Natural Inflation from 5D SUGRA and Low Reheat Temperature

Motivated by recent cosmological observations of a possibly unsuppressed primordial tensor component $r$ of inflationary perturbations, we reanalyse in detail the 5D conformal SUGRA originated natural inflation model of Ref. [1]. The model is a supersymmetric variant of 5D extra natural inflation, also based on a shift symmetry, and leads to the potential of natural inflation. Coupling the bulk fields generating the inflaton potential via a gauge coupling to the inflaton with brane SM states we necessarily obtain a very slow gauge inflaton decay rate and a very low reheating temperature $T_r\stackrel{<}{_\sim }{\cal O}(100)$~GeV. Analysis of the required number of e-foldings (from the CMB observations) leads to values of $n_s$ in the lower range of present Planck 2015 results. Some related theoretical issues of the construction, along with phenomenological and cosmological implications, are also discussed.Comment: Analysis and discussions updated in light of recent Planck and joint analysis of BICEP2/Keck and Planck result

5D Supersymmetric Orbifolds: Supergravity/Phenomenological Aspects

Five-dimensional braneworlds attracted much attention in recent years, be it for phenomenological, cosmological or theoretical reasons. In this work we study supersymmetric theories compactified on the orbifold S1/Z2. We start with a short discussion of power-law unification, where 5D rigid super Yang-Mills theory is introduced in its superfield formulation. We develop a superfield description of 5D orbifold N = 2 supergravity coupled to vector and hyper multiplets. The basic building blocks are N = 1 supermultiplets obtained as reductions of the full multiplets of N = 2 conformal supersymmetry by Fujita, Kugo and Ohashi. After identifying the relevant superfields we build superspace actions for the vector, hyper and radion sectors. The couplings of these sectors to the 4D Weyl multiplet are obtained by the replacement of integrations over (flat) superspace by the F and D densities of 4D conformal supergravity. We then observe that a Weyl rescaling is enough to extend the formalism to warped geometries, and show how to consistently introduce brane-localized couplings. The superfield approach to 5D orbifold N = 2 supergravity is used to rederive the BPS conditions in the generalized Randall-Sundrum models without using the 4-form mechanism to introduce the odd couplings. It is noted that BPS conditions correspond to F and D flatness conditions, which are simple to obtain in this formalism. Next, a study of recent claims on supersymmetric radion stabilization leads us to speculate on a possible no-go theorem on this possibility. We then consider the supergravity embedding of tuned Fayet-Iliopoulos terms, show that they do not break supersymmetry even in warped geometries, and obtain new supersymmetric vacua with negative brane tensions and a bulk fat brane. We close with a study of supersymmetric models of gauge inflation

Hermitian Yang-Mills instantons on Calabi-Yau cones

We study and construct non-abelian hermitian Yang-Mills (HYM) instantons on Calabi-Yau cones. By means of a particular isometry preserving ansatz, the HYM equations are reduced to a novel Higgs-Yang-Mills flow on the Einstein-Kahler base. For any 2d-dimensional Calabi-Yau cone, we find explicit solutions of the flow equations that correspond to non-trivial SU(d) HYM instantons. These can be regarded as deformations of the spin connection of the Calabi-Yau cone.Comment: 17 page

F-term Uplift in Heterotic M-theory

We investigate the viability of F-term uplift in heterotic M-theory. With this aim we explore a natural ingredient of heterotic compactifications, namely vector bundle moduli. It is shown that it is generically possible to obtain stable de Sitter vacua with broken supersymmetry provided the little Kahler potential and the prefactors of the non-perturbative superpotential are suitably tuned. An additional requirement is the existence of non-trivial gauge instantons both at the visible and hidden sectors. This is illustrated with analytical and numerical examples.Comment: 21 pages, 1 figure, references added, typos correcte

Gauge and Modulus Inflation from 5D Orbifold SUGRA

We study the inflationary scenarios driven by a Wilson line field - the fifth component of a 5D gauge field and corresponding modulus field, within S^1/Z_2 orbifold supergravity (SUGRA). We use our off shell superfield formulation and give a detailed description of the issue of SUSY breaking by the F-component of the radion superfield. By a suitably gauged U(1)R symmetry and including couplings with compensator supermultiplets and a linear multiplet, we achieve a self consistent radion mediated SUSY breaking of no scale type. The inflaton 1-loop effective potential has attractive features needed for successful inflation. An interesting feature of both presented inflationary scenarios are the red tilted spectra with ns~0.96. For gauge inflation we obtain a significant tensor to scalar ratio r~0.1 of the density perturbations, while for the modulus inflation r is strongly suppressed.Comment: 14 pages, 1 figur

(BPS) Fayet-Iliopoulos Terms in 5D Orbifold SUGRA

We discuss Fayet-Iliopoulos terms in the context of five-dimensional supergravity compactified on an orbifold. For this purpose we use our superfield formulation of the off-shell 5D SUGRA. In the case of tuned FI terms, contrary to other claims, we find BPS solutions which ensure that N=1 supersymmetry is unbroken also in warped geometries. As in the rigid case, the FI terms induce odd masses for charged hypermultiplets, leading to the (de)localisation of the KK wave-functions near the fix-point branes. In the case of ungauged U(1)_R symmetry, we present also supersymmetric warped solutions in the presence of non-trivial profiles of charged hyperscalars.Comment: LaTeX, 11 pages, 2 figures, extended discussion after (25) and (49), version published in PL

Hermitian Yang-Mills instantons on resolutions of Calabi-Yau cones

We study the construction of Hermitian Yang-Mills instantons over resolutions of Calabi-Yau cones of arbitrary dimension. In particular, in d complex dimensions, we present an infinite family, parametrised by an integer k and a continuous modulus, of SU(d) instantons. A detailed study of their properties, including the computation of the instanton numbers is provided. We also explain how they can be used in the construction of heterotic non-Kahler compactifications.Comment: 20 pages, 1 figure; typos corrected, section 3.1 expande

4D Superfield Reduction of 5D Orbifold SUGRA and Heterotic M-theory

We present a detailed study of the reduction to 4D of 5D supergravity compactified on the S^1/Z_2 orbifold. For this purpose we develop and employ a recently proposed N=1 conformal superfield description of the 5D supergravity couplings to abelian vector and hypermultiplets. In particular, we obtain a unique relation of the "radion" to chiral superfields as in global 5D SUSY and we can embed the universal hypermultiplet into this formalism. In our approach, it is transparent how the superconformal structure of the effective 4D actions is inherited from the one of the original 5D supergravity. We consider both ungauged and gauged 5D supergravities. This includes compactifications in unwarped geometries, generalizations of the supersymmetric Randall-Sundrum (RS) model as well as 5D heterotic M-theory. In the unwarped case, after obtaining the effective Kaehler potentials and superpotentials, we demonstrate that the tree-level 4D potentials have flat and/or tachyonic directions. One-loop corrections to the Kaehler potential and gaugino condensation are presented as suitable tools for moduli stabilization to be discussed in subsequent work. Turning to the RS-like models, we obtain a master formula for the Kaehler potential for an arbitrary number of vector and hyper moduli, which we evaluate exactly for special cases. Finally, we formulate the superfield description of 5D heterotic M-theory and obtain its effective 4D description for the universal (h^(1,1)=1) case, in the presence of an arbitrary number of bulk 5-branes. We present, as a check of our expressions, time-dependent solutions of 4D heterotic M-theory, which uplift to 5D solutions generalizing the ones recently found in hep-th/0502077.Comment: 39 pages, references added, version to appear in NP