Combining Experimental and Cosmological Constraints on Heavy Neutrinos

We study experimental and cosmological constraints on the extension of the Standard Model by three right handed neutrinos with masses between those of the pion and W boson. We combine for the first time direct, indirect and cosmological constraints in this mass range. This includes experimental constraints from neutrino oscillation data, neutrinoless double $\beta$ decay, electroweak precision data, lepton universality, searches for rare lepton decays, tests of CKM unitarity and past direct searches at colliders or fixed target experiments. On the cosmological side, big bang nucleosynthesis has the most pronounced impact. Our results can be used to evaluate the discovery potential of searches for heavy neutrinos at LHCb, BELLE II, SHiP, ATLAS, CMS or a future lepton collider.Comment: 64 pages, 22 figures. Matches published versio

Slow Roll during the Waterfall Regime: The Small Coupling Window for SUSY Hybrid Inflation

It has recently been pointed out that a substantial amount of e-folds can occur during the waterfall regime of hybrid inflation. Moreover, Kodama et.al. have derived analytic approximations for the trajectories of the inflaton and of the waterfall fields. Based on these, we derive here the consequences for F- and D-term SUSY hybrid inflation: A substantial amount of e-folds may occur in the waterfall regime, provided kappa << M^2/M_P^2, where kappa is the superpotential coupling, M the scale of symmetry breaking and M_P the reduced Planck mass. When this condition is amply fulfilled, a number of e-folds much larger than N_e\approx60 can occur in the waterfall regime and the scalar spectral index is then given by the expression found by Kodama et.al. n_s=1-4/N_e. This value may be increased up to unity, if only about N_e e-folds occur during the waterfall regime, such that the largest observable scale leaves the horizon close to the critical point of hybrid inflation, what can be achieved for kappa\approx10^(-13) and M\approx5x10^(12) GeV in F-term inflation. Imposing the normalization of the power spectrum leads to a lower bound on the scale of symmetry breaking.Comment: 14 pages, 4 figures, minor corrections, references added, accepted for publication in Phys.Rev.

Leptogenesis from Additional Higgs Doublets

Leptogenesis may be induced by the mixing of extra Higgs doublets with experimentally accessible masses. This mechanism relies on diagrammatic cuts that are kinematically forbidden in the vacuum but contribute at finite temperature. A resonant enhancement of the asymmetry occurs generically provided the dimensionless Yukawa and self-interactions are suppressed compared to those of the Standard Model Higgs field. This is in contrast to typical scenarios of Resonant Leptogenesis, where the asymmetry is enhanced by imposing a degeneracy of singlet neutrino masses.Comment: 12 pages; more phenomenological details adde

Probing leptogenesis with GeV-scale sterile neutrinos at LHCb and BELLE II

We show that existing laboratory experiments have the potential to unveil the origin of matter by probing leptogenesis in the type-I seesaw model with three right-handed neutrinos and Majorana masses in the GeV range. The baryon asymmetry is generated by CP-violating flavour oscillations during the production of the right-handed neutrinos. In contrast to the case with only two right-handed neutrinos, no degeneracy in the Majorana masses is required. The right-handed neutrinos can be found in meson decays at BELLE II and LHCb.Comment: Title changed, discussion extended and references added. 12 pages, one figur

Relativistic and spectator effects in leptogenesis with heavy sterile neutrinos

For leptogenesis with heavy sterile neutrinos above the electroweak scale, asymmetries produced at early times (in the relativistic regime) are relevant, if they are protected from washout. This can occur for weak washout or when the asymmetry is partly protected by being transferred to spectator fields. We thus study the relevance of relativistic effects for leptogenesis in a minimal seesaw model with two sterile neutrinos in the strongly hierarchical limit. Starting from first principles, we derive a set of momentum-averaged fluid equations to calculate the final $B-L$ asymmetry as a function of the washout strength and for different initial conditions at order one accuracy. For this, we take the leading fluid approximation for the relativistic $CP$-even and odd rates. Assuming that spectator fields remain in chemical equilibrium, we find that for weak washout, relativistic corrections lead to a sign flip and an enhancement of the asymmetry for a vanishing initial abundance of sterile neutrinos. As an example for the effect of partially equilibrated spectators, we consider bottom-Yukawa and weak-sphaleron interactions in leptogenesis driven by sterile neutrinos with masses $\gtrsim 5\times10^{12}$ GeV. For a vanishing initial abundance of sterile neutrinos, this can give rise to another flip and an absolute enhancement of the final asymmetry in the strong washout regime by up to two orders of magnitude relative to the cases either without spectators or with fully equilibrated ones. These effects are less pronounced for thermal initial conditions for the sterile neutrinos. The $CP$-violating source in the relativistic regime at early times is important as it is proportional to the product of lepton-number violating and lepton-number conserving rates, and therefore less suppressed than an extrapolation of the nonrelativistic approximations may suggest.Comment: 47 pages, 11 figure

