20,873 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
Determining the nature of white dwarfs from low-frequency gravitational waves
An extreme-mass-ratio system composed of a white dwarf (WD) and a massive
black hole can be observed by the low-frequency gravitational wave detectors,
such as the Laser Interferometer Space Antenna (LISA). When the mass of the
black hole is around , the WD will be disrupted by the
tidal interaction at the final inspiraling stage. The event position and time
of the tidal disruption of the WD can be accurately determined by the
gravitational wave signals. Such position and time depend upon the mass of the
black hole and especially on the density of the WD. We present the theory by
using LISA-like gravitational wave detectors, the mass-radius relation and then
the equations of state of WDs could be strictly constrained (accuracy up to
). We also point out that LISA can accurately predict the disruption
time of a WD, and forecast the electromagnetic follow-up of this tidal
disruption event.Comment: 7 pages, 2 figure
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
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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