Probing eμ flavor-violating ALP at Belle II Endo, Motoi; Iguro, Syuhei; Kitahara, Teppei
The journal of high energy physics,
06/2020, Letnik:
2020, Številka:
6
Journal Article
Recenzirano
Odprti dostop
A
bstract
Recently, it was pointed out that the electron and muon
g −
2 discrepancies can be explained simultaneously by a single flavor-violating axion-like particle (ALP). We show that the ...parameter regions favored by the muon
g −
2 are already excluded by the muonium-antimuonium oscillation bound. In contrast, those for the electron
g −
2 can be consistent with this bound when the ALP is heavier than 1
.
5 GeV. We propose to search for a signature of the same-sign and same-flavor lepton pairs and the forward-backward muon asymmetry to test the model at the Belle II experiment.
A
bstract
The Fermilab Muon
g
−
2 collaboration recently announced the first result of measurement of the muon anomalous magnetic moment (
g
−
2), which confirmed the previous result at the ...Brookhaven National Laboratory and thus the discrepancy with its Standard Model prediction. We revisit low-scale supersymmetric models that are naturally capable to solve the muon
g
−
2 anomaly, focusing on two distinct scenarios: chargino-contribution dominated and pure-bino-contribution dominated scenarios. It is shown that the slepton pair-production searches have excluded broad parameter spaces for both two scenarios, but they are not closed yet. For the chargino-dominated scenario, the models with
m
μ
˜
L
≳
m
χ
˜
1
±
are still widely allowed. For the bino-dominated scenario, we find that, although slightly non-trivial, the region with low tan
β
with heavy higgsinos is preferred. In the case of universal slepton masses, the low mass regions with
m
μ
˜
≲ 230 GeV can explain the
g
−
2 anomaly while satisfying the LHC constraints. Furthermore, we checked that the stau-bino coannihilation works properly to realize the bino thermal relic dark matter. We also investigate heavy staus case for the bino-dominated scenario, where the parameter region that can explain the muon
g
−
2 anomaly is stretched to
m
μ
˜
≲ 1
.
3 TeV.
A
bstract
We apply on-shell methods to the bottom-up construction of electroweak amplitudes, allowing for both renormalizable and non-renormalizable interactions. We use the little-group covariant ...massive-spinor formalism, and flesh out some of its details along the way. Thanks to the compact form of the resulting amplitudes, many of their properties, and in particular the constraints of perturbative unitarity, are easily seen in this formalism. Our approach is purely bottom-up, assuming just the standard-model electroweak spectrum as well as the conservation of electric charge and fermion number. The most general massive three-point amplitudes consistent with these symmetries are derived and studied in detail, as the primary building blocks for the construction of scattering amplitudes. We employ a simple argument, based on tree-level unitarity of four-point amplitudes, to identify the three-point amplitudes that are non-renormalizable at tree level. This bottom-up analysis remarkably reproduces many low-energy relations implied by electroweak symmetry through the standard-model Higgs mechanism and beyond it. We then discuss four-point amplitudes. The gluing of three-point amplitudes into four-point amplitudes in the massive spinor helicity formalism is clarified. As an example, we work out the
ψ
c
ψ Zh
amplitude, including also the non-factorizable part. The latter is an all-order expression in the effective-field-theory expansion. Further constraints on the couplings are obtained by requiring perturbative unitarity. In the
ψ
c
ψ Zh
example, one for instance obtains the renormalizable-level relations between vector and fermion masses and gauge and Yukawa couplings. We supplement our bottom-up derivations with a matching of three- and fourpoint amplitude coefficients onto the standard-model effective field theory (SMEFT) in the broken electroweak phase. This establishes the correspondence with the usual Lagrangian approach and paves the way for SMEFT computations in the on-shell formalism.
A
bstract
The ATLAS and CMS collaborations discovered a new boson particle. If the new boson is the Higgs boson, the diphoton signal strength is 1.5 - 1.8 times larger than the Standard Model (SM) ...prediction, while the
W W
and
ZZ
signal strengths are in agreement with the SM one. In the Minimal Supersymmetric Standard Model (MSSM), overall consistency can be achieved by a light stau and the large left-right mixing of staus. However, a light stau and large left-right mixing of staus may suffer from vacuum instability. We first apply the vacuum meta-stability condition to the Higgs to diphoton decay rate in the MSSM. We show that the vacuum meta-stablity severely constrains the enhancement to the Higgs to diphoton rate. For example, when the lighter stau mass is 100 GeV, the upper bound on the enhancement to the Higgs to diphoton rate becomes 25%.
