Model Of Electroweak Interactions Research Articles

Probing quantum decoherence at Belle II and LHCb

With the advent of Belle II and the LHCb upgrade, the precision measurements of various B-Physics observables are on cards. This holds significant potential for delving into physics beyond the standard model of electroweak interactions. These measurements can also serve as means to establish limits on phenomena occurring at much finer length scales, such as quantum decoherence, which may arise due to potential discreteness in space-time or non-trivial topological effects. In this work, we set up the formalism to investigate the impact of quantum decoherence on several potential observables in B meson systems. The approach employs the trace-preserving Kraus operator formalism, extending unitary evolution to non-unitary dynamics while maintaining complete positivity. In this formalism, the decoherence effects are parametrized in terms of a single parameter. Through the analysis of purely leptonic, semileptonic, and non-leptonic decays of B mesons, we identify observables that could, in principle, be influenced by decoherence. The theoretical expressions are provided without neglecting the impact of decay width difference (∆Γ) and CP violation in mixing. Considering that many of these observables can be measured with high precision using the abundant data collected by LHCb and Belle II, our formalism can be applied to establish constraints on the decoherence parameter through multiple decay channels. This offers an alternative set-up for such studies, which, at present, are predominantly conducted in the neutrino sector.

On the Breaking of the U(1) Peccei–Quinn Symmetry and Its Implications for Neutrino and Dark Matter Physics

The Standard Model of electroweak interactions is based on the fundamental SU(2)weak × U(1)elect representation. It assumes massless neutrinos and purely left-handed massive W± and Z0 bosons to which one should add the massless photon. The existence, verified experimentally, of neutrino oscillations poses a challenge to this scheme, since the oscillations take place between at least three massive neutrinos belonging to a mass hierarchy still to be determined. One should also take into account the possible existence of sterile neutrino species. In a somehow different context, the fundamental nature of the strong interaction component of the forces in nature is described by the, until now, extremely successful representation based on the SU(3)strong group which, together with the confining rule, give a description of massive hadrons in terms of quarks and gluons. To this is added the minimal U(1) Higgs group to give mass to the otherwise massless generators. This representation may also be challenged by the existence of both dark matter and dark energy, of still unknown composition. In this note, we shall discuss a possible connection between these questions, namely the need to extend the SU(3)strong × SU(2)weak × U(1)elect to account for massive neutrinos and dark matter. The main point of it is related to the role of axions, as postulated by Roberto Peccei and Helen Quinn. The existence of neutral pseudo-scalar bosons, that is, the axions, has been proposed long ago by Peccei and Quinn to explain the suppression of the electric dipole moment of the neutron. The associated U(1)PQ symmetry breaks at very high energy, and it guarantees that the interaction of other particles with axions is very weak. We shall review the axion properties in connection with the apparently different contexts of neutrino and dark matter physics.

The Neutrino Mass Problem: From Double Beta Decay to Cosmology

The neutrino is perhaps the most elusive member of the particle zoo. The questions about its nature, namely: Dirac or Majorana, the value of its mass and the interactions with other particles, the number of its components including sterile species, are long standing ones and still remain to a large extent without conclusive answers. From the side of the nuclear structure and nuclear reactions, both theories and experiments, the need to elucidate these questions has, and still has, prompt crucial developments in the fields of double beta decay, double charge exchange and neutrino induced reactions. The measurements of neutrino flavor oscillation parameters contribute largely to restrict models with massless neutrinos. From the particle physics side, the possibilities to extend the standard model of electroweak interactions to incorporate a right-handed sector of the electroweak Lagrangian are directly linked to the adopted neutrino model. Here, I would like to address another aspect of the problem by asking the question of the neutrino mass mechanism in the cosmological context, and particularly about dark matter.

Impact of b → c measurements on [formula omitted] decay in U1 leptoquark model

The measurements of several lepton flavor universality (LFU) violating observables in the decays induced by the quark level transition b→cτν¯ provide an inkling of plausible physics beyond the standard model of electroweak interactions. Such new physics would also impact other sectors. In this work, we estimate the leverage of new physics in b→cτν¯ on Λb→pτν¯ decay in the context of U1 leptoquark model. In this model, the new physics couplings in b→uτν¯ transition can be written in terms of b→cτν¯ couplings and hence the extent of allowed new physics in Λb→pτν¯ would be determined by b→cτν¯ transition. Using the new physics parameter space obtained by performing a fit to all b→cτν¯ data, we obtain predictions of several Λb→pτν¯ observables. We find that the current b→cτν¯ data allows two times of magnitude enhancement in the branching ratio as well as in the LFU ratio. The other observables such as convexity parameter, lepton forward-backward asymmetry, longitudinal polarization of final state baryon and tau lepton are consistent with the SM value.

