Search results for "electroweak interaction"
showing 10 items of 358 documents
One-loop calculation of the oblique S parameter in higgsless electroweak models
2012
We present a one-loop calculation of the oblique S parameter within Higgsless models of electroweak symmetry breaking and analyze the phenomenological implications of the available electroweak precision data. We use the most general effective Lagrangian with at most two derivatives, implementing the chiral symmetry breaking SU(2)_L x SU(2)_R -> SU(2)_{L+R} with Goldstones, gauge bosons and one multiplet of vector and axial-vector massive resonance states. Using the dispersive representation of Peskin and Takeuchi and imposing the short-distance constraints dictated by the operator product expansion, we obtain S at the NLO in terms of a few resonance parameters. In asymptotically-free gauge …
Test of CP invariance in vector-boson fusion production of the Higgs boson in the H → ττ channel in proton–proton collisions at s=13TeV with the ATLA…
2020
A test of CP invariance in Higgs boson production via vector-boson fusion is performed in the H → ττ decay channel. This test uses the Optimal Observable method and is carried out using 36.1 fb−1 of √s = 13 TeV proton–proton collision data collected by the ATLAS experiment at the LHC. Contributions from CP-violating interactions between the Higgs boson and electroweak gauge bosons are described by an effective field theory, in which the parameter ˜ d governs the strength of CP violation. No sign of CP violation is observed in the distributions of the Optimal Observable, and ˜ d is constrained to the interval [−0.090, 0.035] at the 68% confidence level (CL), compared to an expected interval …
Neutrino electron scattering and electroweak gauge structure: Future tests
1997
Low-energy high-resolution neutrino-electron scattering experiments may play an important role in testing the gauge structure of the electroweak interaction. We propose the use of radioactive neutrino sources (e.g. $^{51}$Cr) in underground experiments such as BOREXINO, HELLAZ and LAMA. As an illustration, we display the sensitivity of these detectors in testing the possible existence of extra neutral gauge bosons, both in the framework of E_6 models and of models with left-right symmetry.
Precision measurements of electroweak gauge boson parameters at LEP
2000
Abstract Over ten years after the start-up of LEP and four years after the completion of the energy scans around the Z resonance the analyses of the Z parameters by the four experiments Aleph, Delphi and L3 are final and the Opal results are very close to final. The analyses of the polarisation of τ leptons and measurements of the production rates and forward-backward asymmetries in the heavy flavour sector are approaching their finalisation. Recent data taking nearly doubled the statistics of W± pair events available at Lep and lead to significantly improved preliminary measurements of the W± pair production cross section, the W mass and branching fractions as well as improved limits on no…
WIMP dark matter as radiative neutrino mass messenger
2013
The minimal seesaw extension of the Standard SU(3)(c)circle times SU(2)(L)circle times U(1)(Y) Model requires two electroweak singlet fermions in order to accommodate the neutrino oscillation parameters at tree level. Here we consider a next to minimal extension where light neutrino masses are generated radiatively by two electroweak fermions: one singlet and one triplet under SU(2)(L). These should be odd under a parity symmetry and their mixing gives rise to a stable weakly interactive massive particle (WIMP) dark matter candidate. For mass in the GeV-TeV range, it reproduces the correct relic density, and provides an observable signal in nuclear recoil direct detection experiments. The f…
A theory for scotogenic dark matter stabilised by residual gauge symmetry
2020
Dark matter stability can result from a residual matter-parity symmetry, following naturally from the spontaneous breaking of the gauge symmetry. Here we explore this idea in the context of the $\mathrm{SU(3)_c \otimes SU(3)_L \otimes U(1)_X \otimes U(1)_{N}}$ electroweak extension of the standard model. The key feature of our new scotogenic dark matter theory is the use of a triplet scalar boson with anti-symmetric Yukawa couplings. This naturally implies that one of the light neutrinos is massless and, as a result, there is a lower bound for the $\rm 0\nu\beta\beta$ decay rate.
The forward-backward asymmetry for charm quarks at the Z pole
1995
From 1.4 million hadronic Z decays collected by the ALEPH detector at LEP, an enriched sample of Z --> c $$($) over bar c events is extracted by requiring the presence of a high momentum D*(+/-). The charm quark forward-backward charge asymmetry at the Z pole is measured to be A(FB)(0,c) = (8.0 +/- 2.4)% corresponding to an effective electroweak mixing angle of sin(2) theta(W)(eff) = 0.2302 +/- 0.0054.
Bounds on the triplet fermions in type-III seesaw and implications for collider searches
2021
Type-III seesaw is a simple extension of the Standard Model~(SM) with the SU$(2)_\text{L}$ triplet fermion with zero hypercharge. It can explain the origin of the tiny neutrino mass and flavor mixing. After the electroweak symmetry breaking the light neutrino mass is generated by the seesaw mechanism which further ensures the mixings between the light neutrino and heavy neutral lepton mass eigenstates. If the triplet fermions are around the electroweak scale having sizable mixings with the SM sector allowed by the correct gauge symmetry, they can be produced at the high energy colliders leaving a variety of characteristic signatures. Based on a simple and concrete realizations of the model …
Light composite Higgs and precision electroweak measurements on the Z resonance: An update
2005
We update our analysis of technicolour theories with techniquarks in higher dimensional representations of the technicolour gauge group in the light of the new electroweak precision data on the Z resonance.
K -> pi pi Electroweak Penguins in the Chiral Limit
2002
We report on dispersive and finite energy sum rule analyses of the electroweak penguin matrix elements in the chiral limit. We accomplish the correct perturbative matching (scale and scheme dependence) at NLO in alpha_s, and we describe two different strategies for numerical evaluation.