Affleck-Dine leptogenesis via multiple flat directions

A pseudo Nambu-Goldstone boson as curvaton avoids the eta-problem of inflation which plagues most curvaton candidates. We point out that a concrete realization of the curvaton mechanism with a pseudo Nambu-Goldstone boson can be found in the supersymmetric Peccei-Quinn mechanism resolving the strong CP problem. In the flaton models of Peccei-Quinn symmetry breaking, the angular degree of freedom associated with the QCD axion can naturally be a flat direction during inflation and provides successful curvature perturbations. In this scheme, the preferred values of the axion scale and the Hubble parameter during inflation turn out to be about 10^{10} GeV and 10^{12} GeV, respectively. Moreover, it is found that a significant isocurvature component, (anti)correlated to the overall curvature perturbation, can be generated, which is a smoking-gun for the curvaton scenario. Finally, non-Gaussianity in the perturbation spectrum at potentially observable level is also possible.

We discuss a spontaneous baryogenesis mechanism in flat directions. After identifying the Nambu-Goldstone mode which derivatively couples to the associated $U(1)$ current and rotates due to the A term, we show that spontaneous baryogenesis can be naturally realized in the context of the flat direction. As applications, we discuss two scenarios of baryogenesis in detail. One is baryogenesis in a flat direction with a vanishing $B\ensuremath{-}L$ charge, especially with neither baryon nor lepton charge, which was recently proposed by Chiba and the present authors. The other is a baryogenesis scenario compatible with a large lepton asymmetry.

Flat directions in the minimal supersymmetric standard model are known to deform into non-topological solitons, Q-balls, which generally possess both baryon and lepton asymmetries. We investigate how Q-balls evolve if some of the constituent fields of the flat direction decay into light species. It is found that the Q-balls takes a new configuration whose energy per charge slightly increases due to the decay. Specifically, we show that all the stable Q-balls eventually transform into pure B-balls via the decay into neutrinos.

Recent developments in string theory have led to ``realistic string compactifications which lead to moduli stabilization while generating a hierarchy between the Electroweak and Planck scales at the same time. However, this seems to suggest a rethink of our standard notions of cosmological evolution after the end of inflation and before the beginning of BBN. This epoch is crucial for addressing the issues of neutrino masses, baryon asymmetry, Dark Matter (DM) abundance and the moduli (gravitino) problem. We argue that within classes of realistic string compactifications as defined above, there generically exists a light modulus with a mass comparable to that of the gravitino which is typically much smaller than the Hubble parameter during inflation. Therefore, it is destabilized and generates a large late-time entropy when it decays. Thus, all known elegant mechanisms of generating the baryon asymmetry of the Universe in the literature have to take this fact into account. In this work, we find that it is still possible to naturally generate the observed baryon asymmetry of the Universe as well as light left-handed neutrino masses from a period of Affleck-Dine (AD) leptogenesis shortly after the end of inflation, in classes of realistic string constructions with a minimal extension of the MSSM below the unification scale (consisting only of right-handed neutrinos) and satisfying certain microscopic criteria described in the text. The AD mechanism has already been used to generate the baryon asymmetry in the literature; however in this work we have embedded the above mechanism within a framework well motivated from string theory and have tried to describe the epoch from the end of inflation to the beginning of BBN in a complete and self-consistent manner. The consequences of our analysis are as follows. The lightest left-handed neutrino is required to be virtually massless. The moduli (gravitino) problem can be naturally solved in this framework both within gravity and gauge mediation. The observed upper bound on the relic abundance constrains the moduli-matter and moduli-gravitino couplings since the DM is produced non-thermally within this framework. Finally, although not a definite prediction, the framework naturally allows a light right-handed neutrino and sneutrinos around the electroweak scale which could have important implications for the nature of DM as well as the LHC.

We study a No-Scale supergravity inflation model which has a non-minimal deformation of the Kähler potential and a Wess-Zumino superpotential extended by the inclusion of a Polonyi mass term. The non-minimal structure of the Kähler potential is responsible for an inflexion point that can lead to the production of gravitational waves at late stages of inflation, while the Polonyi term breaks supersymmetry at the end of inflation, generating a non-vanishing gravitino mass. After a thorough parameter space scan, we identify promising points for gravitational wave production. We then study the resulting gravitational wave energy density for this set of points, and we observe that the gravitational waves should be observable in the next generation of both space-based and ground-based interferometers. Finally, we show how the presence of the Polonyi term can be used to further boost the gravitational wave energy density, which is correlated with the gravitino mass. The code used for the scan and the numerical analysis is provided at https://gitlab.com/miguel.romao/gw-and-m32-no-scale-inflation-polonyi.

