8,297 research outputs found
Naturally Small Dirac Neutrino Mass with Intermediate Multiplet Fields
If neutrinos are Dirac fermions, certain new physics beyond the standard
model should exist to account for the smallness of neutrino mass. With two
additional scalars and a heavy intermediate fermion, in this paper, we
systematically study the general mechanism that can natrally generate the tiny
Dirac neutrino mass at tree and in one-loop level. For tree level models, we
focus on natural ones, in which the additional scalars develop small vacuum
expectation values without fine-tuning. For one-loop level models, we explore
those having dark matter candidates under symmetry. In both cases, we
concentrate on multiplet scalars no larger than quintuplet, and
derive the complete sets of viable models. Phenomenologies, such as lepton
flavor violation, leptogenesis, and LHC signatures are briefly discussed.Comment: 31 pages, 16 figure
Ozone Measurements with Meteors: A Revisit
Understanding the role of ozone in the Mesosphere/Lower Thermosphere (MLT)
region is essential for understanding the atmospheric processes in the upper
atmosphere. Earlier studies have shown that it is possible to use overdense
meteor trails to measure ozone concentration in the meteor region. Here we
revisit this topic by comparing a compilation of radar observations to
satellite measurements. We observe a modest agreement between the values
derived from these two methods, which confirm the usefulness of the meteor
trail technique for measuring ozone content at certain heights in the MLT
region. Future simultaneous measurements will help quantifying the performance
of this technique.Comment: MNRAS in pres
The Scotogenic Models for Dirac Neutrino Masses
We construct the one-loop and two-loop scotogenic models for Dirac neutrino
mass generation in the context of extensions of standard model. It
is indicated that the total number of intermediate fermion singlets is uniquely
fixed by anomaly free condition and the new particles may have exotic
charges so that the direct SM Yukawa mass term
and the Majorana mass term
are naturally forbidden. After the spontaneous
breaking of symmetry, the discrete or symmetry
appears as the residual symmetry and give rise to the stability of
intermediated fields as DM candidate. Phenomenological aspects of lepton flavor
violation, DM, leptogenesis and LHC signatures are discussed.Comment: 18 pages, 16 figure
LHC Phenomenology of Type II Seesaw: Nondegenerate Case
In this paper, we thoroughly investigate the LHC phenomenology of the type II
seesaw mechanism for neutrino masses in the nondegenerate case where the
triplet scalars of various charge () have
different masses. Compared with the degenerate case, the cascade decays of
scalars lead to many new, interesting signal channels. In the positive scenario
where , the four-lepton signal is still
the most promising discovery channel for the doubly-charged scalars
. The five-lepton signal is crucial to probe the mass spectrum of
the scalars, for which, for example, a reach at 14 TeV LHC for
with requires an integrated
luminosity of 76/fb. And the six-lepton signal can be used to probe the neutral
scalars , which are usually hard to detect in the degenerate case. In
the negative scenario where , the
detection of is more challenging, when the cascade decay
is dominant. The most important channel is the
associated production in the final state
, which requires a luminosity of 109/fb
for a discovery, while the final state
is less promising. Moreover, the
associated production can give same signals as the standard model
Higgs pair production. With a much larger cross section, the
production in the final state could reach
significance at 14 TeV LHC with a luminosity of 300/fb. In summary, with an
integrated luminosity of order 500/fb, the triplet scalars can be fully
reconstructed at 14 TeV LHC in the negative scenario.Comment: 41 pages, 20 figures, 7 tables. Version 2 accepted by PRD. 41 pages,
18 figures. Main changes are, (1) rewording in secs III and IV, removing 2
figs and quoting ref [34]; (2) a paragraph added before eq (10) to clarify
constraints from electroweak precision data; (3) a paper added to ref [11].
No changes in result
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