We investigate nuclear
μ
−
–
e
−
conversion in the framework of an effective Lagrangian arising from the inverse seesaw model of neutrino masses. We consider lepton flavour violation interactions ...that arise from short range (non-photonic) as well as long range (photonic) contributions. Upper bounds for the
L̸
f
-parameters characterizing
μ
−
–
e
−
conversion are derived in the inverse seesaw model Lagrangian using the available limits on the
μ
−
–
e
−
conversion branching ratio, as well as the expected sensitivities of upcoming experiments. We comment on the relative importance of these two types of contributions and their relationship with the measured solar neutrino mixing angle
θ
12
and the dependence on
θ
13
. Finally we show how the
L̸
f
μ
−
–
e
−
conversion and the
μ
−
→
e
−
γ
rates are strongly correlated in this model.
Searching for heavy neutral gauge bosons Z′, predicted in extensions of the Standard Model based on a U(1)′ gauge symmetry, is one of the challenging objectives of the experiments carried out at the ...Large Hadron Collider. In this paper, we study Z′ phenomenology at hadron colliders according to several U(1)′-based models and in the Sequential Standard Model. In particular, possible Z′ decays into supersymmetric particles are included, in addition to the Standard Model modes so far investigated. We point out the impact of the U(1)′ group on the MSSM spectrum and, for a better understanding, we consider a few benchmarks points in the parameter space. We account for the D-term contribution, due to the breaking of U(1)′, to slepton and squark masses and investigate its effect on Z′ decays into sfermions. Results on branching ratios and cross sections are presented, as a function of the MSSM and U(1)′ parameters, which are varied within suitable ranges. We pay special attention to final states with leptons and missing energy and make predictions on the number of events with sparticle production in Z′ decays, for a few values of integrated luminosity and centre-of-mass energy of the LHC.
The fundamental nature of the neutrino is presently a subject of great interest. A way to access the absolute mass scale and the fundamental nature of the neutrino is to utilize the atomic nuclei ...through their rare decays, the neutrinoless double beta (0ν
ββ
) decay in particular. The experimentally measurable observable is the half-life of the decay, which can be factorized to consist of phase space factor, axial vector coupling constant, nuclear matrix element, and function containing physics beyond the standard model. Thus reliable description of nuclear matrix element is of crucial importance in order to extract information governed by the function containing physics beyond the standard model, neutrino mass parameter in particular. Comparison of double beta decay nuclear matrix elements obtained using microscopic interacting boson model (IBM-2) and quasiparticle random phase approximation (QRPA) has revealed close correspondence, even though the assumptions in these two models are rather different. The origin of this compatibility is not yet clear, and thorough investigation of decomposed matrix elements in terms of different contributions arising from induced currents and the finite nucleon size is expected to contribute to more accurate values for the double beta decay nuclear matrix elements. Such comparison is performed using detailed calculations on both models and obtained results are then discussed together with recent experimental results.
We consider the implications of the recent measurement of the W-boson mass MW=80,433.5±9.4MeV/c2 for atomic parity violation experiments. We show that the change in MW shifts the Standard Model ...prediction for the 133Cs nuclear weak charge to QW(133Cs)=−73.11(1), i.e., by 8.5σ from its current value, and the proton weak charge by 2.7%. The shift in QW(133Cs) ameliorates the tension between existing determinations of its value and motivates more accurate atomic theory calculations, while the shift in QW(p) inspires next-generation atomic parity violation experiments with hydrogen. Using our revised value for QW(133Cs), we also readjust constraints on parameters of physics beyond the Standard Model. Finally, we reexamine the running of the electroweak coupling for the new W boson mass.
A search for new massive resonances decaying to a dielectron or a dimuon pair is presented. The search uses the full dataset corresponding to an integrated luminosity of about 20 fb−1 of pp ...collisions at a center-of-mass energy of 8 TeV, collected by the CMS experiment in 2012. In absence of a significant deviation from the standard model predictions, 95% confidence level limits are set on the ratio of cross section times branching ratio of a new resonance to the cross section times branching ratio of the Z boson. A sequential standard model ZSSM′ and a superstring-inspired Zψ′ of mass lighter than 2960 GeV and 2600 GeV, respectively, can be excluded at 95% confidence level.
IceCube has recently observed 37 events of TeV–PeV energies. The angular distribution, with a strong preference for downgoing directions, the spectrum, and the small muon to shower ratio in the data ...cannot be accommodated assuming standard interactions of atmospheric neutrinos. We obtain an excellent fit, however, if a diffuse flux of ultrahigh energy (cosmogenic) neutrinos experiences collisions where only a small fraction of the energy is transferred to the target nucleon. We show that consistent models of TeV gravity or other non-Wilsonian completions of the standard model provide cross sections with these precise features. An increased statistics could clearly distinguish our scenario from the one assumed by IceCube (a diffuse flux of astrophysical neutrinos with a ∝E-2 spectrum) and establish the need for new physics in the interpretation of the data.
If the Standard Model (SM) of elementary particle physics is assumed to hold good to arbitrarily high energies, then, for the best fit values of the parameters, the scalar potential of the Standard ...Model Higgs field turns negative at a high scale μinst. If the physics beyond the SM is such that it does not modify this feature of the Higgs potential and if the Hubble parameter during inflation (Hinf) is such that Hinf≫μinst, then, quantum fluctuations of the SM Higgs during inflation make it extremely unlikely that after inflation it will be found in the metastable vacuum at the weak scale. In this work, we assume that (i) during inflation, the SM Higgs is in Bunch–Davies vacuum state, and, (ii) the question about the stability of the effective potential must be answered in the frame of the freely falling observer (just like in Minkowski spacetime), and then use the well-known fact that the freely falling observer finds Bunch–Davies vacuum to be in thermal state to show that the probability to end up in the electroweak vacuum after inflation is reasonably high.
No evidence of “new physics” was found so far by LHC experiments, and this situation has led some voices in the physics community to call for the abandonment of the “naturalness” criterion, while ...other scientists have felt the need to break a lance in its defense by claiming that, at least in some sense, it has already led to successes and therefore should not be dismissed too quickly, but rather only reflected or reshaped to fit new needs. In our paper we will argue that present pro-or-contra naturalness debates miss the fundamental point that naturalness, despite contrary claims, is essentially a very hazily defined, in a sense even mythical notion which, in the course of more than four decades, has been steadily, and often not coherently, shaped by its interplay with different branches of model-building in high-energy physics and cosmology on the one side, and new incoming experimental results on the other. In our paper we will endeavor to clear up some of the physical and philosophical haze by taking a closer look back at (real or alleged) origin of naturalness in the 1970s and 1980s, with particular attention to the early work of Kenneth Wilson. In doing this, we aim to bring to light how naturalness belongs to a long tradition of present and past physical and philosophical criteria for effectively guiding theoretical reflection and experimental practice in fundamental research.
This is an introductory review of the main features of leptogenesis, one of the most attractive models of baryogenesis for the explanation of the matter-antimatter asymmetry of the Universe. The ...calculation of the asymmetry in leptogenesis is intimately related to neutrino properties so that leptogenesis is also an important phenomenological tool to test the see-saw mechanism for the generation of neutrino masses and mixing and the underlying theory beyond the Standard Model.
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