517 research outputs found
Scattering processes could distinguish Majorana from Dirac neutrinos
It is well known that Majorana neutrinos have a pure axial neutral current
interaction while Dirac neutrinos have the standard vector-axial interaction.
In spite of this crucial difference, usually Dirac neutrino processes differ
from Majorana processes by a term proportional to the neutrino mass, resulting
in almost unmeasurable observations of this difference. In the present work we
show that once the neutrino polarization evolution is considered, there are
clear differences between Dirac and Majorana scattering on electrons. The
change of polarization can be achieved in astrophysical environments with
strong magnetic fields. Furthermore, we show that in the case of unpolarized
neutrino scattering onto polarized electrons, this difference can be relevant
even for large values of the neutrino energy.Comment: 12 pages, 5 figure
Supersymmetric contribution to B to rho K and B to pi K^* decays in SCET
We analyze the supersymmetric contributions to the direct CP asymmetries of
the decays and within Soft Collinear Effective
Theory. We extend the Standard Model analysis of these asymmetries to include
the next leading order QCD corrections. We find that, even with QCD correction,
the Standard Model predictions can not accommodate the direct CP asymmetries in
these decay modes. Using Mass Insertion Approach, we show that non-minimal
flavor SUSY contributions mediated by gluino exchange can enhance the CP
asymmetries significantly and thus can accommodate the experimental results.Comment: 12 pages, 5 figures, version to appear in PL
Dynamical Symmetry Breaking With a Fourth Generation
Adding a fourth generation to the Standard Model and assuming it to be valid
up to some cutoff \Lambda, we show that electroweak symmetry is broken by
radiative corrections due to the fourth generation. The effects of the fourth
generation are isolated using a Lagrangian with a genuine scalar without
self-interactions at the classical level. For masses of the fourth generation
consistent with electroweak precision data (including the B \rightarrow K \pi\
CP asymmetries) we obtain a Higgs mass of the order of a few hundreds GeV and a
cutoff \Lambda\ around 1-2 TeV. We study the reliability of the perturbative
treatment used to obtain these results taking into account the running of the
Yukawa couplings of the fourth quark generation with the aid of the
Renormalization Group (RG) equations, finding similar allowed values for the
Higgs mass but a slightly lower cut-off due to the breaking of the perturbative
regime. Such low cut-off means that the effects of new physics needed to
describe electroweak interactions at energy above \Lambda\ should be measurable
at the LHC. We use the minimal supersymmetric extension of the standard model
with four generations as an explicit example of models realizing the dynamical
electroweak symmetry breaking by radiative corrections and containing new
physics. Here, the cutoff is replaced by the masses of the squarks and
electroweak symmetry breaking by radiative corrections requires the squark
masses to be of the order of 1 TeV.Comment: 20 pages, 7 figures. New section adde
Is the standard Higgs scalar elementary?
In the standard electroweak model, the measured top quark mass requires a
sizeable Yukawa coupling to the fundamental scalar. This large coupling alone
might induce a dynamical breaking of the electroweak symmetry as well as
non-perturbative effects. If such is the case, even a standard Higgs scalar as
light as 80 GeV should have a non-negligible component induced by
the top condensate.Comment: 8 pages, Latex fil
Neutrino Spin Flavor Precession and Leptogenesis
We argue that \Delta L=2 neutrino spin flavor precession, induced by the
primordial magnetic fields, could have a significant impact on the leptogenesis
process that accounts for the baryon asymmetry of the universe. Although the
extra galactic magnetic fields is extremely weak at present time (about 10^{-9}
Gauss), the primordial magnetic filed at the electroweak scale could be quite
strong (of order 10^{17} Gauss). Therefore, at this scale, the effects of the
spin flavor precession are not negligible. We show that the lepton asymmetry
may be reduced by 50% due to the spin flavor precession. In addition, the
leptogenesis will have different feature from the standard scenario of
leptogenesis, where the lepton asymmetry continues to oscillate even after the
electroweak phase transition.Comment: 5 pages, one figure. References adde
Annihilation contribution and decays
We analyze the decays and
and show that within the factorization approximation a phenomenological
consistent picture can be obtained. We show that in this approach the
operator provides the dominant contributions to the suppressed channel . When the is considered a two quark state, evaluation of the
annihilation form factor using Perturbative implies that this
contribution is not negligible, and furthermore it can interfere constructively
or destructively with other penguin contributions. As a consequence of this
ambiguity, the positive identification of can not
distinguish between the two or four quark assignment of the . According to
our calculation, a best candidate to distinguish the nature of scalar is
since the predictions for a four quark model is one
order of magnitude smaller than for the two quark assignment. When the scalars
are seen as two quarks states, simple theoretical assumptions based on SU(2)
isospin symmetry provide relations between different B decays involving one
scalar and one pseudoscalar meson.Comment: 12 pages, 3 figure
XXZ spin chain in transverse field as a regularization of the sine-Gordon model
We consider here XXZ spin chain perturbed by the operator sigma^x (``in
transverse field'') which is a lattice regularization of the sine-Gordon model.
This can be shown using conformal perturbation theory. We calculated mass
ratios of particles which lie in a discrete part of the spectrum and obtained
results in accord with the DHN formula and in disagreement with recent
calculations in literature based on numerical Bethe Ansatz and infinite
momentum frame methods. We also analysed a short distance behavior of this
states (UV or conformal limit). Our result for conformal dimension of the
second breather state is different from the conjecture in [Klassen and Melzer,
Int. J. Mod. Phys. A8, 4131 (1993)] and is consistent with this paper for other
states.Comment: 7 pages, REVTeX, 6 figures, to appear in Phys. Rev.
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