A
bstract
Models of radiative Majorana neutrino masses require new scalars and/or fermions to induce lepton-number-violating interactions. We show that these new particles also generate observable ...neutrino non-standard interactions (NSI) with matter. We classify radiative models as type-I or II, with type-I models containing at least one Standard Model (SM) particle inside the loop diagram generating neutrino mass, and type- II models having no SM particle inside the loop. While type-II radiative models do not generate NSI at tree-level, popular models which fall under the type-I category are shown, somewhat surprisingly, to generate observable NSI at tree-level, while being consistent with direct and indirect constraints from colliders, electroweak precision data and charged-lepton flavor violation (cLFV). We survey such models where neutrino masses arise at one, two and three loops. In the prototypical Zee model which generates neutrino masses via one-loop diagrams involving charged scalars, we find that diagonal NSI can be as large as (8%
,
3
.
8%
,
9
.
3%) for (
ε
ee
, ε
μμ
, ε
ττ
), while off-diagonal NSI can be at most (10
−
3
%
,
0
.
56%
,
0
.
34%) for (
ε
eμ
, ε
eτ
, ε
μτ
). In one-loop neutrino mass models using leptoquarks (LQs), (
ε
μμ
, ε
ττ
) can be as large as (21
.
6%
,
51
.
7%), while
ε
ee
and (
ε
eμ
, ε
eτ
, ε
μτ
) can at most be 0.6%. Other two- and three-loop LQ models are found to give NSI of similar strength. The most stringent constraints on the diagonal NSI are found to come from neutrino oscillation and scattering experiments, while the off-diagonal NSI are mostly constrained by low-energy processes, such as atomic parity violation and cLFV. We also comment on the future sensitivity of these radiative models in long-baseline neutrino experiments, such as DUNE. While our analysis is focused on radiative neutrino mass models, it essentially covers all NSI possibilities with heavy mediators.
A
bstract
The excess in electron recoil events reported recently by the XENON1T experiment may be interpreted as evidence for a sizable transition magnetic moment
μ
v
e
v
μ
of Majorana neutrinos. We ...show the consistency of this scenario when a single component transition magnetic moment takes values
μ
v
e
v
μ
∈
1.65
−
3.42
×
10
−
11
μ
B
. Such a large value typically leads to unacceptably large neutrino masses. In this paper we show that new leptonic symmetries can solve this problem and demonstrate this with several examples. We first revive and then propose a simplified model based on SU(2)
H
horizontal symmetry. Owing to the difference in their Lorentz structures, in the SU(2)
H
symmetric limit,
m
ν
vanishes while
μ
v
e
v
μ
is nonzero. Our simplified model is based on an approximate SU(2)
H
, which we also generalize to a three family SU(3)
H
-symmetry. Collider and low energy tests of these models are analyzed. We have also analyzed implications of the XENON1T data for the Zee model and its extensions which naturally generate a large
μ
v
e
v
μ
with suppressed
m
ν
via a spin symmetry mechanism, but found that the induced
μ
v
e
v
μ
is not large enough to explain recent data. Finally, we suggest a mechanism to evade stringent astrophysical limits on neutrino magnetic moments arising from stellar evolution by inducing a medium-dependent mass for the neutrino.
A
bstract
We present a model of radiative neutrino masses which also resolves anomalies reported in
B
-meson decays,
R
D
∗
and
R
K
∗
, as well as in muon
g −
2 measurement, ∆
a
μ
. Neutrino masses ...arise in the model through loop diagrams involving TeV-scale leptoquark (LQ) scalars
R
2
and
S
3
. Fits to neutrino oscillation parameters are obtained satisfying all flavor constraints which also explain the anomalies in
R
D
∗
,
R
K
∗
and ∆
a
μ
within 1
σ
. An isospin-3/2 Higgs quadruplet plays a crucial role in generating neutrino masses; we point out that the doubly-charged scalar contained therein can be produced in the decays of the
S
3
LQ, which enhances its reach to 1.1 (6.2) TeV at
s
= 14 TeV high-luminosity LHC (
s
= 100 TeV FCC-hh). We also present flavor-dependent upper limits on the Yukawa couplings of the LQs to the first two family fermions, arising from non-resonant dilepton (
pp → ℓ
+
ℓ
−
) processes mediated by
t
-channel LQ exchange, which for 1 TeV LQ mass, are found to be in the range (0
.
