Search results for "Particle physics"
showing 10 items of 6826 documents
Bounds on new Majoron models from the Heidelberg-Moscow experiment
1996
In recent years several new Majoron models were invented to avoid shortcomings of the classical models while leading to observable decay rates in double beta experiments. We give the first experimental half life bounds on double beta decays with new Majoron emission and derive bounds on the effective neutrino--Majoron couplings from the data of the $^{76}Ge$ HEIDELBERG--MOSCOW experiment. While stringent half life limits for all decay modes and the coupling constants of the classical models were obtained, small matrix elements and phase space integrals \cite{hir95,pae95} result in much weaker limits on the effective coupling constants of the new Majoron models.
Constraining new interactions with leptonic tau decays
1995
13 páginas, 10 tablas.-- PACS number(s): 13.35.Dx, 12.60.Cn, 12.60.Fr
Massless Spectra and Gauge Couplings at One-Loop on Non-Factorisable Toroidal Orientifolds
2018
So-called `non-factorisable' toroidal orbifolds can be rewritten in a factorised form as a product of three two-tori by imposing an additional shift symmetry. This finding of Blaszczyk et al., arXiv:1111.5852, provides a new avenue to Conformal Field Theory methods, by which the vector-like massless matter spectrum - and thereby the type of gauge group enhancement on orientifold invariant fractional D6-branes - and the one-loop corrections to the gauge couplings in Type IIA orientifold theories can be computed in addition to the well-established chiral matter spectrum derived from topological intersection numbers among three-cycles. We demonstrate this framework for the $\mathbb{Z}_4 \times…
Search for supersymmetric particles with R-parity violation in Z decays
1995
Searches for supersymmetric particles produced in e(+)e(-) interactions at the Z peak have been performed under the assumptions that R-parity is not conserved, that the dominant R-parity violating coupling involves only leptonic fields, and that the lifetime of the lightest supersymmetric particle can be neglected. In a data sample collected by the ALEPH detector at LEP up to 1993, and corresponding to almost two million hadronic Z decays, no signal was observed. As a result, supersymmetric particle masses and couplings are at least as well constrained as under the usual assumption of R-parity conservation.
Bounding effective operators at the one-loop level: the case of four-fermion neutrino interactions
1994
The contributions of non-standard four-neutrino contact interactions to electroweak observables are considered at the one-loop level by using the effective quantum field theory. The analysis is done in terms of three unknown parameters: the strength of the non-standard neutrino interactions, $\tilde{F}$, an additional derivative coupling needed to renormalize the divergent contributions that appear when the four-neutrino interactions are used at the loop level and a non-standard non-derivative $Z$-${\bar\nu} \nu$ coupling. Then, the precise measurements of the invisible width of the $Z$-boson at LEP and the data on the neutrino deep-inelastic scattering yield the result $\tilde{F} = (-100 \…
Yukawa Alignment in the Two-Higgs-Doublet Model
2009
5 páginas, 1 tabla.-- PACS numbers: 12.60.Fr, 11.30.Hv, 12.15.Mm, 14.80.Cp
Higgs boson self-coupling measurements using ratios of cross sections
2013
We consider the ratio of cross sections of double-to-single Higgs boson production at the Large Hadron Collider at 14 TeV. Since both processes possess similar higher-order corrections, leading to a cancellation of uncertainties in the ratio, this observable is well-suited to constrain the trilinear Higgs boson self-coupling. We consider the scale variation, parton density function uncertainties and conservative estimates of experimental uncertainties, applied to the viable decay channels, to construct expected exclusion regions. We show that the trilinear self-coupling can be constrained to be positive with a 600/fb LHC dataset at 95% confidence level. Moreover, we demonstrate that we expe…
Measuring anomalous couplings inH→WW*decays at the International Linear Collider
2013
The measurement of the Higgs coupling to $W$ bosons is an important test of our understanding of the electroweak symmetry-breaking mechanism. We study the sensitivity of the International Linear Collider (ILC) to the presence of anomalous $H{W}^{+}{W}^{\ensuremath{-}}$ couplings using $ZH\ensuremath{\rightarrow}\ensuremath{\nu}\overline{\ensuremath{\nu}}W{W}^{*}\ensuremath{\rightarrow}\ensuremath{\nu}\overline{\ensuremath{\nu}}4j$ events. Using an effective Lagrangian approach, we calculate the differential decay rates of the Higgs boson including the effects of new dimension-five operators. We present a Monte Carlo simulation of events at the ILC, using a full detector simulation based on …
Limits on anomalous trilinear gauge couplings fromWW→e+e−,WW→e±μ∓, andWW→μ+μ−events frompp¯collisions ats=1.96 TeV
2006
Limits are set on anomalous WW gamma and WWZ trilinear gauge couplings using W+W--> e(+)nu(e)e(-)(nu) over bar (e), W+W--> e(+/-)nu(e)mu(-/+)nu(mu), and W+W-->mu(+)nu(mu)mu(-)(nu) over bar (mu) events. The data set was collected by the Run II D0 detector at the Fermilab Tevatron Collider and corresponds to approximately 250 pb(-1) of integrated luminosity at root s=1.96 TeV. Under the assumption that the WW gamma couplings are equal to the WWZ couplings and using a form factor scale of Lambda=2.0 TeV, the combined 95% C.L. one-dimensional coupling limits from all three channels are -0.32 <Delta kappa < 0.45 and -0.29 <lambda < 0.30.
Footprints of a left-right symmetric model in a muon collider
2000
Abstract The double charged Higgs bosons, Δ ±± , are one of the benchmarks of left-right symmetric models. We discuss their production and demonstrate that even for small values of the Δ ++ l − l − coupling, they would produce observable signals at muon colliders.