Daughter Higgs Boson in the Unified Composite Model

In the unified subquark model of all fundamental particles and forces, the mass of the Higgs boson in the standard model of electroweak interactions (mH) is predicted to be about 2√6 mW / 3 (where mW is the mass of the charged weak boson, W ), which agrees well with the experimental values of about 125 GeV found by the ATLAS and CMS Collaborations at the LHC in 2011. It seems to indicate that the Higgs boson is a composite of the iso-doublet spinor 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. In the unified composite model, there may appear a daughter of the Higgs boson whose mass is predicted to be 2 mW /√3, which agrees well with the experimental values of about 95 GeV for the excess events, found by the LEP experiments and recently by the CMS experiment. This agreement seems to strongly indicate not only the compositeness of the Higgs bosons but also the validity of the unified composite model of all fundamental particles and forces.

New phenomena in laser-assisted leptonic decays of the negatively charged boson W −

The majority of studies and experiments performed at electron-positron colliders over the last two decades have focused on studying W and Z weak force-carrying bosons and accurately measuring all their properties, not only because they play an important role in establishing Standard Model theory and providing an accurate test of its predictions of particle interactions, but also because they are a unique tool for probing manifestations of the new physics beyond the standard model. Therefore, it would be particularly important to discuss some of the new phenomena and changes that can arise in these bosons when their decay occurs under an external electromagnetic field. In a recent paper, we investigated the laser effect on the final products of Z boson decay and found that laser had an unprecedented effect on branching ratios. In this work and within the standard Glashow-Weinberg-Salam model of electroweak interactions, we study theoretically the leptonic decay of the W −-boson in the presence of a circularly polarized electromagnetic field and we examine the laser effect, in terms of its field strength and frequency, on the leptonic decay rate and the phenomenon of multiphoton processes. The calculations are carried out using the exact relativistic wave functions of charged particles in an electromagnetic field. It was found that the laser significantly contributed to reducing the probability of W −-boson decay. We show that the laser-assisted decay rate is equal to the laser-free one only when the famous Kroll-Watson sum rule is fulfilled. The notable effect of the laser on the leptonic decay rate was reasonably interpreted by the well-known quantum Zeno effect or by the opening of channels other than leptonic ones to decay. This work will pave the way for an upcoming one to study the hadronic decay of the W −-boson and then explore the laser effect on its lifetime and branching ratios.

Strong magnetic fields in gauge theories

The problem of photon propagation in a medium in presence of a strong magnetic field in the frame of quantum electrodynamics is discussed in the present paper, based on previous literature in this area. The breaking of the spatial symmetry by the magnetic field determine the existence of a set of basic vectors and tensors which must satisfy the gauge and CPT invariance of quantum electrodynamics. The charge symmetric and non-symmetric cases are discussed. In the second case the Faraday effect is produced. A chiral current arises, associated to a pseudovector eigenvector ofthe polarization operator (due to the breaking of the spatial symmetry by the external magnetic field), related to the so-called axial anomaly. The path integrals and functional derivation are widely used to obtain the self-energy and vertex operators, and the Dyson equations. The inadequate introduction of a chiral chemical potential in the standard model is discussed for the Weinberg-Salam model for electroweak interactions.

Accessing weak neutral-current coupling $$g_{AA}^{eq}$$ using positron and electron beams at Jefferson Lab

Low-energy neutral-current couplings arising in the Standard Model of electroweak interactions can be constrained in lepton scattering off hydrogen or a nuclear fixed target. Recent polarized electron scattering experiments at Jefferson Lab (JLab) have improved the precision in the parity-violating types of effective couplings. On the other hand, the only known way to access the parity-conserving counterparts is to compare scattering cross sections between a lepton and an anti-lepton beam. We review the current knowledge of both types of couplings and how to constrain them. We also present exploratory calculations for a possible measurement of $g_{AA}^{eq}$ using the planned SoLID spectrometer combined with a possible positron beam at JLab.

