
Armillis, R., Lazarides, G., & Pallis, C. (2014). Inflation, leptogenesis, and Yukawa quasiunification within a supersymmetric leftright model. Phys. Rev. D, 89(6), 065032–22pp.
Abstract: A simple extension of the minimal leftright symmetric supersymmetric grand unified theory model is constructed by adding two pairs of superfields. This naturally violates the partial Yukawa unification predicted by the minimal model. After including supergravity corrections, we find that this extended model naturally supports hilltop Fterm hybrid inflation along its trivial inflationary path with only a very mild tuning of the initial conditions. With a convenient choice of signs of the terms in the Kahler potential, we can reconcile the inflationary scale with the supersymmetric grand unified theory scale. All the current data on the inflationary observables are readily reproduced. Inflation is followed by nonthermal leptogenesis via the decay of the righthanded neutrinos emerging from the decay of the inflaton, and any possible washout of the lepton asymmetry is avoided thanks to the violation of partial Yukawa unification. The extra superfields also assist us in reducing the reheat temperature so as to satisfy the gravitino constraint. The observed baryon asymmetry of the universe is naturally reproduced consistently with the neutrino oscillation parameters.



Civiletti, M., Pallis, C., & Shafi, Q. (2014). Upper bound on the tensortoscalar ratio in GUTscale supersymmetric hybrid inflation. Phys. Lett. B, 733, 276–282.
Abstract: We explore the upper bound on the tensortoscalar ratio r in supersymmetric (Fterm) hybrid inflation models with the gauge symmetry breaking scale set equal to the value 2.86 . 10(16) GeV, as dictated by the unification of the MSSM gauge couplings. We employ a unique renormalizable superpotential and a quasicanonical Kahler potential, and the scalar spectral index n(s) is required to lie within the twosigma interval from the central value found by the Planck satellite. In a sizable region of the parameter space the potential along the inflationary trajectory is a monotonically increasing function of the inflaton, and for this case, r less than or similar to 2.9.10(4), while the spectral index running, vertical bar dn(s)/d ln k vertical bar, can be as large as 0.01. Ignoring higher order terms which ensure the boundedness of the potential for large values of the inflaton, the upper bound on r is significantly larger, of order 0.01, for subplanckian values of the inflaton, and vertical bar dn(s)/dlnk vertical bar similar or equal to 0.006.



Karagiannakis, N., Lazarides, G., & Pallis, C. (2015). Probing the hyperbolic branch/focus point region of the constrained minimal supersymmetric standard model with generalized Yukawa quasiunification. Phys. Rev. D, 92(8), 085018–15pp.
Abstract: We analyze the parametric space of the constrained minimal supersymmetric standard model with μ> 0 supplemented by a generalized asymptotic Yukawa coupling quasiunification condition which yields acceptable masses for the fermions of the third family. We impose constraints from the cold dark matter abundance in the Universe and its directdetection experiments, the B physics, as well as the masses of the sparticles and the lightest neutral CPeven Higgs boson. Fixing the mass of the latter to its central value from the LHC and taking 40 less than or similar to tan beta less than or similar to 50, we find a relatively wide allowed parameter space with 11 less than or similar to A(0)/M1/2 less than or similar to 15 and a mass of the lightest sparticle in the range (0.091.1) TeV. This sparticle is possibly detectable by the present cold dark matter direct search experiments. The required finetuning for the electroweak symmetry breaking is much milder than the one needed in the neutralinostau coannihilation region of the same model.