We investigate the role of leptons in electroweak baryogenesis by studying a relatively simple framework inspired by effective field theory that satisfies all Sakharov conditions. In particular, we study the effectiveness of CP-violating source terms induced by dimension-six Yukawa interactions for quarks and charged leptons. Despite the relatively small Yukawa coupling, CP-violating source terms involving taus are quite effective and can account for the observed matter-antimatter asymmetry. We obtain analytical and numerical expressions for the total baryon asymmetry, the former providing important insight into what makes lepton CP violation relatively effective compared to quark CP violation. Leptons also play an important role if the CP-violating source involves top quarks. While the tau Yukawa coupling in the Standard Model is small, it significantly enhances the baryon asymmetry by transferring the chiral asymmetry in quarks, which is washed out by strong sphalerons, to a chiral asymmetry in leptons. We conclude that leptons should not be ignored even if CP violation is limited to the quark sector. The role of leptons can be further increased in scenarios of new physics with additional chiral-symmetry-breaking interactions between quarks and leptons, as can happen in models with additional Higgs bosons or leptoquarks. Finally, we study CP-violating dimension-six Yukawa interactions for lighter quarks and leptons but conclude that these lead to too small baryon asymmetries.

Neutrino degeneracy effect on neutrino oscillations and primordial helium yield

We investigate the dynamics of inflation models driven by multiple, decoupled scalar fields and calculate the Hubble parameter and the amplitude of the lightest field at the end of inflation. The results are very simple and similar to those of the single field inflation, mainly depending on the underlying spectrum of the masses. The mass distribution is heavily constrained by the power spectrum of density perturbations P and the spectral index ns. The overall mass scale gives the amplitude of P and ns is affected by the number of fields and the spacing between masses in the distribution. The drop‐out effect of the massive fields makes the perturbation spectrum typically redder than the single field inflation spectrum. We illustrate this using two different mass distributions.

In this paper, we investigate a scenario of variable gravity and apply it to\nthe unified description of inflation and late time cosmic acceleration dubbed\nquintessential inflation. The scalar field called "cosmon" which in this model\nunifies both the concepts reduces to inflaton at early epochs. We calculate the\nslow-roll parameters, the Hubble parameter at the end of inflation, the\nreheating temperature,the tensor-to-scalar ration and demonstrate the agreement\nof the model with observations and the Planck data.As for the post inflationary\ndynamics, cosmon tracks the background before it exits the scaling regime at\nlate times. The scenario gives rise to correct epoch sequence of standard\ncosmology, namely, radiative regime, matter phase and dark-energy. We show that\nthe long kinetic regime after inflation gives rise to enhancement of relic\ngravity wave amplitude resulting into violation of nucleosynthesis constraint\nat the commencement of radiative regime in case of an inefficient reheating\nmechanism such as gravitational particle production. Instant preheating is\nimplemented to successfully circumvent the problem. As a generic feature, the\nscenario gives rise to a blue spectrum for gravity waves on scales smaller than\nthe comoving horizon scale at the commencement of the radiative regime.\n

In this work, we develop a generic formalism for the study of cosmological tensor perturbations induced at second order by first-order vector metric perturbations, dubbing these induced tensor modes vector-induced gravitational waves (VIGWs). In the presence of an active source such as primordial magnetic fields (PMFs), the vector perturbations of the metric do not necessarily decay rapidly with Hubble expansion, but may remain significantly large in amplitude depending upon the background equation-of-state (EoS) parameter, w, during reheating. Considering an inflation-inspired PMF power spectrum of the power-law form PB (k) ∝ k n B (where n B is the magnetic spectral index), we show that the VIGW signal is enhanced for a stiff post-inflationary EoS, with the maximum enhancement happening for w = 1 (kination). The VIGW spectrum exhibits a maximum around the scale crossing the cosmological horizon at the end of reheating, k reh, while its present day peak amplitude scales as ΩGW(k reh,η 0) ∝ [10ΔN reh (H inf/M Pl)]8, where H inf is the Hubble parameter at the end of inflation and ΔN reh is the duration of the post-inflationary era in e-folds. For w = 1 and n B > -3/2, one further obtains a nearly n B-independent frequency scaling of the GW spectrum of the form ΩGW(f,η 0) ∝ (f/f reh)-2.8 for f > f reh ≡ k reh/(2π). We also explicitly demonstrate that the VIGW spectrum is dominant over that of the first-order magnetically-sourced GWs from the reheating era. Finally, it is highlighted that the VIGW signal may lie well within the detection bands of several next-generation interferometric GW missions at small scales. Indicatively, for H inf ∼ O(107) GeV and O(1014) GeV, and ΔN reh ∼ 15 and 10, the VIGW signal is found to be detectable by LISA and ET respectively.

