Model Of Electroweak Interactions Research Articles

Two-measure approach to breaking scale-invariance in a standard-model extension

Abstract We introduce Weyl's scale-invariance as an additional global symmetry in the standard model of electroweak interactions. A natural consequence is the introduction of general relativity coupled to scalar fields a la Dirac, that includes the Higgs doublet and a singlet σ-field required for implementing global scale-invariance. We introduce a mechanism for ‘spontaneous breaking’ of scale-invariance by introducing a coupling of the σ-field to a new metric-independent measure Φ defined in terms of four scalars ϕ i ( i = 1 , 2 , 3 , 4 ) . Global scale-invariance is regained by combining it with internal diffeomorphism of these four scalars. We show that once the global scale-invariance is broken, the phenomenon (a) generates Newton's gravitational constant G N and (b) triggers spontaneous symmetry breaking in the normal manner resulting in masses for the conventional fermions and bosons. In the absence of fine-tuning the scale at which the scale-symmetry breaks can be of order Planck mass. If right-handed neutrinos are also introduced, their absence at present energy scales is attributed to their mass terms tied to the scale where scale-invariance breaks.

Why supersymmetry? Physics beyond the standard model

The Naturalness Principle as a requirement that the heavy mass scales decouple from the physics of light mass scales is reviewed. In quantum field theories containing elementary scalar fields, such as the Standard Model of electroweak interactions containing the Higgs particle, mass of the scalar field is not a natural parameter as it receives large radiative corrections. How supersymmetry solves this Naturalness Problem is outlined. There are also other contexts where the presence of elementary scalar fields generically spoils the high–low mass scales decoupling in the quantum theory. As an example of this, the non-decoupling of possible Planck scale violation of Lorentz invariance due to quantum gravity effects from the physics at low scales in theories with elementary scalar fields such as the Higgs field is described. Here again supersymmetry provides a mechanism for ensuring that the decoupling of heavy–light mass scales is maintained.

RED-100 detector for the first observation of the elastic coherent neutrino scattering off xenon nuclei

The RED-100 (Russian Emission Detector) is being constructed for the experiment to search for elastic coherent neutrino scattering off atomic nuclei. This fundamental process was predicted several decades ago by the Standard Model of electroweak interactions but has not been discovered yet. The RED-100 is a two-phase emission xenon detector containing ∼200 kg of the liquid Xe (∼ 100 kg of that is in a fiducial volume). One of the possible sites to carry out the experiment is the SNS (Spallation Neutron Source) facility at Oak Ridge National Laboratory, USA. SNS is the world's most intense pulsed source of neutrinos and unique place to study neutrino properties. The energy spectrum of neutrinos produced at the SNS extends up to ∼ 50 MeV and satisfies coherence condition. These neutrinos give kinetic energies of Xe recoils up to a few tens of keV where the response of nuclear recoils is well-known from neutron calibrations of dark matter detectors. The detector will be deployed in the basement under the experimental hall at a distance of ∼30 meters from the SNS target. The expected signal and background (neutron and gamma) are estimated for this specific location. The detector details, current status and future plans are provided.

Stability of the electroweak ground state in the Standard Model and its extensions

We review the formalism by which the tunnelling probability of an unstable ground state can be computed in quantum field theory, with special reference to the Standard Model of electroweak interactions. We describe in some detail the approximations implicitly adopted in such calculation. Particular attention is devoted to the role of scale invariance, and to the different implications of scale-invariance violations due to quantum effects and possible new degrees of freedom. We show that new interactions characterized by a new energy scale, close to the Planck mass, do not invalidate the main conclusions about the stability of the Standard Model ground state derived in absence of such terms.

