511 research outputs found
Effective theories of neutrino masses
The importance of improving the bounds on those effective non-standard neutrino interactions (NSI) which are a signal of all fermionic-mediated Seesaws is stressed: they are revealed as non-unitarity of the leptonic mixing matrix, and at experimental reach for seesaw scales ≤ O(TeV). Some recent activity in the literature on other -theoretically not well motivated- ill-constrained NSI are also summarized. Furthermore, the status of the simplest Seesaw scenario with only two heavy neutrinos is reviewed. This model happens to be a explicit realization of the effective Minimal Flavour Violation approach. We derive the scalar potential for the fields whose background values are the Yukawa couplings of that model, and explore its minima. The Majorana character plays a distinctive role: the minimum of the potential allows for large mixing angles -in contrast to the simplest quark case- and predicts a maximal Majorana phase. This points in turn to a strong correlation between neutrino mass hierarchy and mixing patter
Standard Model Baryogenesis
Simply on CP arguments, we argue against a Standard Model explanation of
baryogenesis via the charge transport mechanism. A CP-asymmetry is found in the
reflection coefficients of quarks hitting the electroweak phase boundary
created during a first order phase transition. The problem is analyzed both in
an academic zero temperature case and in the realistic finite temperature one.
At finite temperature, a crucial role is played by the damping rate of
quasi-quarks in a hot plasma, which induces loss of spatial coherence and
suppresses reflection on the boundary even at tree-level. The resulting baryon
asymmetry is many orders of magnitude below what observation requires. We
comment as well on related works.Comment: 10 pages, CERN-TH. 7368/94, LPTHE Orsay-94/71, HD-THEP-94-2
On the Potential of Leptonic Minimal Flavour Violation
Minimal Flavour Violation can be realized in several ways in the lepton
sector due to the possibility of Majorana neutrino mass terms. We derive the
scalar potential for the fields whose background values are the Yukawa
couplings, for the simplest See-Saw model with just two right-handed neutrinos,
and explore its minima. The Majorana character plays a distinctive role: the
minimum of the potential allows for large mixing angles -in contrast to the
simplest quark case- and predicts a maximal Majorana phase. This points in turn
to a strong correlation between neutrino mass hierarchy and mixing pattern.Comment: 6 pages; version published on Physics Letters
Analysis of General Power Counting Rules in Effective Field Theory
We derive the general counting rules for a quantum effective field theory
(EFT) in dimensions. The rules are valid for strongly and weakly
coupled theories, and predict that all kinetic energy terms are canonically
normalized. They determine the energy dependence of scattering cross sections
in the range of validity of the EFT expansion. We show that the size of cross
sections is controlled by the power counting of EFT, not by chiral
counting, even for chiral perturbation theory (PT). The relation between
and is generalized to dimensions. We show that the
naive dimensional analysis counting is related to counting. The
EFT counting rules are applied to PT, low-energy weak interactions,
Standard Model EFT and the non-trivial case of Higgs EFT.Comment: V2: more details and examples added; version published in journal. 17
pages, 4 figures, 2 table
On the renormalization of the electroweak chiral Lagrangian with a Higgs
We consider the scalar sector of the effective non-linear electroweak
Lagrangian with a light "Higgs" particle, up to four derivatives in the chiral
expansion. The complete off-shell renormalization procedure is implemented,
including one loop corrections stemming from the leading two-derivative terms,
for finite Higgs mass. This determines the complete set of independent chiral
invariant scalar counterterms required for consistency; these include bosonic
operators often disregarded. Furthermore, new counterterms involving the Higgs
particle which are apparently chiral non-invariant are identified in the
perturbative analysis. A novel general parametrization of the pseudoescalar
field redefinitions is proposed, which reduces to the various usual ones for
specific values of its parameter; the non-local field redefinitions reabsorbing
all chiral non-invariant counterterms are then explicitly determined. The
physical results translate into renormalization group equations which may be
useful when comparing future Higgs data at different energies
Large gauge invariant non-standard neutrino interactions
Theories beyond the Standard Model must necessarily respect its gauge
symmetry. This implies strict constraints on the possible models of
non-standard neutrino interactions, which we analyze. The focus is set on the
effective low-energy dimension six and eight operators involving four leptons,
decomposing them according to all possible tree-level mediators, as a guide for
model building. The new couplings are required to have sizeable strength, while
processes involving four charged leptons are required to be suppressed. For
non-standard interactions in matter, only diagonal tau-neutrino interactions
can escape these requirements and can be allowed to result from dimension six
operators. Large non-standard neutrino interactions from dimension eight
operators alone are phenomenologically allowed in all flavour channels and
shown to require at least two new mediator particles. The new couplings must
obey general cancellation conditions both at the dimension six and eight
levels, which result from expressing the operators obtained from the mediator
analysis in terms of a complete basis of operators. We illustrate with one
example how to apply this information to model building.Comment: 34 pages, 4 figures, 5 tables. Final version in PR
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