We study a scale-invariant model of quadratic gravity with a non-minimally coupled scalar field. We focus on cosmological solutions and find that scale invariance is spontaneously broken and a mass scale naturally emerges. Before the symmetry breaking, the Universe undergoes an inflationary expansion with nearly the same observational predictions of Starobinsky's model. At the end of inflation, the Hubble parameter and the scalar field converge to a stable fixed point through damped oscillations and the usual Einstein-Hilbert action is recovered. The oscillations around the fixed point can reheat the Universe in various ways and we study in detail some of these possibilities.

We discuss the constraints on the inhomogeneous reheatingscenario. In particular, we discuss the prospects for low scaleinflation with a Hubble constant of the order of the gravitinomass, and the possibility that an MSSM flat direction isresponsible for the density fluctuations. Thermal effects aregenerically fatal for the scenario, and can only be avoided forsmall enough mass and couplings of the flat direction field,excluding MSSM flat directions. Prompt decay at the end ofinflation bypasses thermal constraints, and is compatible withboth low scale inflation and MSSM flat directions. However, thelevel of non-Gaussianity is acceptably small only for a smallwindow of inflaton mass and couplings. The upshot is thattuning of parameters is needed for the inhomogeneous reheatingscenario to work.

We investigate the production of dark matter from metric perturbations produced during inflation or in standard cosmology. Perturbations break Weyl flatness of the Friedmann-Lemaître-Robertson-Walker metric, allowing conformally coupled fields-in particular, fermions studied here-to be produced even when their mass is negligible. Particle production can be computed by studying the Bogoliubov transformation induced by the stochastic background. For perturbations generated during inflation, we present a closed formula for the resulting abundance of particles that depends solely on the power spectrum of curvature perturbations at the end of inflation. This production mechanism can be dominant especially if the amplitude of curvature perturbations is enhanced for modes that exit the horizon toward the end of inflation. In the simplest scenario, the critical dark matter abundance is reproduced for M≳10^{6} GeV.

We introduce a frame-covariant formalism for inflation of scalar-curvature theories by adopting a differential geometric approach which treats the scalar fields as coordinates living on a field-space manifold. This ensures that our description of inflation is both conformally and reparameterization covariant. Our formulation gives rise to extensions of the usual Hubble and potential slow-roll parameters to generalized fully frame-covariant forms, which allow us to provide manifestly frame-invariant predictions for cosmological observables, such as the tensor-to-scalar ratio r, the spectral indices nR and nT, their runnings αR and αT, the non-Gaussianity parameter fNL, and the isocurvature fraction βiso. We examine the role of the field space curvature in the generation and transfer of isocurvature modes, and we investigate the effect of boundary conditions for the scalar fields at the end of inflation on the observable inflationary quantities. We explore the stability of the trajectories with respect to the boundary conditions by using a suitable sensitivity parameter. To illustrate our approach, we first analyze a simple minimal two-field scenario before studying a more realistic nonminimal model inspired by Higgs inflation. We find that isocurvature effects are greatly enhanced in the latter scenario and must be taken into account for certain values in the parameter space such that the model is properly normalized to the observed scalar power spectrum PR. Finally, we outline how our frame-covariant approach may be extended beyond the tree-level approximation through the Vilkovisky–De Witt formalism, which we generalize to take into account conformal transformations, thereby leading to a fully frame-invariant effective action at the one-loop level.

The observation of neutrino masses leads to the possibility of leptonic mixing and CP violation. One of the simplest extensions of the Standard Model giving rise to neutrino masses consists of the introduction of one righthanded neutrino field per generation, singlet of SU(2). In the context of the seesaw mechanism this leads to three light and three heavy neutrinos. The charged current interactions couple the charged leptons to both the light and the heavy physical neutrinos and leptonic CP violation may occur at low energies as well as at high energies giving rise to the possibility of leptogenesis. There are special scenarios where it is possible to establish a connection between CP violation at the two different scales, an interesting example is included in this work. Furthermore, we describe how the conjecture that all phenomena of CP violation present in nature could have a common origin can be realized in the framework of a further minimal extension of the Standard Model with CP broken through the phase of the vacuum expectation value of a complex Higgs singlet.