On some features of possible torsion effects on observables at Hadron colliders

I give a geometrical description of conformal gauge gravitational theory (CGTG) from the viewpoint of symmetries and affine structure. In the frames of the CGTG incorporating gravitation with torsion space-time into Standard Model of electro-weak interaction (EWI) the multi-muon events produced at the Fermilab Tevatron collider were studied. The CGTG gives the value of the torsion pseudotrace–spinor (muon) universal coupling fT = 4.388 ⋅ 10-17 GF, and with limits from known experiments — torsion mass mT = 0.4700 ⋅ 10-7 eV or mT = 0.445 ⋅ 10-15 muon mass. So the value of the constant of effective four-fermions interaction fT/mT = 0.988, indeed may lead to multi-muon events production. The model of interaction of quantum oscillator with the tensor potential Wμν of traceless part of the torsion lead to 2 cm displacement of quark–lepton system as a whole in the magnetic field of collider in accordance with a significant sample of events related to [Formula: see text] production and decay in which at least one of the muon candidates is produced outside of the beam pipe of radius 1.5 cm. A traceless part of the torsion in CGTG does not vanish in the Newtonian limit of nonzero mass. Torsion gravity potential Wμν gives conservation of a special conformal current and may be produced in the condition of a spontaneous breaking of gauge symmetry where the gravitation mass MX defect is 1–3 Tev ⋅ c-2 or 10-13MX. This effect may be possible at known effects on top pair asymmetries at the Tevatron and LHC and takes place as the known energy dissipation above 3 TeV of the Galaxy gamma-ray and neutrino spectrum from two bubbles outside the Galaxy plane.

Simultaneous analysis of neutrinoless double beta decay and LHC pp-cross sections: limits on the left-right mixing angle

The extension of the Standard Model of electroweak interactions, to accommodate massive neutrinos and/or right-handed currents, is one of the fundamental questions to answer in the cross-field of particle and nuclear physics. The consequences of such extensions would reflect upon nuclear decays, like the very exotic nuclear double-beta-decay, as well as upon high-energy proton-proton reactions of the type performed at the LHC accelerator. In this talk we shall address this question by looking at the results reported by the ATLAS and CMS collaborations, where the excitation and decay of a heavy-mass boson may be mediated by a heavy-mass neutrino in proton-proton reactions leading to two jets and two leptons, and by extracting limits on the left-right mixing, from the latest measurements of nuclear-double-beta decays reported by the GERDA and EXO collaborations.

Testing Left-Right extensions of the standard model of electroweak interactions with double-beta decay and LHC measurements

The minimal extension of the standard model of electroweak interactions allows for massive neutrinos, a massive right-handed boson WR, and a left-right mixing angle ζ. While an estimate of the light (electron) neutrino can be extracted from the non-observation of the neutrinoless double beta decay, the limits on the mixing angle and the mass of the righthanded (RH) boson may be extracted from a combined analysis of the double beta decay measurements (GERDA, EXO-200 and KamLAND-Zen collaborations) and ATLAS data on the two-jets two-leptons signals following the excitation of a virtual RH boson mediated by a heavy-mass neutrino. In this work we shall compare results of both types of experiments, and show that the estimates are not in tension.

Searches for direct stop production within the ATLAS experiment

The ATLAS experiment at the LHC, in conjunction with the discovery of the Higgs boson is looking for signs of physics which go beyond the Standard Model of Electroweak interactions. Among possible theories for physics beyond Standard Model, Supersymmetry seems to be the most promising one. This theory indeed addresses the Standard Model naturalness problem and offers a perfect candidate for the dark matter. Within this scenario the search for a supersymmetric partner of the top quark, called stop, plays a key role. The ATLAS Experiment has developed a dedicated strategy for the discovery of this particle, focusing on achieving a complete coverage of the available parameter space for this particle, based on the combined search for all of its possible decay modes. The results obtained using the complete ATLAS 2012 statistics will be presented, targeting different decay modes and explaining the procedure to obtain the exclusion limits on the existence of a supersymmetric partner of the top quark at the electroweak scale.

A Matter of Kuhnian Theory-Choice? The GWS Model and the Neutral Current

In the Kuhnian view of theory choice, theories, as a matter of empirical fact, often score differently with regard to the standard theoretical virtues. The case I discuss in this paper, however, is a case in which there was one theory which was more virtuous than all its competitors. In such cases practitioners' disparate weighting preferences, which Kuhn is so keen to emphasize, make no difference to theory choice: practitioners' choices will converge on one theory despite their different weighting preferences. The case I discuss in this paper concerns the Glashow-Weinberg-Salam (GWS) model of electroweak interactions in the early 1970s. After considering the contemporary experimental evidence in its favor in detail, I argue that the GWS model was chosen not because the evidence in its favor was compelling, but rather because its virtues exceeded those of its competitors.