Constructing massive on-shell contact terms Durieux, Gauthier; Kitahara, Teppei; Machado, Camila S. ...
The journal of high energy physics,
12/2020, Letnik:
2020, Številka:
12
Journal Article
Recenzirano
Odprti dostop
A
bstract
The purely on-shell approach to effective field theories requires the construction of independent contact terms. Employing the little-group-covariant massive-spinor formalism, we present ...the first systematic derivation of independent four-point contact terms involving massive scalars, spin-1
/
2 fermions, and vectors. Independent three-point amplitudes are also listed for massive particles up to spin-3. We make extensive use of the simple relations between massless and massive amplitudes in this formalism. Our general results are specialized to the (broken-phase) particle content of the electroweak sector of the standard model. The (anti)symmetrization among identical particles is then accounted for. This work opens the way for the on-shell computation of massive four-point amplitudes.
A
bstract
There are two tensions related to the Cabibbo angle of the CKM matrix. First, the determinations of
V
us
from
K
μ
2
,
K
ℓ
3
, and
τ
decays disagree at the 3
σ
level. Second, using the ...average of these results in combination with
β
decays (including super-allowed
β
decays and neutron decay), a deficit in first-row CKM unitarity with a significance of again about 3
σ
is found. These discrepancies, known as the Cabibbo Angle anomaly, can in principle be solved by modifications of
W
boson couplings to quarks. However, due to SU(2)
L
invariance,
Z
couplings to quarks are also modified and flavour changing neutral currents can occur. In order to consistently assess the agreement of a new physics hypothesis with data, we perform a combined analysis for all dimension-six Standard Model Effective Field Theory operators that generate modified
W
couplings to first and second generation quarks. We then study models with vector-like quarks, which are prime candidates for a corresponding UV completion as they can affect
W
-quark couplings at tree level, and we perform a global fit including flavour observables (in particular loop effects in ∆
F
= 2 processes). We find that the best fit can be obtained for the SU(2)
L
doublet vector-like quark
Q
as it can generate right-handed
W
-
u
-
d
and
W
-
u
-
s
couplings as preferred by data.
Recently, the CMS collaboration has reported a di-tau excess with a local significance of 2.6–3.1
σ
where the invariant mass is
m
τ
τ
=
95
–100 GeV. This excess can be interpreted as a light scalar ...boson that couples to the third generation fermions, particularly top and
τ
. Based on the simplest model that can account for the CMS di-tau excess, we evaluate experimental sensitivities to the additional light resonance, using the results reported by the ATLAS collaboration. We see that a search for the top-quark associated production of the SM Higgs boson that decays into
τ
τ
¯
sets a strong model-independent limit. We also find that the CP-even scalar interpretation of the light resonance is excluded by the ATLAS results, while the CP-odd interpretation is not.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
Supersymmetric models with sub-TeV charginos and sleptons have been a candidate for the origin of the long-standing discrepancy in the muon anomalous magnetic moment (
g −
2). By gathering ...all the available LHC Run 2 results, we investigate the latest LHC constraints on models that explain the anomaly by their chargino contribution to the muon
g −
2. It is shown that the parameter regions where sleptons are lighter than charginos are strongly disfavored. In contrast, we find that the models with
m
μ
˜
L
>
~
m
χ
˜
1
±
are still widely allowed, where the lighter chargino dominantly decays into a
W
-boson and a neutralino.
New physics contributions to the Z penguin are revisited in the light of the recently-reported discrepancy of the direct CP violation in K→ππ. Interference effects between the standard model and new ...physics contributions to ΔS=2 observables are taken into account. Although the effects are overlooked in the literature, they make experimental bounds significantly severer. It is shown that the new physics contributions must be tuned to enhance B(KL→π0νν¯), if the discrepancy of the direct CP violation is explained with satisfying the experimental constraints. The branching ratio can be as large as 6×10−10 when the contributions are tuned at the 10% level.
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