Electroweak Model Research Articles

Erratum: One-loop self-energies in the electroweak model with a nonlinearly realized gauge group [Phys. Rev. D79, 125028 (2009)

Erratum: One-loop self-energies in the electroweak model with a nonlinearly realized gauge group [Phys. Rev. D<b>79</b>, 125028 (2009)

Rare interactions of neutrinos with matter as contraction of the Electroweak Model

The modification of the electroweak model with contracted gauge group SU(2; ϵ) × U(1) is suggested. The field space of the model is fibered under contraction in such a way that neutrino fields are in the fiber. Properties of the fibered field space are understood in context of semi-Riemannian geometry. Contraction of gauge group is connected with the limit properties of the cross-section for interactions of neutrinos with matter, when neutrinos energy tends to zero. For small contraction parameter this model explain already at the level of classical gauge fields why neutrinos so rarely interact with anything and why their cross-section with matter increase with energy. Small contraction parameter is connected with the universal Fermi constant of weak interactions and neutrino energy as The modified model need be considered at low energies much less then gauge bosons masses.

Searches for supersymmetry with the ATLAS detector using final states with two leptons and missing transverse momentum in [formula omitted] proton–proton collisions

Results of three searches are presented for the production of supersymmetric particles decaying into final states with missing transverse momentum and exactly two isolated leptons, e or μ. The analysis uses a data sample collected during the first half of 2011 that corresponds to a total integrated luminosity of 1 fb−1 of s=7 TeV proton–proton collisions recorded with the ATLAS detector at the Large Hadron Collider. Opposite-sign and same-sign dilepton events are separately studied, with no deviations from the Standard Model expectation observed. Additionally, in opposite-sign events, a search is made for an excess of same-flavour over different-flavour lepton pairs. Effective production cross sections in excess of 9.9 fb for opposite-sign events containing supersymmetric particles with missing transverse momentum greater than 250 GeV are excluded at 95% CL. For same-sign events containing supersymmetric particles with missing transverse momentum greater than 100 GeV, effective production cross sections in excess of 14.8 fb are excluded at 95% CL. The latter limit is interpreted in a simplified electroweak gaugino production model excluding chargino masses up to 200 GeV, under the assumption that slepton decay is dominant.

Primary Feynman rules to calculate the ∊-dimensional integrand of any 1-loop amplitude

When using dimensional regularization/reduction the epsilon-dimensional numerator of the 1-loop Feynman diagrams gives rise to rational contributions. I list the set of fundamental rules that allow the extraction of such terms at the integrand level in any theory containing scalars, vectors and fermions, such as the electroweak standard model, QCD and SUSY.

On invariants of quark and lepton mass matrices in the Standard Model

In this article I present the motivation for introducing the invariant functions of mass matrices, based on my own work, and give some examples. Since their introduction in 1985, in the framework of the standard electroweak model, they have been used by many authors. Some authors have gone further along this path and have studied the extensions of this concept to frameworks beyond the standard model. I hope, in the near future, to give a more detailed account of this subject, including recent developments.

Z′boson fromSU(6)×SU(2)hgrand unified theory, CDFWjjexcess and Higgs boson mass bound

A general electroweak scale $Z'$ is applied in a supersymmetric SU(6)$\timesSU(2)_h$ grand unification model, to have a $\Z_6$ for the hexality. We briefly show that there cannot exist any baryonic U(1)$'_B$ in any subgroup of E$_6$. Any effect that requires sizable $Z'$ couplings to quarks like the reported Wjj anomaly of CDF, if observed, implies a substantial $Z'$ coupling to leptons or Higgs doublets. The kinetic mixing considered in a supersymmetric model from E$_6$ is restricted by the gauge coupling unification and neutrino mixing. The mass of $Z'$ is strongly constrained by the electroweak $\rho_0$ parameter. We conclude that $Z'$ mass much above 10 TeV is favored by considering the neutrino mixing and proton decay constraint in supersymmetric models. In this sense, the CDF $Wjj$ anomaly cannot be fitted to any electroweak model descending from E$_6$. Furthermore, if $Z'$ is found at several hundred GeV, any grand unification group embedded in E$_6$ such as SU(6)$\times$SU(2), SO(10), SU(5)$\times$U(1), SU(5), SU(4)$\times$SU(4), and SU(3)$^3$, needs fine-tuned gauge couplings. We also discuss the U(1)$'$ effect on the tree level mass of the lightest MSSM Higgs boson.

