Longevity of supersymmetric flat directions

We examine the fate of supersymmetric flat directions. We argue that the non-perturbative decay of the flat direction via preheating is an unlikely event. In order to address this issue, first we identify the physical degrees of freedom and their masses in presence of a large flat direction VEV (Vacuum Expectation Value). We explicitly show that the (complex) flat direction and its fermionic partner are the only light {\it physical} fields in the spectrum. If the flat direction VEV is much larger than the weak scale, and it has a rotational motion, there will be no resonant particle production at all. The case of multiple flat directions is more involved. We illustrate that in many cases of physical interest, the situation becomes effectively the same as that of a single flat direction, or collection of independent single directions. In such cases preheating is not relevant. In an absence of a fast non-perturbative decay, the flat direction survives long enough to affect thermalization in supersymmetric models as described in hep-ph/0505050 and hep-ph/0512227. It can also ``terminate'' an early stage of non-perturbative inflaton decay as discussed in hep-ph/0603244.Comment: 9 revtex pages, v3: expanded discussion on two flat directions, minor modifications, conclusions unchange

Inflection point inflation within supersymmetry

We propose to address the fine tuning problem of inflection point inflation by the addition of extra vacuum energy that is present during inflation but disappears afterwards. We show that in such a case, the required amount of fine tuning is greatly reduced. We suggest that the extra vacuum energy can be associated with an earlier phase transition and provide a simple model, based on extending the SM gauge group to SU(3)_C \times SU(2)_L\times U(1)_Y\times U(1)_{B-L}, where the Higgs field of U(1)_{B-L} is in a false vacuum during inflation. In this case, there is virtually no fine tuning of the soft SUSY breaking parameters of the flat direction which serves as the inflaton. However, the absence of radiative corrections which would spoil the flatness of the inflaton potential requires that the U(1)_{B-L} gauge coupling should be small with g_{B-L}\leq 10^{-4}.Comment: 6 pages, 1 figur

A-term inflation and the smallness of the neutrino masses

The smallness of the neutrino masses may be related to inflation. The minimal supersymmetric Standard Model (MSSM) with small Dirac neutrino masses already has all the necessary ingredients for a successful inflation. In this model the inflaton is a gauge-invariant combination of the right-handed sneutrino, the slepton, and the Higgs field, which generate a flat direction suitable for inflation if the Yukawa coupling is small enough. In a class of models, the observed microwave background anisotropy and the tilted power spectrum are related to the neutrino masses.Comment: 13 pages, 1 figure, uses JHEP3.cls, minor modifications, final version accepted for publication in JCA

Identifying the curvaton within MSSM

We consider inflaton couplings to MSSM flat directions and the thermalization of the inflaton decay products, taking into account gauge symmetry breaking due to flat direction condensates. We then search for a suitable curvaton candidate among the flat directions, requiring an early thermally induced start for the flat direction oscillations to facilitate the necessary curvaton energy density dominance. We demonstrate that the supersymmetry breaking $A$-term is crucial for achieving a successful curvaton scenario. Among the many possible candidates, we identify the ${\bf u_1dd}$ flat direction as a viable MSSM curvaton.Comment: 9 pages. Discussion on the evaporation of condensate added, final version published in JCA

Inflation from IIB Superstrings with Fluxes

We study the conditions needed to have an early epoch of inflationary expansion with a potential coming from IIB superstring theory with fluxes involving two moduli fields. The phenomenology of this potential is different from the usual hybrid inflation scenario and we analize the possibility that the system of field equations undergo a period of inflation in three different regimes with the dynamics modified by a Randall-Sundrum II term in the Friedmann equation. We find that the system can produce inflation and due to the modification of the dynamics, a period of accelerated contraction can follow or preceed this inflationary stage depending on the sign of one of the parameters of the potential. We discuss on the viability of this model in a cosmological context.Comment: 10 pages, 6 figure

Inflection point inflation: WMAP constraints and a solution to the fine-tuning problem