A six-dimensional Jordan model for electroweak interactions

A six-dimensional Jordan model for electroweak interactions

Composite leptons at the LHC

In some models of electroweak interactions the W and Z bosons are considered composites, made up of spin-[Formula: see text] subconstituents. In these models a spin-0 counterpart of the W and Z boson naturally appears, whose higher mass can be attributed to a particular type of hyperfine spin interaction among the various subconstituents. Recently, it has been argued that the scalar state could be identified with the newly discovered Higgs (H) candidate. Here, we use the known spin splitting between the W/Z and H states to infer, within the framework of a purely phenomenological model, the relative strength of the spin–spin interactions. The results are then applied to the lepton sector, and used to crudely estimate the relevant spin splitting between the two lowest states. Our calculations in many ways parallels what is done in the SU(6) quark model, where most of the spin splittings between the lowest lying baryon and meson states are reasonably well-accounted for a simple color hyperfine interaction, with constituent (color-dressed) quark masses.

Composite Higgs Boson in the Unified Subquark Model of All Fundamental Particles and Forces

In the unified subquark model of all fundamental particles and forces, the mass of the Higgs boson in the standard model of electroweak interactions ($m_H$) is predicted to be about $2\sqrt{6}m_W/3$ (where $m_W$ is the mass of the charged weak boson), which agrees well with the experimental values of $125-126$ GeV recently found by the ATLAS and CMS Colaborations at the LHC. It seems to indicate that the Higgs boson is a composite of the iso-doublet subquark-antisubquark pairs well described by the unified subquark model with either one of subquark masses vanishing or being very small compared to the other.

On mass-shell renormalizability of the massive Yang-Mills theory

It is shown that the massive Yang-Mills theory is on mass-shell renormalizable. Thus the Standard Model of electroweak interactions can be modified by removing terms with the scalar field from the Lagrangian in the unitary gauge. The resulting electroweak theory without the Higgs particle is on mass-shell renormalizable and unitary.

Can we explain why leptonic electroweak interactions are chiral?

One of the fundamental ingredients in the standard model of electroweak interactions between fundamental particles is chirality. Currently there are no hints about why nature has chosen the chiral way. The answer to such a fundamental question could be the extension of the whole theory to the superluminal sector of the Lorentz-Poincaré group. Restricting ourselves to leptons, we postulate that the neutrinos are a priori described by a tachyonic Dirac Lagrangian. It could provide a simple explanation for the parity violation in weak interactions and why electroweak theory has a chiral aspect, leading to invariance under a SUL(2) × UY(1) gauge group. Right-handed neutrino becomes sterile and decoupled from the other particles quite naturally.

Lepton asymmetry growth in the symmetric phase of an electroweak plasma with hypermagnetic fields versus its washing out by sphalerons

We study lepton asymmetry evolution in plasma of the early Universe before the electroweak phase transition (EWPT) accounting for chirality flip processes via Higgs decays (inverse decays) entering equilibrium at temperatures below T_RL ~ 10 TeV, T_EW < T < T_RL. We solve appropriate kinetic equations for leptons and Higgs bosons taking into account the lepton number violation due to Abelian anomalies for right and left electrons and neutrinos in the self-consistent hypercharge field obeying Maxwell equations modified by the contribution of the Standard Model of electroweak interactions. The violation of left lepton numbers and the corresponding violation of the baryon number due to sphaleron processes in symmetric phase is taken into account as well. Assuming the Chern-Simons wave configuration of the seed hypercharge field, we get the estimates of baryon and lepton asymmetries evolved from the primordial right electron asymmetry existing alone as partial asymmetry at T > T_RL. One finds a strong dependence of the asymmetries on the Chern-Simons wave number. We predict a nonzero chiral asymmetry \Delta \mu = \mu_e_R - \mu_e_L \neq 0 in this scenario evolved down to the EWPT moment that can be used as an initial value for the Maxwellian field evolution after EWPT.

