62 research outputs found
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 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 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 -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 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 -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 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
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
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