15
−
0
.
36). These limits preclude any explanation of
R
D
∗
through LQ-mediated
B
-meson decays involving
ν
e
or
ν
μ
in the final state. We also find that the same Yukawa couplings responsible for the chirally-enhanced contribution to ∆
a
μ
give rise to new contributions to the SM Higgs decays to muon and tau pairs, with the modifications to the corresponding branching ratios being at (2–6)% level, which could be tested at future hadron colliders, such as HL-LHC and FCC-hh.
I present a comprehensive analysis of neutrino non-standard interactions (NSI) generated by new scalars in radiative neutrino mass models. To this end, I propose a new nomenclature for classifying ...radiative neutrino mass models: those containing at least one SM particle in the loop are designated as type-I radiative models, while those without SM particles in the loop are designated as type-II radiative models. In terms of NSI, type-I radiative models are the most intriguing, since the neutrino couples directly to an SM fermion (matter field) and a new scalar, creating NSI at the tree level, in contrast to type-II radiative models. I summarized the maximum possible NSI in all type-I radiative models after accounting for numerous theoretical and experimental restrictions. Additionally, I demonstrate that using light charged scalars in radiative models can result in a Glashow-like resonance feature in the UHE neutrino event spectrum at the IceCube neutrino observatory and its high-energy upgrade IceCube-Gen2, which can probe a sizable fraction of the allowed NSI parameter space. This talk is based on results obtained with K.S. Babu, Bhupal Dev, Anil Thapa and Yicong Sui and presented in hep-ph 1907.09498 and 1908.02779.
A
bstract
We show that the rate for di-Higgs production at the LHC can be enhanced by a factor as large as 25 compared to the Standard Model value in the two Higgs doublet model, while being ...consistent with the known properties of the observed Higgs boson
h
. There are correlated modifications in
t
t
¯
h
and resonant
Zh
production rates, which can serve as tests of this model. Our framework treats both Higgs doublets on equal footing, each with comparable Yukawa couplings to fermions. The Cheng-Sher ansatz for multi-Higgs doublet model is shown to be strongly disfavored by current experiments. We propose a new ansatz for the Yukawa couplings of the Higgs doublets Φ
a
is proposed, where
Y
ij
(
a
)
=
C
ij
(
a
)
· min{
m
i
,
m
j
}/
v
, with
C
ij
(
a
)
being order one coefficients,
m
i the mass of fermion
i
and
v
the electroweak vacuum expectation value. Such a pattern of couplings can explain the observed features of fermion masses and mixings and satisfies all flavor violation constraints arising from the exchange of neutral Higgs bosons. The rate for
μ
→
eγ
decay and new contributions to CP violation in
B
s
−
B
¯
s
mixing are predicted to be close to the experimental limits.
Neutrinos may be the harbingers of new dark sectors, since the renormalizable neutrino portal allows for their interactions with hidden new physics. We propose here to use this fact to connect the ...generation of neutrino masses to a light dark sector, charged under a new U(1)D dark gauge symmetry. We introduce the minimal number of dark fields to obtain an anomaly free theory with spontaneous breaking of the dark symmetry, and obtain automatically the inverse seesaw Lagrangian. In addition, the so-called μ-term of the inverse seesaw is dynamically generated and technically natural in this framework. As a bonus, the new light dark gauge boson can provide a possible explanation to the MiniBooNE anomaly.
The muon anomalous magnetic moment measurement has, for more than a decade, been a long-standing anomaly hinting the physics beyond the Standard Model (BSM). The recently announced results from muon ...g−2 collaboration, corresponding to 3.3σ deviation from Standard Model value (4.2σ in combination with previous measurement) are strengthening the need for new physics coupled to muons. In this letter, we propose a novel scenario in which Standard Model (SM) is augmented by an axion-like particle (ALP) and vector-like fermions. We find that such a model admits an excellent interpretation of recent muon g−2 measurement through quantum process featuring ALP interacting with muons and newly introduced fermions. Previously proposed explanations with ALPs utilize interactions with photons and/or SM fermions. Therefore, in this letter we complement and extend such scenarios. We also discuss collider prospects for the model as well as the possibility that ALP is long lived or stable dark matter (DM) candidate.
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