Search results for "Electroweak"
showing 10 items of 744 documents
Baryogenesis and gravity waves from a UV-completed electroweak phase transition
2021
We study gravity wave production and baryogenesis at the electroweak phase transition, in a real singlet scalar extension of the Standard Model, including vector-like top partners to generate the CP violation needed for electroweak baryogenesis (EWBG). The singlet makes the phase transition strongly first-order through its coupling to the Higgs boson, and it spontaneously breaks CP invariance through a dimension-5 contribution to the top quark mass term, generated by integrating out the heavy top quark partners. We improve on previous studies by incorporating updated transport equations, compatible with large bubble wall velocities. The wall speed and thickness are computed directly from th…
Hadronic τ Decays as New Physics Probes in the LHC Era
2019
We analyze the sensitivity of hadronic tau decays to non-standard interactions within the model-independent framework of the Standard Model Effective Field Theory (SMEFT). Both exclusive and inclusive decays are studied, using the latest lattice data and QCD dispersion relations. We show that there are enough theoretically clean channels to disentangle all the effective couplings contributing to these decays, with the $\tau \to \pi\pi\nu_\tau$ channel representing an unexpected powerful New Physics probe. We find that the ratios of non-standard couplings to the Fermi constant are bound at the sub-percent level. These bounds are complementary to the ones from electroweak precision observable…
Weak charge and weak radius of C12
2020
We present a feasibility study of a simultaneous subpercent extraction of the weak charge and the weak radius of the $^{12}\mathrm{C}$ nucleus using parity-violating electron scattering, based on a largely model-independent assessment of the uncertainties. The corresponding measurement is considered to be carried out at the future MESA facility in Mainz with ${E}_{\mathrm{beam}}=155\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$. We find that a combination of a 0.3% precise measurement of the parity-violating asymmetry at forward angles with a 10% measurement at backward angles will allow to determine the weak charge and the weak radius of $^{12}\mathrm{C}$ with 0.4% and 0.5% precision, respectiv…
The neutrino charge radius is a physical observable
2004
We present a method which allows, at least in principle, the direct extraction of the gauge-invariant and process-independent neutrino charge radius (NCR) from experiments. Under special kinematic conditions, the judicious combination of neutrino and anti-neutrino forward differential cross-sections allows the exclusion of all target-dependent contributions, such as gauge-independent box-graphs, not related to the NCR. We show that the remaining contributions contain universal, renormalization group invariant combinations, such as the electroweak effective charge and the running mixing angle, which must be also separated out. By considering the appropriate number of independent experiments …
Anomalous top magnetic couplings
2012
The real and imaginary parts of the one-loop electroweak contributions to the left and right tensorial anomalous couplings of the tbW vertex in the Standard Model (SM) are computed.
Measurement of the Parity Violation in Quasi-Elastic Electroweak Electron-Scattering from 9Be
1986
In the energy range of about 300 MeV, available at the Mainz- Linac, quasi-elastic scattering dominates the total cross section at backward scattering angles. This process can therefore be detected efficiently by a gas Cerenkov-counter with large solid angle. This is a prerequisit for experiments on parity violation due to the very small asymmetry effect being of the order of 1|10-5 at these energies [1]. The counting system built, consists of 12 elliptical mirrors, imaging the Cerenkov photons seen in target direction onto photomultipliers. The mirrors cover the full azimuth for polar angles 115°≦ϑ≦145°, thus covering 20% of 4π (Fig. 1). The detector has been proved to yield a statistical …
The effective neutrino charge radius
2003
It is shown that at one-loop order a neutrino charge radius (NCR) may be defined, which is ultraviolet finite, does not depend on the gauge-fixing parameter, nor on properties of the target other than its electric charge. This is accomplished through the systematic decomposition of physical amplitudes into effective self-energies, vertices, and boxes, which separately respect electroweak gauge invariance. In this way the NCR stems solely from an effective proper photon-neutrino one-loop vertex, which satisfies a naive, QED-like Ward identity. The NCR so defined may be extracted from experiment, at least in principle, by expressing a set of experimental electron-neutrino cross-sections in te…
Deconfinement vs. chiral symmetry and higher representation matter
2012
The interplay of deconfinement and chiral symmetry restoration are considered in terms of effective theories. We generalize the earlier model studies by considering fermions in higher representations, and study the finite temperature phase diagrams of SU(2) and SU(3) gauge theories with two fermion flavors in fundamental, adjoint or two-index symmetric representations. We discuss our results in relation to recent lattice simulations on these theories and outline possible applications in the context of dynamical electroweak symmetry breaking.
Measurements of Multi-boson production, Trilinear and Quartic Gauge Couplings with the ATLAS detector
2016
The ATLAS collaboration has carried a set of measurements that provide stringent tests of the electroweak sector of Standard Model, specifically on di- and multi-boson production cross sections and on triple and quartic gauge-boson couplings. Such measurements include cross sections for WV (V=W or Z) production in the leptonic or semileptonic channels, the production of a W or Z boson in association with photons, a Z boson in the vector-boson fusion channel and two same-charge W bosons in the vector-boson scattering channel. These measurements are compared to (N)NLO predictions of the Standard Model and provide model-independent constraints on new physics, by setting limits on anomalous gau…
Composite Higgs bosons from neutrino condensates in an inverted see-saw scenario
2020
We present a realization of the idea that the Higgs boson is mainly a bound state of neutrinos induced by strong four-fermion interactions. The conflicts of this idea with the measured values of the top quark and Higgs boson masses are overcome by introducing, in addition to the right-handed neutrino, a new fermion singlet, which, at low energies, implements the inverse see-saw mechanism. The singlet fermions also develop a scalar bound state which mixes with the Higgs boson. This allows us to obtain a small Higgs boson mass even if the couplings are large, as required in composite scalar scenarios. The model gives the correct masses for the top quark and Higgs boson for compositeness scale…