Neutrino Charge in a Magnetized Media

In the presence of a thermal medium or an external electro-magnetic field, neutrinos can interact with photon, mediated by the corresponding charged leptons (real or virtual). The effect of a medium or an electromagnetic field is two-fold—to induce an effective νγ vertex and to modify the dispersion relations of all the particles involved to render the processes kinematically viable. It has already been noted that, in a medium, neutrinos acquire an effective charge, which in the standard model of electroweak interaction comes from the vector type vertex of weak interaction. On the other hand, in a magnetized plasma, the axial vector part also starts contributing to the effective charge of a neutrino. This contribution corresponding to the axial vector part in the interaction Lagrangian is denoted as the axial polarisation tensor. In this note, we outline the calculation of the axial polarization tensor to odd and even powers in eB. We further show its gauge invariance properties. Finally, we infer upon the zero external momentum limit of this axial polarisation tensor.

Global Evolution of the U(1) Higgs Boson: Nonlinear Stability and Uniform Energy Bounds

Relying on the hyperboloidal foliation method, we establish the nonlinear stability of the ground state of the U(1) standard model of electroweak interactions. This amounts to establishing a global-in-time theory for the initial value problem for a nonlinear wave–Klein–Gordon system that couples (Dirac, scalar, gauge) massive equations together. In particular, we investigate here the Dirac equation and study a new energy functional defined with respect to the hyperboloidal foliation of Minkowski spacetime. We provide a decay result for the Dirac equation which is uniform in the mass coefficient and thus allows for the Dirac mass coefficient to be arbitrarily small. Furthermore, we establish energy bounds for the Higgs fields and gauge bosons that are uniform with respect to the hyperboloidal time variable.

Operation Features of the Electronic Circuit of the Warm Liquid Tetramethylsilane (TMS) Detector

It is urgent to use a “warm liquid” TMS in large massive calorimeters (with a volume of several hundred liters). This direction in modern nuclear physics is referred to as “non-accelerator” experiments with low-background detectors. Such experiments are associated with the solution of most important problems to understand the Universe structure and search for new particles. These are the well-known problems for searching “dark matter” in the form of new weakly interacting particles, i.e., wimps, observations of coherent scattering of reactor neutrinos. Using this experiment, the standard model of electroweak interactions can be tested. The fully developed fabrication technology of large amounts of “warm liquid” ТМS (in collaboration with the State Research Institute of Chemistry and Technology of Organoelement Compounds) makes it possible to perform such experiments.

Extension of the standard model of electroweak interaction and Dark Matter in the tangent bundle geometry

A generalized theory of electroweak interaction is developed based on the underlying geometrical structure of the tangent bundle with symmetries arising from transformations of tangent vectors along the fiber axis at a fixed spacetime point given by the SO(3,1) group. Electroweak interaction beyond the standard model (SM) is described by the little groups SU(2)otimes E^{c}(2) (E^{c}(2) is the central extended Euclidian group) which includes the group SU(2)otimes U(1) as a limit case. In addition to isospin and hypercharge, two additional quantum numbers arise which explain the existence of families in the SM. The connection coefficients yield the SM gauge potentials but also hypothetical gauge bosons and other hypothetical particles as a Higgs family as well as candidate Dark Matter particles are predicted. Several important consequences for the interaction between dark fermions, dark scalars or dark vector gauge bosons with each other and with SM Higgs and Z-bosons are described.

Brans–Dicke gravity: From Higgs physics to (dynamical) dark energy

The Higgs mechanism is one of the central pieces of the Standard Model of electroweak interactions and thanks to it we can generate the masses of the elementary particles. Its fundamental origin is nonetheless unknown. Furthermore, in order to preserve renormalizability, we have to break the gauge symmetry spontaneously, which leads to a huge induced cosmological constant incompatible with observations. It turns out that in the context of generalized Brans–Dicke theories of gravity, the Higgs potential structure can be motivated from solutions of the field equations which carry harmless cosmological vacuum energy. In addition, the late-time cosmic evolution effectively appears like a universe filled with mildly evolving dynamical dark energy mimicking quintessence or phantom dark energy.

