Search results for " Standard Model"
showing 10 items of 645 documents
Electric dipole moments from flavor-changing supersymmetric soft terms
2008
The standard model predictions for the hadronic electric dipole moments (EDMs) are well far from the present experimental resolutions, thus, the EDMs represent very clean probes of New Physics (effects. Especially, within a minimal supersymmetric standard model framework with flavor-changing (but not necessarily CP-violating) soft terms, large and potentially visible effects to the EDMs are typically expected. In this paper we point out that, beyond-leading-order effects, so far neglected in the literature, dominate over the leading-order effects in large regions of the parameter space; hence, their inclusion in the evaluation of the hadronic EDMs is unavoidable.
Bounds on models with one latticized extra dimension
2003
We study an extension of the standard model with one latticized extra dimension accessible to all fields. The model is characterized by the size of the extra dimension and the number of sites, and contains a tower of massive particles. At energies lower than the mass of the new particles there are no tree-level effects. Therefore, bounds on the scale of new physics can only be set from one-loop processes. We calculate several observables sensitive to loop-effects, such as the $\rho$ parameter, $b\to s \gamma$, $Z\to b\bar b$, and the $B^0\rightleftharpoons\bar{B}^0$ mixing, and use them to set limits on the lightest new particles for different number of sites. It turns out that the continuo…
The self-couplings of vector bosons: does LEP-1 obviate LEP-2?
1992
Abstract Theories beyond the standard model (“meta-theories”) are severely constrained by the current body of data and must necessarily respect the standard gauge symmetry. We analyze the constraints on two generic types of meta-theory, in which fundamental scalar do or do not exist. The novel low-energy effects can be comprehensively described by grafting onto the standard lagrangian new operators that - in the sense of a Taylor expansion - form a complete set. Completeness calls for consideration of previously discarded operators, and for a thorough exploitation of the equations of motion. We illustrate the current strictures by focusing on the allowed range of departures from the most cr…
Neutrino mass and invisible Higgs decays at the LHC
2015
The discovery of the Higgs boson suggests that also neutrinos get their mass from spontaneous symmetry breaking. In the simplest ungauged lepton number scheme, the Standard Model (SM) Higgs has now two other partners: a massive CP-even, as well as the massless Nambu-Goldstone boson, called majoron. For weak-scale breaking of lepton number the invisible decays of the CP- even Higgs bosons to the majoron lead to potentially copious sources of events with large missing energy. Using LHC results we study how the constraints on invisible decays of the Higgs boson restrict the relevant parameters, substantially extending those previously derived from LEP and shedding light on spontaneous lepton n…
Mixing asymmetries inBmeson systems, the D0 like-sign dimuon asymmetry, and generic new physics
2015
The measurement of a large like-sign dimuon asymmetry $A^b_{SL}$ by the D0 experiment at the Tevatron departs noticeably from Standard Model expectations and it may be interpreted as a hint of physics beyond the Standard Model contributing to $\Delta B\neq 0$ transitions. In this work we analyse how the natural suppression of $A^b_{SL}$ in the SM can be circumvented by New Physics. We consider generic Standard Model extensions where the charged current mixing matrix is enlarged with respect to the usual $3\times 3$ unitary Cabibbo-Kobayashi-Maskawa matrix, and show how, within this framework, a significant enhancement over Standard Model expectations for $A^b_{SL}$ is easily reachable throu…
Light vector mediators facing XENON1T data
2020
Recently the XENON1T collaboration has released new results on searches for new physics in low-energy electronic recoils. The data shows an excess over background in the low-energy tail, particularly pronounced at about $2-3$ keV. With an exposure of $0.65$ tonne-year, large detection efficiency and energy resolution, the detector is sensitive as well to solar neutrino backgrounds, with the most prominent contribution given by $pp$ neutrinos. We investigate whether such signal can be explained in terms of new neutrino interactions with leptons mediated by a light vector particle. We find that the excess is consistent with this interpretation for vector masses below $\lesssim 0.1$ MeV. The r…
A Supersymmetric Solution to the Solar and Atmospheric Neutrino Problems
1999
The simplest unified extension of the Minimal Supersymmetric Standard Model with bi-linear R--Parity violation provides a predictive scheme for neutrino masses which can account for the observed atmospheric and solar neutrino anomalies in terms of bi-maximal neutrino mixing. The maximality of the atmospheric mixing angle arises dynamically, by minimizing the scalar potential, while the solar neutrino problem can be accounted for either by large or by small mixing oscillations. One neutrino picks up mass by mixing with neutralinos, while the degeneracy and masslessness of the other two is lifted only by loop corrections. Despite the smallness of neutrino masses R-parity violation is observab…
Minimalistic Neutrino Mass Model
2000
We consider the simplest model which solves the solar and atmospheric neutrino puzzles, in the sense that it contains the smallest amount of beyond the Standard Model ingredients. The solar neutrino data is accounted for by Planck-mass effects while the atmospheric neutrino anomaly is due to the existence of a single right-handed neutrino at an intermediate mass scale between 10^9 GeV and 10^14 GeV. Even though the neutrino mixing angles are not exactly predicted, they can be naturally large, which agrees well with the current experimental situation. Furthermore, the amount of lepton asymmetry produced in the early universe by the decay of the right-handed neutrino is very predictive and ma…
Measurement of theCP-violation parameter ofB0mixing and decay withpp¯→μμXdata
2006
We measure the dimuon charge asymmetry A in p (p) over bar collisions at a center of mass energy root s=1960 GeV. The data was recorded with the D0 detector and corresponds to an integrated luminosity of approximately 1.0 fb(-1). Assuming that the asymmetry A is due to asymmetric B-0 (B) over bar (0) mixing and decay, we extract the CP-violation parameter of B-0 mixing and decay: ((epsilon B0))/(1+vertical bar epsilon B0 vertical bar 2)=(AB0)/(4)= -0.0023 +/- 0.0011(stat)+/- 0.0008(syst).A(B)(0) is the dimuon charge asymmetry from decays of B-0(B) over bar (0) pairs. The general case, with CP violation in both B-0 and B-s(0) systems, is also considered. Finally we obtain the forward-backwar…
Neutrino masses and mixings from supersymmetry with bilinear R-parity violation: A theory for solar and atmospheric neutrino oscillations
2000
The simplest unified extension of the MSSM with bi-linear R--Parity violation naturally predicts a hierarchical neutrino mass spectrum, in which one neutrino acquires mass by mixing with neutralinos, while the other two get mass radiatively. We have performed a full one-loop calculation of the neutralino-neutrino mass matrix in the bi-linear \rp MSSM, taking special care to achieve a manifestly gauge invariant calculation. Moreover we have performed the renormalization of the heaviest neutrino, needed in order to get meaningful results. The atmospheric mass scale and maximal mixing angle arise from tree-level physics, while solar neutrino scale and oscillations follow from calculable one-lo…