Non-Gaussianities and Curvature Perturbations from Hybrid Inflation

For the original hybrid inflation as well as the supersymmetric F-term and D-term hybrid models, we calculate the level of non-gaussianities and the power spectrum of curvature perturbations generated during the waterfall, taking into account the contribution of entropic modes. We focus on the regime of mild waterfall, in which inflation continues for more than about 60 e-folds N during the waterfall. We find that the associated f_nl parameter goes typically from f_nl \simeq -1 / N_exit in the regime with N >> 60, where N_exit is the number of e-folds between the time of Hubble exit of a pivot scale and the end of inflation, down to f_nl ~-0.3 when N \gtrsim 60, i.e. much smaller in magnitude than the current bound from Planck. Considering only the adiabatic perturbations, the power spectrum is red, with a spectral index n_s = 1 - 4 / N_exit, in the case N >> 60, whereas in the case N \gtrsim 60, it increases up to unity. Including the contribution of entropic modes does not change the observable predictions in the first case. However, in the second case, they are a relevant source for the power spectrum of curvature perturbations, of which the amplitude increases by several orders of magnitudes and can lead to black hole formation. We conclude that due to the important contribution of entropic modes, the parameter space leading to a mild waterfall phase is excluded by CMB observations for all the considered models.Comment: 17 pages, 5 figures, Phys.Rev.D versio

Hybrid Inflation Exit through Tunneling

For hybrid inflationary potentials, we derive the tunneling rate from field configurations along the flat direction towards the waterfall regime. This process competes with the classically rolling evolution of the scalar fields and needs to be strongly subdominant for phenomenologically viable models. Tunneling may exclude models with a mass scale below 10^12 GeV, but can be suppressed by small values of the coupling constants. We find that tunneling is negligible for those models, which do not require fine tuning in order to cancel radiative corrections, in particular for GUT-scale SUSY inflation. In contrast, electroweak scale hybrid inflation is not viable, unless the inflaton-waterfall field coupling is smaller than approximately 10^-11.Comment: 17 pages, 2 figure

Some Aspects of Inflationary Particle Production

Particle production by a varying mass term and by the background metric are considered. We derive a definition of particle number in kinetic theory for both, fermionic and scalar case, which we generalize to the situation of a flavour-mixing mass matrix. This allows us to endow the process of preheating with C and CP violation, leading to the coherent baryogenesis scenario. We present models where this mechanism is operative in the context of hybrid inflation and the grand unified theories Pati-Salam and SO(10). It is shown that a baryon asymmetry in accordance with observation may result. Moreover, we consider issues of quantum theory in curved space. Scalar fields in the expanding Universe and in Rindler space are discussed. It turns out that besides the particle detection rate, the Lamb shift of energy levels is an important effect experienced by Unruh's detector in these spacetimes

Quantum Corrections to the Reissner-Nordstr\"{o}m and Kerr-Newman Metrics

We use effective field theory techniques to examine the quantum corrections to the gravitational metrics of charged particles, with and without spin. In momentum space the masslessness of the photon implies the presence of nonanalytic pieces $\sim \sqrt{-q^2},q^2\log -q^2$ etc. in the form factors of the energy-momentum tensor. We show how the former reproduces the classical non-linear terms of the Reissner-Nordstr\"{o}m and Kerr-Newman metrics while the latter can be interpreted as quantum corrections to these metrics, of order $G\alpha\hbar/mr^3$Comment: 16 page latex file with two figure

Perturbative and Nonperturbative Contributions to a Simple Model for Baryogenesis

Single field baryogenesis, a scenario for Dirac leptogenesis sourced by a time-dependent scalar condensate, is studied. We compare the creation of the charge asymmetry by the perturbative decay of the condensate with the nonperturbative decay, a process of particle production commonly known in the context of inflation as preheating. The nonperturbative channel dominates when the coupling of the scalar field to leptons is sufficiently large.Comment: 11 pages, 3 figure