Electric dipole moments: Flavor-diagonal CP violation

Abstract Searches for permanent electric dipole moments of particles, nuclei, atoms and molecules offer an extraordinary discovery potential to new mechanisms of CP violation beyond those incorporated in the standard electroweak model. The electric dipole moments induced by speculative scenarios, on different physical systems, require a complementary approach to pave the way to the fundamental CP-violating mechanisms. New avenues presently being explored in order to improve the experimental sensitivities include projects that consider the trapping of neutral particles, the confinement of charged particles in storage rings as well as the use of radioactive nuclei.

Symmetry Tests in Nuclear Beta Decay

Precision measurements in nuclear β decay provide sensitive means to test the structure of the standard electroweak model; they also allow the determination of fundamental properties in processes that involve the lightest quarks. The primary aim of such tests is to find deviations from the Standard Model predictions that may indicate new physics. We review here the status of precision measurements in nuclear β decay, including selected experiments in neutron decay, and discuss recent results and developments. Among these developments are the consideration of nuclear mirror transitions as a new window in which to test the unitarity condition of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix, measurements of angular correlation observables to search for exotic couplings, and tests of discrete symmetries.

Minimal 3-3-1 model with only two Higgs triplets

The simplest non-Abelian gauge extension of the electroweak standard model, the $SU(3{)}_{c}\ensuremath{\bigotimes}SU(3{)}_{L}\ensuremath{\bigotimes}U(1{)}_{N}$, known as the 3-3-1 model, has a minimal version which demands the least possible fermionic content to account for the whole established phenomenology for the well-known particles and interactions. Nevertheless, in its original form the minimal 3-3-1 model was proposed with a set of three scalar triplets and one sextet in order to yield the spontaneous breaking of the gauge symmetry and generate the observed fermion masses. Such a huge scalar sector turns the task of clearly identifying the physical scalar spectrum into a clumsy labor. It not only adds an obstacle for the development of its phenomenology, but implies a scalar potential plagued with new free coupling constants. In this work, we show that the framework of the minimal 3-3-1 model can be built with only two scalar triplets, but still triggering the desired pattern of spontaneous symmetry breaking and generating the correct fermion masses. We present the exact physical spectrum and also show all the interactions involving the scalars, obtaining a neat minimal 3-3-1 model far more suited for phenomenological studies at the current Large Hadron Collider.

The neutron and its role in cosmology and particle physics

Experiments with cold and ultracold neutrons have reached a level of precision such that problems far beyond the scale of the present standard model of particle physics become accessible to experimental investigation. Because of the close links between particle physics and cosmology, these studies also permit a deep look into the very first instances of our Universe. First addressed in this article, in both theory and experiment, is the problem of baryogenesis, the mechanism behind the evident dominance of matter over antimatter in the Universe. The question of how baryogenesis could have happened is open to experimental tests, and it turns out that this problem can be curbed by the very stringent limits on an electric dipole moment of the neutron, a quantity that also has deep implications for particle physics. Then the recent spectacular observation of neutron quantization in the Earth's gravitational field and of resonance transitions between such gravitational energy states is discussed. These measurements, together with new evaluations of neutron scattering data, set new constraints on deviations from Newton's gravitational law at the picometer scale. Such deviations are predicted in modern theories with extra dimensions that propose unification of the Planck scale with the scale of the standard model. These experiments start closing the remaining ``axion window'' on new spin-dependent forces in the submillimeter range. Another main topic is the weak-interaction parameters in various fields of physics and astrophysics that must all be derived from measured neutron-decay data. Up until now, about 10 different neutron-decay observables have been measured, much more than needed in the electroweak standard model. This allows various precise tests for new physics beyond the standard model, competing with or surpassing similar tests at high energy. The review ends with a discussion of neutron and nuclear data required in the synthesis of the elements during the ``first three minutes'' and later on in stellar nucleosynthesis.