Lazaries, G., & Pallis, C. (2015). Shift symmetry and Higgs inflation in supergravity with observable gravitational waves. J. High Energy Phys., 11(11), 114–28pp.
Abstract: We demonstrate how to realize within supergravity a novel chaotictype inflationary scenario driven by the radial parts of a conjugate pair of Higgs superfields causing the spontaneous breaking of a grand unified gauge symmetry at a scale assuming the value of the supersymmetric grand unification scale. The superpotential is uniquely determined at the renormalizable level by the gauge symmetry and a continuous R symmetry. We select two types of Kahler potentials, which respect these symmetries as well as an approximate shift symmetry. In particular, they include in a logarithm a dominant shiftsymmetric term proportional to a parameter c together with a small term violating this symmetry and characterized by a parameter c(+). In both cases, imposing a lower bound on c, inflation can be attained with subplanckian values of the original inflaton, while the corresponding effective theory respects perturbative unitarity for r +/ = c(+)/c_ <= 1. These inflationary models do not lead to overproduction of cosmic defects, are largely independent of the oneloop radiative corrections and accommodate, for natural values of r +/, observable gravitational waves consistently with all the current observational data. The inflaton mass is mostly confined in the range (3.7 – 8.1) x 10(10) GeV.



Pallis, C. (2015). Kinetically modified nonminimal chaotic inflation. Phys. Rev. D, 91(12), 123508–6pp.
Abstract: We consider supersymmetric (SUSY) and nonSUSY models of chaotic inflation based on the phi(n) potential with 2 <= n <= 6. We show that the coexistence of a nonminimal coupling to gravity f(R) = 1 + c(R)phi(n/2) with a kinetic mixing of the form f(K) = c(K)f(R)(m) can accommodate inflationary observables favored by the BICEP2/Keck Array and Planck results for 0 <= m <= 4 and 2.5 x 10(4) <= r(RK) = c(R)/c(K)(n/4) <= 1, where the upper limit is not imposed for n 2. Inflation can be attained for subPlanckian inflaton values with the corresponding effective theories retaining the perturbative unitarity up to the Planck scale.



Pallis, C. (2014). Inducedgravity in inflation noscale supergravity and beyond. J. Cosmol. Astropart. Phys., 08(8), 057–20pp.
Abstract: Supersymmetric versions of inducedgravity inflation are formulated within Supergravity (SUGRA) employing two gauge singlet chiral super fields. The proposed superpotential is uniquely determined by applying a continuous R and a discrete Z(n) symmetry. We select two types of logarithmic Kahler potentials, one associated with a noscaletype SU(2, 1)/SU(2) x U(1)(R) x Z(n) Kahler manifold and one more generic. In both cases, imposing a lower bound on the parameter c R involved in the coupling between the inflaton and the Ricci scalar curvature – e.g. c(R) greater than or similar to 76, 105, 310 for n – 2, 3 and 6 respectively , inflation can be attained even for subplanckian values of the inflaton while the corresponding effective theory respects the perturbative unitarity. In the case of noscale SUGRA we show that, for every n, the inflationary observables remain unchanged and in agreement with the current data while the inflaton mass is predicted to be 3 . 10(13) GeV. Beyond noscale SUGRA the inflationary observables depend mildly on n and crucially on the coefficient involved in the fourth order term of the Kahler potential which mixes the inflaton with the accompanying noninflaton field.



Pallis, C. (2014). Linking Starobinskytype inflation in noscale supergravity to MSSM. J. Cosmol. Astropart. Phys., 04(4), 024–31pp.
Abstract: A novel realization of the Starobinsky inflationary model within a moderate extension of the Minimal Supersymmetric Standard Model (MSSM) is presented. The proposed superpotential is uniquely determined by applying a continuous R and a Z2 discrete symmetry, whereas the Kahler potential is associated with a noscaletype SU(54, 1)/ SU(54) x U(1) R X Z2 Kahler manifold. The inflaton is identified with a Higgslike modulus whose the vacuum expectation value controls the gravitational strength. Thanks to a strong enough coupling (with a parameter CT involved) between the inflaton and the Ricci scalar curvature, inflation can be attained even for subplanckian values of the inflaton with CT >= 76 and the corresponding effective theory being valid up to the Planck scale. The inflationary observables turn out to be in agreement with the current data and the inflaton mass is predicted to be 3 10(3) GeV. At the cost of a relatively small superpotential coupling constant, the model offers also a resolution of the f,t problem of MSSM for CT <= 4500 and gravitino heavier than about 10(4) GeV. Supplementing MSSM by three righthanded neutrinos we show that spontaneously arising couplings between the inflaton and the particle content of MSSM not only ensure a sufficiently low reheating temperature but also support a scenario of nonthermal leptogenesis consistently with the neutrino oscillation parameters.



