Studying the arising scalar potential we find that the gauging of the $U(1)_R$ symmetry of the five-dimensional supergravity causes instabilities. Lifting the instabilities the vacua are of Anti-de-Sitter type and SU(5) is broken along with supersymmetry. Keeping the $U(1)_R$ ungauged the potential has flat directions along which supersymmetry is unbroken.Comment: 24 pages, 2 figure

The soft supersymmetry breaking in D=5 supergravity compactified on S_1/Z_2 orbifolds

We study the origin of the supersymmetry breaking induced by the mediation of gravity and the radion multiplet from the hidden to the visible brane in the context of the N=2, D=5 supergravity compactified on S_1/Z_2 orbifolds. The soft supersymmetry breaking terms for scalar masses, trilinear scalar couplings and gaugino masses are calculated to leading order in the five dimensional Newton's constant k_5^2 and the gravitino mass m_{3/2}. These are finite and non-vanishing, with the scalar soft masses be non-tachyonic, and are all expressed in terms of the gravitino mass and the length scale R of the fifth dimension. The soft supersymmetry breaking parameters are thus correlated and the phenomenological implications are discussed.Comment: 16 pages, 3 figures, 1 Table, final version to appear in Physics Letters B, slightly shortened, comments added, typos correcte

On the brane coupling of unified orbifolds with gauge interactions in the bulk

In the on-shell formulation of D=5, N=2 supergravity, compactified on S 1/Z 2, we extend the results of Mirabelli and Peskin describing the interaction of the bulk fields with matter which is assumed to be confined on the brane. The novel characteristics of this approach are: (i) Propagation of both gravity and gauge fields in the bulk, which offers an alternative for a unified description of models in extra dimensions and (ii) use of the on-shell formulation avoiding the complexity of off-shell schemes which involve numerous auxiliary fields. We also allow for non-trivial superpotential interactions of the chiral matter fields. The method we employ uses the Nöther procedure and our findings are useful for building models advocating propagation of the gauge degrees of freedom in the bulk, in addition to gravity. © 2004 Published by Elsevier B.V

On the radion mediation of the supersymmetry breaking in N = 2, D = 5 supergravity orbifolds

We discuss the on-shell N = 1 supersymmetric coupling of brane chiral multiplets in the context of N = 2, D = 5 supergravity compactified on S1 / Z2 orbifolds. Assuming a constant superpotential on the hidden brane we study the transmission of the supersymmetry breaking to the visible brane. We find that to lowest order in the five-dimensional Newton's constant k52 and gravitino mass m3 / 22 the spinor field of the radion multiplet is responsible of inducing positive one-loop squared masses mφ2 ∼ m3 / 22 / (MPlanck2 R2) to the scalar fields which are localized on the visible brane with R the length scale of the fifth dimension. Considering a cubic superpotential on the visible brane we also find that non-vanishing soft trilinear scalar couplings A are induced given by A = 3 mφ2 / m3 / 2. © 2008 Elsevier B.V. All rights reserved

Six-dimensional origin of gravity-mediated brane to brane supersymmetry breaking

Four-dimensional supergravities may be the right framework to describe particle physics at low energies. Its connection to the underlying string theory can be implemented through higher dimensional supergravities which bear special characteristics. Their reduction to four dimensions breaks supersymmetry whose magnitude depends both on the compactifying manifold and the mechanism that generates the breaking. In particular compactifications, notably on a S1/Z2 orbifold, the breaking of supersymmetry occurring on a hidden brane, residing at one end of S1/Z2, is communicated to the visible brane which lies at the other end, via gravitational interactions propagating in the bulk. This scenario has been exemplified in the framework of the N=2, D=5 supergravity. In this paper, motivated by the recent developments in the field, related to the six-dimensional description of the supergravity theory, we study the N=2, D=5 supergravity theory as originating from a D=6 supergravity which, in addition to the gravity, includes a number of tensor multiplets. This reduces to N=1, D=4 supergravity in a two step manner, first by a Kaluza-Klein reduction followed by a S1/Z2 orbifold compactification. The resulting theory has striking similarities with the one that follows from the single stand alone N=2, D=5 supergravity, with no reference to the underlying higher dimensional D=6 supergravity, and a structure that makes the supersymmetry breaking mechanisms studied in the past easily incorporated in higher dimensional schemes. © 2014 American Physical Society