Neutrino masses and the scalar sector of aB−Lextension of the standard model

We consider an electroweak model based on the gauge symmetry SU(2)_L X U(1)_Y' X U(1)_B-L which has right-handed neutrinos with different exotic B-L quantum numbers. Because of this particular feature we are able to write Yukawa terms, and right-handed neutrino mass terms, with scalar fields that can develop vacuum expectation values belonging to different energy scales. We make a detailed study of the scalar and the Yukawa neutrino sectors to show that this model is compatible with the observed solar and atmospheric neutrino mass scales and the tribimaximal mixing matrix.We also show that there are dark matter candidates if a Z_2 symmetry is included.

ZB−L′phenomenology at the LHC

We study the ${Z}^{\ensuremath{'}}$ phenomenology for two extensions of the electroweak standard model (SM) which have an extra $U(1{)}_{B\ensuremath{-}L}$ gauge factor. We show the capabilities of the LHC in distinguishing the signals coming from these two extensions and both of them from the SM background. In order to compare the behavior of these $B\ensuremath{-}L$ models we consider the reaction $p+p\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}+{\ensuremath{\mu}}^{\ensuremath{-}}+X$ and compute some observables as the total cross sections, number of events, forward-backward asymmetry, final particle distributions like rapidity, transverse momentum, and dimuon invariant mass, for two LHC regimes: $\sqrt{s}(\mathcal{L})=7\text{ }\text{ }\mathrm{TeV}$ ($1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$) and 14 TeV ($100\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$) for ${M}_{{Z}^{\ensuremath{'}}}=1000\text{ }\text{ }\mathrm{GeV}$ and 1500 GeV. We show that by using appropriate kinematic cuts some of the observables considered here, we are able to extract different properties of the ${Z}^{\ensuremath{'}}$ boson, and hence to provide information about to which $B\ensuremath{-}L$ model it belongs to.

Extra dimensions as a source of the electroweak model

The Higgs boson of the Standard model is described by a set of off-diagonal components of the multidimensional metric tensor, as well as the gauge fields. In the low-energy limit, the basic properties of the Higgs boson are reproduced, including the shape of the potential and interactions with the gauge fields of the electroweak part of the Standard model.

Erratum to: Revisiting the global electroweak fit of the Standard Model and beyond with Gfitter

The global fit of the Standard Model to electroweak precision data, routinely performed by the LEP electroweak working group and others, demonstrated impressively the predictive power of electroweak unification and quantum loop corrections. We have revisited this fit in view of (i) the development of the new generic fitting package Gfitter, (ii) the insertion of constraints from direct Higgs searches at LEP and the Tevatron, and (iii) a more thorough statistical interpretation of the results. Gfitter is a modular fitting toolkit, which features predictive theoretical models as independent plugins, and a statistical analysis of the fit results using toy Monte Carlo techniques. The state-of-the-art electroweak Standard Model is fully implemented, as well as generic extensions to it. This paper introduces the Gfitter project, and presents state-of-the-art results for the global electroweak fit in the Standard Model, and for a model with an extended Higgs sector (2HDM). Numerical and graphical results for fits with and without including the constraints from the direct Higgs searches at LEP and Tevatron are given. Perspectives for future colliders are analysed and discussed. Including the direct Higgs searches, we find M_H=(116.4 +18.3 -1.3) GeV, and the 2sigma and 3sigma allowed regions [114,145] GeV and [[113,168] and [180,225]] GeV, respectively. For the strong coupling strength at fourth perturbative order we obtain alpha_S(M_Z)=0.1193 +0.0028 -0.0027(exp) +- 0.0001(theo). Finally, for the mass of the top quark, excluding the direct measurements, we find m_t=(178.2 +9.8 -4.2) GeV. In the 2HDM we exclude a charged-Higgs mass below 240 GeV at 95% confidence level. This limit increases towards larger tan(beta), where e.g., M_H+-<780 GeV is excluded for tan(beta)=70.

Generalized holographic electroweak symmetry breaking models and the possibility of negativeS^

Within an AdS/CFT inspired model of electroweak symmetry breaking, the effects of various boundary terms and modifications to the background are studied. The effect on the $\stackrel{^}{S}$ precision parameter is discussed, with particular attention to its sign and whether the theory is unitary when $\stackrel{^}{S}&lt;0$. Connections between the various possible AdS slice models of symmetry breaking are discussed.

