258 research outputs found
The nuMSM, leptonic asymmetries, and properties of singlet fermions
We study in detail the mechanism of baryon and lepton asymmetry generation in
the framework of the MSM (an extension of the Standard Model by three
singlet fermions with masses smaller than the electroweak scale). We elucidate
the issue of CP-violation in the model and define the phase relevant for
baryogenesis. We clarify the question of quantum-mechanical coherence,
essential for the lepton asymmetry generation in singlet fermion oscillations
and compute the relevant damping rates. The range of masses and couplings of
singlet leptons which can lead to successful baryogenesis is determined. The
conditions which ensure survival of primordial (existing above the electroweak
temperatures) asymmetries in different leptonic numbers are analysed. We
address the question whether CP-violating reactions with lepton number
non-conservation can produce leptonic asymmetry {\em below} the sphaleron
freeze-out temperature. This asymmetry, if created, leads to resonant
production of dark matter sterile neutrinos. We show that the requirement that
a significant lepton asymmetry be produced puts stringent constraints on the
properties of a pair of nearly degenerate singlet fermions, which can be tested
in accelerator experiments. In this region of parameters the MSM provides
a common mechanism for production of baryonic matter and dark matter in the
universe. We analyse different fine-tunings of the model and discuss possible
symmetries of the MSM Lagrangian that can lead to them.Comment: 56 pages, 16 figures. Many clarifications added, published versio
Gravity, Scale Invariance and the Hierarchy Problem
Combining the quantum scale invariance with the absence of new degrees of
freedom above the electroweak scale leads to stability of the latter against
perturbative quantum corrections. Nevertheless, the hierarchy between the weak
and the Planck scales remains unexplained. We argue that this hierarchy can be
generated by a non-perturbative effect relating the low energy and the
Planck-scale physics. The effect is manifested in the existence of an instanton
configuration contributing to the vacuum expectation value of the Higgs field.
We analyze such configurations in several toy models and in a
phenomenologically viable theory encompassing the Standard Model and General
Relativity in a scale-invariant way. Dynamical gravity and a non-minimal
coupling of it to the Higgs field play a crucial role in the mechanism.Comment: 42 pages, 11 figures. v2: published versio
Why should we care about the top quark Yukawa coupling?
In the cosmological context, for the Standard Model to be valid up to the
scale of inflation, the top quark Yukawa coupling should not exceed the
critical value , coinciding with good precision (about 0.02%) with
the requirement of the stability of the electroweak vacuum. So, the exact
measurements of may give an insight on the possible existence and the
energy scale of new physics above 100 GeV, which is extremely sensitive to
. We overview the most recent theoretical computations of and
the experimental measurements of . Within the theoretical and experimental
uncertainties in the required scale of new physics varies from GeV
to the Planck scale, urging for precise determination of the top quark Yukawa
coupling.Comment: 9 pages, 8 figures. The journal version in JETP special issue. Some
discussion is improved, references added, and (here we reluctantly followed
the editorial request) the abstract is expande
Higgs inflation at the critical point
Higgs inflation can occur if the Standard Model (SM) is a self-consistent
effective field theory up to inflationary scale. This leads to a lower bound on
the Higgs boson mass, . If is more than a few
hundreds of MeV above the critical value, the Higgs inflation predicts the
universal values of inflationary indexes, and ,
independently on the Standard Model parameters. We show that in the vicinity of
the critical point the inflationary indexes acquire an
essential dependence on the mass of the top quark and . In
particular, the amplitude of the gravitational waves can exceed considerably
the universal value.Comment: Improved analysis taking into account one-loop terms in the effective
potential. Sign error in the formula for the running of the spectral index
corrected. Discussion of the relation between the particle physics and
inflationary parameters adde
Higgs-Dilaton cosmology: Universality vs. criticality
The Higgs-Dilaton model is able to produce an early inflationary expansion
followed by a dark energy dominated era responsible for the late time
acceleration of the Universe. At tree level, the model predicts a small
tensor-to-scalar ratio (), a tiny negative running of
the spectral tilt () and a nontrivial
consistency relation between the spectral tilt of scalar perturbations and the
dark energy equation of state, which turns out to be close to a cosmological
constant (). We reconsider the validity of these
predictions in the vicinity of the critical value of the Higgs self-coupling
giving rise to an inflection point in the inflationary potential. The value of
the inflationary observables in this case strongly depends on the parameters of
the model. The tensor-to-scalar ratio can be large [] and
notably exceed its tree-level value. If that happens, the running of the scalar
tilt becomes positive and rather big [] and
the equation-of-state parameter of dark energy can significantly differ from a
cosmological constant [].Comment: 5 pages, 3 figures, published version, added clarifications and
references, corrected typo
Fermion number violating effects in low scale leptogenesis
The existence of baryon asymmetry and dark matter in the Universe may be
related to CP-violating reactions of three heavy neutral leptons (HNLs) with
masses well below the Fermi scale. The dynamical description of the lepton
asymmetry generation, which is the key ingredient of baryogenesis and of dark
matter production, is quite complicated due to the presence of many different
relaxation time scales and the necessity to include quantum-mechanical coherent
effects in HNL oscillations. We derive kinetic equations accounting for fermion
number violating effects missed so far and identify one of the domains of HNL
masses that can potentially lead to large lepton asymmetry generation boosting
the sterile neutrino dark matter production.Comment: 10 pages, 10 figures, Journal version with corrected misprint
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