178 research outputs found
Probing seesaw at LHC
We have recently proposed a simple SU(5) theory with an adjoint fermionic
multiplet on top of the usual minimal spectrum. This leads to the hybrid
scenario of both type I and type III seesaw and it predicts the existence of
the fermionic SU(2) triplet between 100 GeV and 1 TeV for a conventional GUT
scale of about 10^{16} GeV, with main decays into W (Z) and leptons, correlated
through Dirac Yukawa couplings, and lifetimes shorter than about 10^{-12} sec.
These decays are lepton number violating and they offer an exciting signature
of Delta L=2 dilepton events together with 4 jets at future pp (p\bar p)
colliders. Increasing the triplet mass endangers the proton stability and so
the seesaw mechanism could be directly testable at LHC.Comment: 19 pages, discussion on leptogenesis added, new references, main
conclusions unchange
Yukawa sector in non-supersymmetric renormalizable SO(10)
We discuss the ordinary, non-supersymmetric SO(10) as a theory of fermion
masses and mixings. We construct two minimal versions of the Yukawa sector
based on and either or . The latter case is of
particular interest since it connects the absolute neutrino mass scale with the
size of the atmospheric mixing angle . It also relates the smallness
of with the largeness of . These results are based on the
analytic study of the second and third generations. Furthermore, we discuss the
structure of the light Higgs and the role of the Peccei-Quinn symmetry for dark
matter and the predictivity of the theory.Comment: 8 pages. Reference added, one formula correcte
Type II Seesaw at LHC: the Roadmap
In this Letter we revisit the type-II seesaw mechanism based on the addition
of a weak triplet scalar to the standard model. We perform a comprehensive
study of its phenomenology at the LHC energies, complete with the electroweak
precision constraints. We pay special attention to the doubly-charged
component, object of collider searches for a long time, and show how the
experimental bound on its mass depends crucially on the particle spectrum of
the theory. Our study can be used as a roadmap for future complete LHC studies.Comment: 5 pages, 4 figures; added discussion on collider signatures including
the impact on SM Higgs searches and accommodating Higgs to two photon rate,
and references; latest version agrees with the published on
Type II see-saw dominance in SO(10)
Grand unified theories where the neutrino mass is given by Type II seesaw
have the potential to provide interesting connections between the neutrino and
charged fermion sectors. We explore the possibility of having a dominant Type
II seesaw contribution in supersymmetric SO(10). We show that this can be
achieved in the model where symmetry breaking is triggered by 54 and
45-dimensional representations, without the need for additional fields other
than those already required to have a realistic charged fermion mass spectrum.
Physical consequences, such as the implementation of the BSV mechanism, the
possibility of the fields responsible for Type II see-saw dominance being
messengers of supersymmetry breaking, and the realization of baryo and
leptogenesis in this theories are discussed.Comment: 14 pages, 3 figures. New version with references adde
Spontaneous CP violation and the B system
We investigate effects of spontaneous breakdown of CP in
systems in left-right symmetric models.
Assuming that the left-right contribution to the matrix
element can be at most equal to the standard model one we obtain a new
lower bound, M_H\gsim 12 TeV, on the flavour changing Higgs boson mass. Most
importantly, the convention independent parameter
which measures the amount of CP violation, can be enhanced by a
factor of four or more for and almost by two orders of magnitude for
systems when compared with the Standard Model predictions. Therefore,
interesting possibilities to observe indirect CP violation in the system
are open in the planned facilities.Comment: 19 pages, LATEX, 4 postscript figures include
Minimal Supersymmetric Pati-Salam Theory: Determination of Physical Scales
We systematically study the minimal supersymmetric Pati-Salam theory, paying
special attention to the unification constraints. We find that the SU(4)_c
scale M_c and the Left-Right scale M_R lie in the range 10^{10} GeV < M_c <
10^{14} GeV, 10^{3} GeV < M_R <10^{10} GeV (with single-step breaking at
10^{10} GeV), giving a potentially accessible scale of parity breaking. The
theory includes the possibility of having doubly-charged supermultiplets at the
supersymmetry breaking scale; color octet states with mass of order M_R^2/M_c;
magnetic monopoles of intermediate mass that do not conflict with cosmology,