Constraining nonstandard neutrino interactions with electrons

We update the phenomenological constraints of the nonstandard neutrino interactions (NSNI) with electrons including in the analysis, for the first time, data from LAMPF, Krasnoyarsk, and the latest Texono observations. We assume that NSNI modify the cross section of elastic scattering of (anti)neutrinos off electrons, using reactor and accelerator data, and the cross section of the electron-positron annihilation, using the four LEP experiments, in particular, new data from DELPHI. We find more restrictive allowed regions for the NSNI parameters: $\ensuremath{-}0.11l{\ensuremath{\epsilon}}_{ee}^{eR}l0.05$ and $\ensuremath{-}0.02l{\ensuremath{\epsilon}}_{ee}^{eL}l0.09$ (90% C.L.). We also recalculate the parameters of tauonic flavor obtaining $\ensuremath{-}0.35l{\ensuremath{\epsilon}}_{\ensuremath{\tau}\ensuremath{\tau}}^{eR}l0.50$ and $\ensuremath{-}0.51l{\ensuremath{\epsilon}}_{\ensuremath{\tau}\ensuremath{\tau}}^{eL}l0.34$ (90% C.L.). Although more severe than the limits already present in the literature, our results indicate that NSNI are allowed by the present data as a subleading effect, and the standard electroweak model continues consistent with the experimental panorama at 90% C.L. Further improvement on this picture will deserve a lot of engagement of upcoming experiments.

STRATEGIES TO LINK TINY NEUTRINO MASSES WITH HUGE MISSING MASS OF THE UNIVERSE

With the start of the LHC, interest in electroweak scale models for the neutrino mass has grown. In this paper, we review two specific models that simultaneously explain neutrino masses and provide a suitable DM candidate. We discuss the implications of these models for various observations and experiments including the LHC, Lepton Flavor Violating (LFV) rare decays, direct and indirect dark matter searches and kaon decay.

Limiting case of modified electroweak model for contracted gauge group

The modification of the Electroweak Model with 3-dimensional spherical geometry in the matter fields space is suggested. The Lagrangian of this model is given by the sum of the free (without any potential term) matter fields Lagrangian and the standard gauge fields Lagrangian. The vector boson masses are generated by transformation of this Lagrangian from Cartesian coordinates to coordinates on the sphere S 3. The limiting case of the bosonic part of the modified model, which corresponds to the contracted gauge group SU(2; j) × U(1) is discussed. Within framework of the limit model Z boson and electromagnetic fields can be regarded as external ones with respect to W-boson fields in the sence that W-boson fields do not effect on these external fields. The masses of all particles of the Electroweak Model remain the same, but field interactions in contracted model are more simple as compared with the standard Electroweak Model.

Higgsless Electroweak Model and contraction of gauge group

A modified formulation of the Electroweak Model with 3-dimensional spherical geometry in the target space is suggested. The {\it free} Lagrangian in the spherical field space along with the standard gauge field Lagrangian form the full Higgsless Lagrangian of the model, whose second order terms reproduce the same experimentally verified fields with the same masses as the Standard Electroweak Model. The vector bosons masses are automatically generated, so there is no need in special mechanism of spontaneous symmetry breaking. The limiting case of the modified Higgsless Electroweak Model, which corresponds to the contracted gauge group $SU(2;j)\times U(1)$ is discussed. Within framework of the limit model Z-boson, electromagnetic and electron fields are interpreted as an external ones with respect to W-bosons and neutrino fields. The W-bosons and neutrino fields do not effect on these external fields. The masses of all particles remain the same, but the field interactions in contracted model are more simple as compared with the standard Electroweak Model due to nullification of some terms.

Ultraviolet complete electroweak model without a Higgs particle

An electroweak model with running coupling constants described by an energy dependent entire function is utraviolet complete and avoids unitarity violations for energies above 1 TeV. The action contains no physical scalar fields and no Higgs particle and the physical electroweak model fields are local and satisfy microcausality. The W and Z masses are compatible with a symmetry breaking SU(2)L×U(1)Y $ \rightarrow$ U(1)em , which retains a massless photon. The vertex couplings possess an energy scale $ \Lambda_{W}^{}$ > 1 TeV predicting scattering amplitudes that can be tested at the LHC.