Search results for "weak interaction"
showing 10 items of 431 documents
High-precision determination of the $K_{e3}$ radiative corrections
2021
We report a high-precision calculation of the Standard Model electroweak radiative corrections in the $K\to \pi e^+\nu(\gamma)$ decay as a part of the combined theory effort to understand the existing anomaly in the determinations of $V_{us}$. Our new analysis features a chiral resummation of the large infrared-singular terms in the radiative corrections and a well-under-control strong interaction uncertainty based on the most recent lattice QCD inputs. While being consistent with the current state-of-the-art results obtained from chiral perturbation theory, we reduce the existing theory uncertainty from $10^{-3}$ to $10^{-4}$. Our result suggests that the Standard Model electroweak effects…
The Hunt for New Physics at the Large Hadron Collider
2010
233 páginas.-- AHEP Group: et al..-- El Pdf del artículo es la versión pre-print: arXiv.1001.2693v1.-- Trabajo presentado al "The International Workshop on Beyond the Standard Model Physics and LHC Signatures (BSM-LHC) celebrado en Boston (USA) del 2 al 4 de junio de 2009.
Relaxing cosmological neutrino mass bounds with unstable neutrinos
2020
At present, cosmological observations set the most stringent bound on the neutrino mass scale. Within the standard cosmological model ($\Lambda$CDM), the Planck collaboration reports $\sum m_\nu < 0.12\,\text{eV}$ at 95% CL. This bound, taken at face value, excludes many neutrino mass models. However, unstable neutrinos, with lifetimes shorter than the age of the universe $\tau_\nu \lesssim t_U$, represent a particle physics avenue to relax this constraint. Motivated by this fact, we present a taxonomy of neutrino decay modes, categorizing them in terms of particle content and final decay products. Taking into account the relevant phenomenological bounds, our analysis shows that 2-body deca…
Higgs-Inflaton Mixing and Vacuum Stability
2019
The quartic and trilinear Higgs field couplings to an additional real scalar are renormalizable, gauge and Lorentz invariant. Thus, on general grounds, one expects such couplings between the Higgs and an inflaton in quantum field theory. In particular, the (often omitted) trilinear coupling is motivated by the need for reheating the Universe after inflation, whereby the inflaton decays into the Standard Model (SM) particles. Such a coupling necessarily leads to the Higgs-inflaton mixing, which could stabilize the electroweak vacuum by increasing the Higgs self-coupling. We find that the inflationary constraints on the trilinear coupling are weak such that the Higgs-inflaton mixing up to ord…
Measurements of the Lineshape of the $Z^{0}$ and Determination of Electroweak Parameters from its Hadronic and Leptonic Decays
1994
Abstract: During the LEP running periods in 1990 and 1991 DELPHI has accumulated approximately 450000 Z0 decays into hadrons and charged leptons. The increased event statistics coupled with improved analysis techniques and improved knowledge of the LEP beam energies permit significantly better measurements of the mass and width of the Z0 resonance. Model independent fits to the cross sections and leptonic forward-backward asymmetries yield the following Z0 parameters: the mass and total width M(Z) = 91.187 +/- 0.009 GeV, GAMMA(Z) = 2.486 +/- 0.012 GeV, the hadronic and leptonic partial widths GAMMA(had) = 1.725 +/- 0.012GeV, GAMMA(l) = 83.01 +/- 0.52 MeV, the invisible width GAMMA(inv) = 51…
Fully Differential Higgs Pair Production in Association With a $W$ Boson at Next-to-Next-to-Leading Order in QCD
2017
To clarify the electroweak symmetry breaking mechanism, we need to probe the Higgs self-couplings, which can be measured in Higgs pair productions. The associated production with a vector boson is special due to a clear tag in the final state. We perform a fully differential next-to-next-to-leading-order calculation of the Higgs pair production in association with a $W$ boson at hadron colliders, and present numerical results at the 14 TeV LHC and a future 100 TeV hadron collider.
Fingerprints of heavy scales in electroweak effective Lagrangians
2017
The couplings of the electroweak effective theory contain information on the heavy-mass scales which are no-longer present in the low-energy Lagrangian. We build a general effective Lagrangian, implementing the electroweak chiral symmetry breaking $SU(2)_L\otimes SU(2)_R\to SU(2)_{L+R}$, which couples the known particle fields to heavier states with bosonic quantum numbers $J^P=0^\pm$ and $1^\pm$. We consider colour-singlet heavy fields that are in singlet or triplet representations of the electroweak group. Integrating out these heavy scales, we analyze the pattern of low-energy couplings among the light fields which are generated by the massive states. We adopt a generic non-linear realiz…
Heavy Higgs of the Twin Higgs models
2018
Twin Higgs models are the prime illustration of neutral naturalness, where the new particles of the twin sector, gauge singlets of the Standard Model (SM), ameliorate the little hierarchy problem. In this work, we analyse phenomenological implications of the heavy Higgs of the Mirror Twin Higgs and Fraternal Twin Higgs models, when electroweak symmetry breaking is linearly realized. The most general structure of twin Higgs symmetry breaking, including explicit soft and hard breaking terms in the scalar potential, is employed. The direct and indirect searches at the LHC are used to probe the parameter space of Twin Higgs models through mixing of the heavy Higgs with the SM Higgs and decays o…
Flavour alignment in multi-Higgs-doublet models
2017
Extended electroweak scalar sectors containing several doublet multiplets require flavour-aligned Yukawa matrices to prevent the appearance at tree level of unwanted flavour- changing neutral-current transitions. We analyse the misalignment induced by one-loop quantum corrections and explore possible generalizations of the alignment condition and their compatibility with current experimental constraints. The hypothesis of flavour alignment at a high scale turns out to be consistent with all known phenomenological tests.
A 125 GeV composite Higgs boson versus flavour and electroweak precision tests
2013
A composite Higgs boson of 125 GeV mass, only mildly fine-tuned, requires top partners with a semi-perturbative coupling and a mass not greater than about a TeV. We analyze the strong constraints on such picture arising from flavour and electroweak precision tests in models of partial compositeness. We consider different representations for the composite fermions and compare the case of an anarchic flavour structure to models with a U(3)^3 and U(2)^3 flavour symmetry. Although non trivially, some models emerge that look capable of accommodating a 125 GeV Higgs boson with top partners in an interesting mass range for discovery at the LHC as well as associated flavour signals.