and a 'clean' (type I) form for the see-saw mechanism of neutrino mass.Comment: 5 page
Radiative seesaw and degenerate neutrinos
The radiative see-saw mechanism of Witten generates the right-handed neutrino
masses in SO(10) with the spinorial 16_H Higgs field. We study here
analytically the 2nd and 3rd generations for the minimal Yukawa structure
containing 10_H and 120_H Higgs representations. In the approximation of small
2nd generation masses and gauge loop domination we find the following results :
(1) b-tau unification, (2) natural coexistence between large theta_l and small
theta_q, (3) degenerate neutrinos.Comment: 4 page
Neutrino Masses and the LHC: Testing Type II Seesaw
We demonstrate how to systematically test a well-motivated mechanism for
neutrino mass generation (Type-II seesaw) at the LHC, in which a Higgs triplet
is introduced. In the optimistic scenarios with a small Higgs triplet vacuum
expectation value vd < 10^{-4} GeV, one can look for clean signals of lepton
number violation in the decays of doubly charged and singly charged Higgs
bosons to distinguish the Normal Hierarchy (NH), the Inverted Hierarchy (IH)
and the Quasi-Degenerate (QD) spectrum for the light neutrino masses. The
observation of either H+ --> tau+ nubar or H+ --> e+ nubar will be particularly
robust for the spectrum test since they are independent of the unknown Majorana
phases. The H++ decays moderately depend on a Majorana phase Phi2 in the NH,
but sensitively depend on Phi1 in the IH. In a less favorable scenario vd > 2
10^{-4} GeV, when the leptonic channels are suppressed, one needs to observe
the decays H+ --> W+ H_1 and H+ --> t bbar to confirm the triplet-doublet
mixing which in turn implies the existence of the same gauge-invariant
interaction between the lepton doublet and the Higgs triplet responsible for
the neutrino mass generation. In the most optimistic situation, vd approx
10^{-4} GeV, both channels of the lepton pairs and gauge boson pairs may be
available simultaneously. The determination of their relative branching
fractions would give a measurement for the value of vd.Comment: 50 pages, 51 figures, minor corrections, one reference added, to
appear in Physical Review
CP asymmetries in B0 decays in the left-right model
We study time dependent CP asymmetries in B^0_{d,s} decays in the left-right
model with spontaneous breakdown of CP. Due to the new contributions to
B^0-\bar B^0 mixing the CP asymmetries can be substantially modified. Moreover,
there can be significant new contributions to the -meson decay amplitudes
from the magnetic penguins. Most promising for detection of the new physics in
the planned factories is that the CP asymmetries in the decays B--> J/\psi
K_S and B--> \phi K_S which are supposed to be equal in the standard model can
differ significantly in this class of models independently of the results in
the measurements of B--> X_s \gamma.Comment: Revised version, to appear in PR
Left-right symmetry at LHC and precise 1-loop low energy data
Despite many tests, even the Minimal Manifest Left-Right Symmetric Model
(MLRSM) has never been ultimately confirmed or falsified. LHC gives a new
possibility to test directly the most conservative version of left-right
symmetric models at so far not reachable energy scales. If we take into account
precise limits on the model which come from low energy processes, like the muon
decay, possible LHC signals are strongly limited through the correlations of
parameters among heavy neutrinos, heavy gauge bosons and heavy Higgs particles.
To illustrate the situation in the context of LHC, we consider the "golden"
process . For instance, in a case of degenerate heavy neutrinos
and heavy Higgs masses at 15 TeV (in agreement with FCNC bounds) we get
fb at TeV which is consistent with muon
decay data for a very limited masses in the range (3008 GeV, 3040 GeV).
Without restrictions coming from the muon data, masses would be in the
range (1.0 TeV, 3.5 TeV). Influence of heavy Higgs particles themselves on the
considered LHC process is negligible (the same is true for the light, SM
neutral Higgs scalar analog). In the paper decay modes of the right-handed
heavy gauge bosons and heavy neutrinos are also discussed. Both scenarios with
typical see-saw light-heavy neutrino mixings and the mixings which are
independent of heavy neutrino masses are considered. In the second case heavy
neutrino decays to the heavy charged gauge bosons not necessarily dominate over
decay modes which include only light, SM-like particles.Comment: 16 pages, 10 figs, KL-KS and new ATLAS limits taken into accoun
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