Local scale-invariance breaking in the standard model by two-measure theory

We introduce Weyl's scale invariance as additional local symmetry in the standard model of electroweak interactions. Under this, the gauge symmetry of the standard model now is $SU(3)\ifmmode\times\else\texttimes\fi{}SU(2)\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0ex}{0ex}}U(1)\ifmmode\times\else\texttimes\fi{}\stackrel{\texttildelow{}}{U}(1)$, where $\stackrel{\texttildelow{}}{U}(1)$ is for local scale invariance, and its gauge boson is called the Weylon. Also introduced are two new scalars ${\ensuremath{\sigma}}_{1}$ and ${\ensuremath{\sigma}}_{2}$ with the common scaling weight $\ensuremath{-}1$. The mechanism for spontaneous breaking of scale invariance is invoked by coupling ${\ensuremath{\sigma}}_{2}$ to a metric-independent measure defined in terms of an additional four scalars ${\ensuremath{\phi}}^{I}(I=1,2,3,4)$. Weyl's scale invariance is now implemented by combining it with internal diffeomorphisms of the four scalars ${\ensuremath{\phi}}^{i}$. We show that once local scale invariance is broken, the phenomenon (a) generates Newton's gravitational constant ${G}_{N}$ and (b) triggers spontaneous symmetry breaking in the conventional manner resulting in masses for the conventional fermions and bosons. The scale at which Weyl's scale symmetry breaks is of order Planck mass. If right-handed neutrinos are also introduced, their absence at present energy scales is attributed to their mass being tied to the scale at which scale invariance breaks. New $C$- and $CP$-violating effects can also be induced by mixing the Weylon with the hypercharge gauge boson of the standard model.

Search for creation of electrons in lab

We examine the physics motivations to search for lepton number violations in the laboratory, in particular by studying the important nuclear transition called neutrinoless double beta decay, which consists in the creation of a pair of electrons. We address some major shortcomings of the Standard Model of electroweak interactions, arguing that most of them can be solved simply within extended models with Majorana neutrinos. At the same time, we discuss the difficulties of obtaining precise predictions for the neutrinoless double beta decay rate and strengthen the case of probing Majorana neutrino masses of about 10 meV.

3a-B-5 非可換幾何学に基づく左右対称電弱模型

3a-B-5 非可換幾何学に基づく左右対称電弱模型

The Weinberg‐Salam Model of Electroweak Interactions: Ingenious Discovery or Lucky Hunch?

AbstractThis contribution looks back at the papers published fifty years ago by Abdus Salam and Steven Weinberg, which are today regarded as marking the coming‐to‐be of the Weinberg‐Salam model of electroweak interactions. Despite their present fame, at the time of their publication the papers went largely unnoticed. Reconstructing the historical context from which they emerged will show how, against the traditional image of theoretical physicists as “lone geniuses,” the Weinberg‐Salam model actually came to be thanks to the interplay of many different actors and ideas.

Precision theoretical analysis of neutron radiative beta decay

In the Standard Model of electroweak interactions and in the tree--approximation we calculate the rate and branching ratio of the neutron radiative beta decay with one-real photon emission by taking into account the contributions of the weak magnetism and proton recoil to order 1/m_p of the large proton mass m_p expansion. We find that the obtained contributions of the weak magnetism and proton recoil increase the rate and branching ratio of the neutron radiative beta decay by about 0.70%. This is large compared with the contribution of the weak magnetism and proton recoil of about 0.16% to the rate of the neutron beta decay, calculated in Phys. Rev. D88, 073002 (2013).

The evolution of gauge couplings and the Weinberg angle in 5 dimensions for an SU(3) gauge group

We test in a simplified 5-dimensional model with SU(3) gauge symmetry, the evolution equations of the gauge couplings of a model containing bulk fields, gauge fields and one pair of fermions. In this model we assume that the fermion doublet and two singlet fields are located at fixed points of the extra-dimension compactified on an S1/Z2 orbifold. The gauge coupling evolution is derived at one-loop in 5-dimensions, for the gauge group G = SU(3), and used to test the impact on lower energy observables, in particular the Weinberg angle. The gauge bosons and the Higgs field arise from the gauge bosons in 5 dimensions, as in a gauge- Higgs model. The model is used as a testing ground as it is not a complete and realistic model for electroweak interactions.

Higgs potential from extended Brans–Dicke theory and the time-evolution of the fundamental constants

Despite the enormous significance of the Higgs potential in the context of the standard model of electroweak interactions and in grand unified theories, its ultimate origin is fundamentally unknown and must be introduced by hand in accordance with the underlying gauge symmetry and the requirement of renormalizability. Here we propose a more physical motivation for the structure of the Higgs potential, which we derive from a generalized Brans–Dicke (BD) theory containing two interacting scalar fields. One of these fields is coupled to curvature as in the BD formulation, whereas the other is coupled to gravity both derivatively and non-derivatively through the curvature scalar and the Ricci tensor. By requiring that the cosmological solutions of the model are consistent with observations, we show that the effective scalar field potential adopts the Higgs potential form with a mildly time-evolving vacuum expectation value. This residual vacuum dynamics could be responsible for the possible time variation of the fundamental constants, and is reminiscent of former Bjorken’s ideas on the cosmological constant problem.