Pallis, C. (2014). Reconciling inducedgravity inflation in supergravity with the Planck 2013 & BICEP2 results. J. Cosmol. Astropart. Phys., 10(10), 058–18pp.
Abstract: We generalize the embedding of inducedgravity inflation beyond the noscale Supergravity presented in ref. [1] employing two gauge singlet chiral superfields, a superpotential uniquely determined by applying a continuous R and a discrete Z(n) symmetries, and a logarithmic Kahler potential including all the allowed terms up to fourth order in powers of the various fields. We show that, increasing slightly the prefactor (3) encountered in the adopted Kahler potential, an efficient enhancement of the resulting tensortoscalar ratio can be achieved rendering the predictions of the model consistent with the recent BICEP2 results, even with subplanckian excursions of the original inflaton field. The remaining inflationary observables can become compatible with the data by mildly tuning the coefficient involved in the fourth order term of the Kahler potential which mixes the inflaton with the accompanying noninflaton field. The inflaton mass is predicted to be close to 10(14) GeV.



Pallis, C., & Shafi, Q. (2015). Gravity waves from nonminimal quadratic inflation. J. Cosmol. Astropart. Phys., 03(3), 023–31pp.
Abstract: We discuss nonminimal quadratic inflation in supersymmetric (SUSY) and nonSUSY models which entails a linear coupling of the inflaton to gravity. Imposing a lower bound on the parameter c(R), involved in the coupling between the inflaton and the Ricci scalar curvature, inflation can be attained even for subplanckian values of the inflaton while the corresponding effective theory respects the perturbative unitarity up to the Planck scale. Working in the nonSUSY context we also consider radiative corrections to the inflationary potential due to a possible coupling of the inflaton to bosons or fermions. We find ranges of the parameters, depending mildly on the renormalization scale, with adjustable values of the spectral index n(s), tensortoscalar ratio r similar or equal to (2 – 4) . 10(3), and an inflaton mass close to 3 . 10 (13) GeV. In the SUSY framework we employ two gauge singlet chiral superfields, a logarithmic Kahler potential including all the allowed terms up to fourth order in powers of the various fields, and determine uniquely the superpotential by applying a continuous R and a global U(1) symmetry. When the Kahler manifold exhibits a noscaletype symmetry, the model predicts n(s) similar or equal to 0.963 and r similar or equal to 0.004. Beyond noscale SUGRA, n(s) and r depend crucially on the coefficient involved in the fourth order term, which mixes the inflaton with the accompanying noninflaton field in the Kahler potential, and the prefactor encountered in it. Increasing slightly the latter above (3), an efficient enhancement of the resulting r can be achieved putting it in the observable range. The inflaton mass in the last case is confined in the range (5 – 9) . 10(13) GeV.



Pallis, C., & Shafi, Q. (2014). From hybrid to quadratic inflation with highscale supersymmetry breaking. Phys. Lett. B, 736, 261–266.
Abstract: Motivated by the reported discovery of inflationary gravity waves by the BICEP2 experiment, we propose an inflationary scenario in supergravity, based on the standard superpotential used in hybrid inflation. The new model yields a tensortoscalar ratio r similar or equal to 0.14 and scalar spectral index n(s) similar or equal to 0.964, corresponding to quadratic (chaotic) inflation. The important new ingredients are the highscale, (1.610) . 10(13) GeV, soft supersymmetry breaking mass for the gauge singlet inflaton field and a shift symmetry imposed on the Kahler potential. The end of inflation is accompanied, as in the earlier hybrid inflation models, by the breaking of a gauge symmetry at (1.27.1) . 10(16) GeV, comparable to the grandunification scale.

