8,298 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 the Type II Seesaw Mechanism: Observability of Neutral Scalars in the Nondegenerate Case
This is a sequel to our previous work on LHC phenomenology of the type II
seesaw model in the nondegenerate case. In this work, we further study the pair
and associated production of the neutral scalars H^0/A^0. We restrict ourselves
to the so-called negative scenario characterized by the mass order
M_{H^{\pm\pm}}>M_{H^\pm}>M_{H^0/A^0}, in which the H^0/A^0 production receives
significant enhancement from cascade decays of the charged scalars
H^{\pm\pm},~H^\pm. We consider three important signal
channels---b\bar{b}\gamma\gamma, b\bar{b}\tau^+\tau^-,
---and perform detailed simulations. We find
that at the 14 TeV LHC with an integrated luminosity of 3000/fb, a 5\sigma mass
reach of 151, 150, and 180 GeV, respectively, is possible in the three channels
from the pure Drell-Yan H^0A^0 production, while the cascade-decay-enhanced
H^0/A^0 production can push the mass limit further to 164, 177, and 200 GeV.
The neutral scalars in the negative scenario are thus accessible at LHC run II.Comment: v1: 32 pages, 17 figures, 3 tables. v2: added 2 refs (2nd in [61] and
[66]), revised Acknowledgments, and corrected grammatical errors according to
proofs; no other change
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