Does H → γγ taste like vanilla new physics? Almeida, L. G.; Bertuzzo, E.; Machado, P. A. N. ...
The journal of high energy physics,
11/2012, Letnik:
2012, Številka:
11
Journal Article
Recenzirano
Odprti dostop
A
bstract
We analyse the interplay between the Higgs to diphoton rate and electroweak precision measurements constraints in extensions of the Standard Model with new uncolored charged fermions that ...do not mix with the ordinary ones. We also compute the pair production cross sections for the lightest fermion and compare them with current bounds.
We discuss weak kaon decays in a scenario in which the Standard Model is extended by massive sterile fermions. After revisiting the analytical expressions for leptonic and semileptonic decays we ...derive the expressions for decay rates with two neutrinos in the final state. By using a simple effective model with only one sterile neutrino, compatible with all current experimental bounds and general theoretical constraints, we conduct a thorough numerical analysis which reveals that the impact of the presence of massive sterile neutrinos on kaon weak decays is very small, less than 1% on decay rates. The only exception is B(KL→νν), which can go up to O(10−10), thus possibly within the reach of the KOTO, NA62 and SHIP experiments. Plans have also been proposed to search for this decay at the NA64 experiment. In other words, if all the future measurements of weak kaon decays turn out to be compatible with the Standard Model predictions, this will not rule out the existence of massive light sterile neutrinos with non-negligible active-sterile mixing. Instead, for a sterile neutrino of mass below mK, one might obtain a huge enhancement of B(KL→νν), otherwise negligibly small in the Standard Model.
A
bstract
We discuss how the lepton CP phase can be constrained by accelerator and reactor measurements in an era without dedicated experiments for CP violation search. To characterize globally the ...sensitivity to the CP phase
δ
CP
, we use the CP exclusion fraction, which quantifies what fraction of the
δ
CP
space can be excluded at given input values of
θ
23
and
δ
CP
. Using the measure we study the CP sensitivity which may be possessed by the accelerator experiments T2K and NO
ν
A. We show that, if the mass hierarchy is known, T2K and NO
ν
A alone may exclude, respectively, about 50%-60% and 40%-50% of the
δ
CP
space at 90% CL by 10 years running, provided that a considerable fraction of beam time is devoted to the antineutrino run. The synergy between T2K and NO
ν
A is remarkable, leading to the determination of the mass hierarchy through CP sensitivity at the same CL.
A
bstract
The lepton mixing angle
θ
13
, the only unknown angle in the standard three-flavor neutrino mixing scheme, is finally measured by the recent reactor and accelerator neutrino experiments. We ...perform a combined analysis of the data coming from T2K, MINOS, Double Chooz, Daya Bay and RENO experiments and find sin
2
2
θ
13
= 0.096 ± 0.013(±0.040) at 1
σ
(3
σ
) CL and that the hypothesis
θ
13
= 0 is now rejected at a significance level of 7.7
σ
. We also discuss the near future expectation on the precision of the
θ
13
determination by using expected data from these ongoing experiments.
A
bstract
We study the constraints that electroweak precision data can impose, after the discovery of the Higgs boson by the LHC, on neutrinophilic two-Higgs-doublet models which comprise one extra ...SU(2) × U(1) doublet and a new symmetry, namely a spontaneously broken
ℤ
2
or a softly broken global U(1). In these models the extra Higgs doublet, via its very small vacuum expectation value, is the sole responsible for neutrino masses. We find that the model with a
ℤ
2
symmetry is basically ruled out by electroweak precision data, even if the model is slightly extended to include extra right-handed neutrinos, due to the presence of a very light scalar. While the other model is still perfectly viable, the parameter space is considerably constrained by current data, specially by the
T
parameter. In particular, the new charged and neutral scalars must have very similar masses.
In neutrino oscillation with non-standard interactions (NSI) the system is enriched with CP violation caused by phases due to NSI in addition to the standard lepton Kobayashi-Maskawa phase δ. In this ...paper we show that it is possible to disentangle the two CP violating effects by measurement of muon neutrino appearance by a near-far two detector setting in neutrino factory experiments. Prior to the quantitative analysis we investigate in detail the various features of the neutrino oscillations with NSI, but under the assumption that only one of the NSI elements, ε
e
μ
or ε
e
τ
, is present. They include synergy between the near and the far detectors, the characteristic differences between the ε
e
μ
and ε
e
τ
systems, and in particular, the parameter degeneracy. Finally, we use a concrete setting with the muon energy of 50GeV and magnetized iron detectors at two baselines, one at
L
= 3000 km and the other at
L
= 7000 km, each having a fiducial mass of 50 kton to study the discovery potential of NSI and its CP violation effects. We demonstrate, by assuming 4 × 10
21
useful muon decays for both polarities, that one can identify nonstandard CP violation down to |ε
e
μ
| ≃ a few × 10
−3
, and |ε
e
τ
| ≃ 10
−2
at 3σ CL for θ
13
down to sin
2
2θ
13
= 10
−4
in most of the region of δ. The impact of the existence of NSI on the measurement of δ and the mass hierarchy is also worked out.
Can new colored particles illuminate the Higgs? Bertuzzo, E.; Machado, P. A. N.; Funchal, R. Zukanovich
The journal of high energy physics,
02/2013, Letnik:
2013, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A
bstract
We analyze the behavior of Higgs to diphoton rate and Higgs gluon-gluon production cross section in minimal extensions of the Standard Model comprising new colored vector-like fermions that ...do not mix with the ordinary ones. We compare these information with constraints coming from electroweak precision measurements. We compute pair production cross sections for the lightest fermion and discuss the LHC bounds. Finally, we study the phenomenology of possible quarkonium states composed by thesenew colored fermions.
A
bstract
We examine various scenarios that involve a light
O
(1 TeV) leptoquark state and select those which are compatible with the current experimental values for ℬ(
B
s
→
μμ
),
ℬ
B
→
K
μ
μ
...large
−
q
2
,
R
K
=
ℬ
′
B
→
K
μ
μ
/
ℬ
′
B
→
K
e
e
, and which lead to predictions consistent with other experimental data. We show that two such scenarios are phenomenologically plausible, namely the one with a doublet of scalar leptoquarks of hypercharge 1
/
6, and the one with a triplet of vector leptoquarks of hypercharge 2
/
3. We also argue that a model with a singlet scalar leptoquark of hypercharge 1
/
3 is not viable. Using the present experimental data as constraints, it is shown that the exclusive lepton flavor violating decays, ℬ(
B
s
→
μτ
), ℬ(
B
→
Kμτ
) and ℬ(
B
→
K
∗
μτ
), can be as large as
O
1
0
−
5
.
We show in this Letter that the observation of the angular distribution of upward-going muons and cascade events induced by atmospheric neutrinos at the TeV energy scale, which can be performed by a ...kilometer-scale neutrino telescope, such as the IceCube detector, can be used to probe a large neutrino mass splitting, |Δm2|∼(0.5–2.0) eV2, implied by the LSND experiment and discriminate among four neutrino mass schemes. This is due to the fact that such a large mass scale can promote non-negligible νμ→νe,ντ/ν̄μ→ν̄e,ν̄τ conversions at these energies by the MSW effect as well as vacuum oscillation, unlike what is expected if all the neutrino mass splittings are small.
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