We consider observational constraints and fine-tuning issues in a renormalizable model of inflection point inflation, with two independent parameters. We derive constraints on the parameter space of this model arising from the WMAP 7-year power spectrum. It has previously been shown that it is possible to successfully embed this potential in the MSSM. Unfortunately, to do this requires severe fine-tuning. We address this issue by introducing a hybrid field to dynamically uplift the potential with a subsequent smooth phase transition to end inflation at the necessary point. Large parameter regions exist where this drastically reduces the fine-tuning required without ruining the viability of the model. A side effect of this mechanism is that it increases the width of the slow-roll region of the potential, thus also alleviating the problem of the fine-tuning of initial conditions. The MSSM embedding we study has been previously shown to be able to explain the smallness of the neutrino masses. The hybrid transition does not spoil this feature as there exist parameter regions where the fine-tuning parameter is as large as $10^{-1}$ and the neutrino masses remain small.Comment: 12 pages, 2 figures, JCAP style. Version accepted for publication in JCAP. Modifications made to improve readability, as requested by the referee; results and conclusions unchanged. References update

Reheating and Supersymmetric Flat-Direction Baryogenesis

We re-examine Affleck-Dine baryo/leptogenesis from the oscillation of condensates along flat directions of the supersymmetric standard model, which attained large vevs at the end of inflationary epoque. The key observation is that superpotential interactions couple the flat directions to other fields, which acquire masses induced by the flat-direction vev that may be sufficiently small for them to be kinematically accessible to inflaton decay. The resulting plasma of inflaton decay products then may act on the flat directions via these superpotential Yukawa couplings, inducing thermal masses and supersymmetry-breaking A terms. In such cases the flat directions start their oscillations at an earlier time than usually estimated. The oscillations are also terminated earlier, due to evaporation of the flat direction condensate produced by its interaction with the plasma of inflaton decay products. In these cases we find that estimates for the resulting baryon/lepton asymmetry of the universe are substantially altered. We identify scenarios for the Yukawa couplings to the flat directions, and the order and mass scale of higher-dimensional superpotential interactions that set the initial flat direction vev, that might lead to acceptable baryo/leptogenesis.Comment: 26 pages, 9 Table

Baryogenesis and Late-Decaying Moduli

Late-decaying string moduli dilute the baryon asymmetry of the universe created in any previous era. The reheat temperature for such moduli is below a GeV, thus motivating baryogenesis at very low temperatures. We present an extension of the minimal supersymmetric standard model with TeV-scale colored fields that can yield the correct baryon asymmetry of the universe in this context. Modulus decay, which reheats the universe at a temperature below GeV, produces the visible sector fields and neutralino dark matter in non-thermal fashion. We discuss various possibilities for baryogenesis from TeV scale colored fields and show that they can generate an acceptable baryon asymmetry, while being compatible with phenomenological constraints like neutron-antineutron oscillation.Comment: 8 pages, 3 figure

Gauge invariant MSSM inflaton

We argue that all the necessary ingredients for successful inflation are present in the flat directions of the Minimally Supersymmetric Standard Model. We show that out of many gauge invariant combinations of squarks, sleptons and Higgses, there are two directions, ${\bf LLe}$, and ${\bf udd}$, which are promising candidates for the inflaton. The model predicts more than $10^3$ e-foldings with an inflationary scale of $H_{\rm inf}\sim {\cal O}(1-10)$ GeV, provides a tilted spectrum with an amplitude of $\delta_H\sim 10^{-5}$ and a negligible tensor perturbation. The temperature of the thermalized plasma could be as low as $T_{rh}\sim {\cal O}(1-10)$~TeV. Parts of the inflaton potential can be determined independently of cosmology by future particle physics experiments.Comment: 4 revtex pages, some references added, stabilization of moduli and supergravity effects are discusse

On the complexity of the multiple stack TSP, kSTSP

The multiple Stack Travelling Salesman Problem, STSP, deals with the collect and the deliverance of n commodities in two distinct cities. The two cities are represented by means of two edge-valued graphs (G1,d2) and (G2,d2). During the pick-up tour, the commodities are stored into a container whose rows are subject to LIFO constraints. As a generalisation of standard TSP, the problem obviously is NP-hard; nevertheless, one could wonder about what combinatorial structure of STSP does the most impact its complexity: the arrangement of the commodities into the container, or the tours themselves? The answer is not clear. First, given a pair (T1,T2) of pick-up and delivery tours, it is polynomial to decide whether these tours are or not compatible. Second, for a given arrangement of the commodities into the k rows of the container, the optimum pick-up and delivery tours w.r.t. this arrangement can be computed within a time that is polynomial in n, but exponential in k. Finally, we provide instances on which a tour that is optimum for one of three distances d1, d2 or d1+d2 lead to solutions of STSP that are arbitrarily far to the optimum STSP