Particle-, nuclear- and atomic-physics aspects of rare weak decays of nuclei

Neutrinoless double-beta (0νββ) decay of nuclei is a process that requires the neutrino to be a massive Majorana particle and thus cannot proceed in the standard model of electro-weak interactions. The 0νββ decay takes place in atomic nuclei where it can be observed, at least in principle, by underground neutrino experiments. This work touches a special topic of the 0νββ decay, namely the emerging field of experimental and theoretical studies of the resonant neutrinoless double electron-capture decay of an atomic nucleus.

Physics of Nuclear Processes Triggered by the Interplay of Strong and Weak Interactions

Neutrinoless double beta (0νββ) decay of nuclei is a process that requires the neutrino to be a massive Majorana particle and thus cannot proceed in the standard model of electro-weak interactions. Recent results of the neutrino-oscillation experiments have produced accurate information on the mixing of neutrinos and their squared mass differences. The 0νββ decay takes place in atomic nuclei where it can be observed, at least in principle, by underground neutrino experiments. The information about the weak-interaction observables, like the neutrino mass, has to be filtered from the data through the nuclear matrix elements (NMEs). In this article recent work of the Jyväskylä group on the NMEs related to double beta decays is reviewed. This work concerns (1) the relevance to neutrinoless double beta decay of occupancies of single-particle orbitals close to the Fermi surface and (2) an example of the resonant neutrinoless double electron-capture decay of an atomic nucleus.

Dynamical symmetry breaking in models with strong Yukawa interactions

Dynamical symmetry breaking in models with strong Yukawa interactionsThe primary aim of this paper is to explore the possibility of spontaneous symmetry breaking by strong Yukawa dynamics. Technically, the symmetry is assumed to be broken by formation of symmetry-breaking parts of both the scalar and the fermion propagators, rather than by the scalar vacuum expectation values. The idea is first introduced on an example of a toy model with the underlying symmetry being an Abelian one and later applied to a realistic model of electroweak interaction. In addition, the paper also deals with some more general, model-independent issues, applicable not only to the discussed model of strong Yukawa dynamics, but to a wider class of models with dynamical mass generation. First of these issues is the problem of fermion flavor mixing in the presence of fermion self-energies with a general momentum dependence. It is in particular shown how to define the Cabibbo-Kobayashi-Maskawa matrix in such models and argued that it can come out in principle non-unitary. Second issue is the problem of calculating the gauge boson masses when the symmetry is broken by fermion self-energies. On top of deriving the formula for the gauge boson mass matrix we also find corrections to the related Pagels-Stokar formula.

Charged nontopological soliton of the SU(2) × U(1) gauge model

The SU(2) × U(1) gauge model that is the bosonic sector of the Standard Model of electroweak interactions is considered. The existence of electrically charged nontopological solitons is shown to be possible in this model. Some properties of a charged nontopological soliton are investigated. Asymptotic expressions are derived for the soliton radius, energy, and phase frequency in the thin-wall regime by the method of trial functions. Numerical solutions of the model field equations corresponding to electrically charged non-topological solitions have been obtained. The dependences of the soliton energy and charge on phase frequency are given for several model parameters. It follows from the data obtained that there exists a domain of parameters in which a charged nontopological soliton is stable to the transition to a plane-wave field configuration.

Symmetry group of massive Yang–Mills theories without Higgs and their quantization

We analyze the symmetry group of massive Yang–Mills theories and their quantization strongly motivated by an already proposed alternative to the standard model of electroweak interactions without Higgs. In these models the mass generation of the intermediate vector bosons is based on a non-Abelian Stueckelberg mechanism, where the dynamics of the Goldstone-like bosons is addressed by a partial-trace nonlinear-sigma piece of the Lagrangian. In spite of the high nonlinearity of the scalar sector, the existence of an infinite number of symmetries, extending the traditional gauge group, allows us to sketch a group-theoretical quantization algorithm specially suited to nonlinear systems, which departs from usual canonical quantization. On the quantum representation space of this extended symmetry group, a quantum Hamiltonian preserving the representation can be given, whose classical analog reproduces the equations of motion.