Search results for "Fermi"
showing 10 items of 1388 documents
QED one-loop corrections to radiative muon decay
1994
Based upon the Fermi interaction, the differential decay rate of the radiative muon decay including one-loop radiative corrections is determined to the order ${G}_{F}^{2}{\ensuremath{\alpha}}^{2}$. Essential aspects of the calculation are exhibited. After cancellation of IR divergences, the double radiative muon decay is included. Some initial applications are considered.
Self-interacting dark matter and cosmology of a light scalar mediator
2016
We consider a fermionic dark matter candidate interacting via a scalar mediator coupled with the Standard Model through a Higgs portal. We consider a general setting including both scalar and pseudoscalar interactions between the scalar and fermion, and illustrate the relevant features for dark matter abundance, direct search limits and collider constraints. The case where dark matter has a self-interaction strength $⟨{\ensuremath{\sigma}}_{V}⟩/{m}_{\ensuremath{\psi}}\ensuremath{\sim}0.1--1\text{ }\text{ }{\mathrm{cm}}^{2}/\mathrm{g}$ is strongly constrained, in particular by the big bang nucleosynthesis. We show that these constraints can be alleviated by introducing a new light sterile ne…
Search for the Scalar Top Quark inpp¯Collisions ats=1.8TeV
2002
We have performed a search for scalar top quark (stop) pair production in the inclusive electron-muon-missing transverse energy final state, using a sample of p (p) over bar events corresponding to 108.3 pb (-1) of data collected with the D0 detector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the sneutrino is the lightest supersymmetric particle. For the dominant decays of the lightest stop, (t) over tilde-->b (χ) over tilde (+)(1) and (t) over tilde-->bl (ν) over tilde , no evidence for signal is found. We derive cross-section limits as a function of stop ((t) over tilde), chargino ((χ) over tilde (+)(1)), and sneutrino ((ν) …
Observation of Single Top Quark Production
2009
We report observation of the electroweak production of single top quarks in ppbar collisions at sqrt(s) = 1.96 TeV based on 2.3 fb^-1 of data collected by the D0 detector at the Fermilab Tevatron Collider. Using events containing an isolated electron or muon and missing transverse energy, together with jets originating from the fragmentation of b quarks, we measure a cross section of sigma(ppbar -> tb + X, tqb + X) = 3.94 +- 0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5 x 10^-7, corresponding to a 5.0 standard deviation significance for the observation.
Dark Matter in Leptoquark Portal
2021
A beyond the standard model portal scenario for Majorana fermion dark matter (DM) particle with leptoquark being the mediator field is of the main focus of this study. We explore the parameter space of the only unknown coupling in the model which is sensitive to all three main features of a DM model, namely, relic density, direct detection as well as indirect detection, while being consistent with the collider searches. The AMS-02 data for antiproton flux imposes stringent bound till date which excludes the DM mass up to \(400\,\)GeV at 95% C.L. The LUX 2016 data for DM-neutron scattering cross section allows the region compatible with relic density; however, the future sensitivity of LZ ex…
The Topological Phase Transitions Related to Fermion Condensate
2014
In this chapter, we consider so-called topological phase transitions, taking place in normal Fermi liquid. In other words, here we are dealing with different instabilities of normal Fermi liquids relative to several kinds of perturbations of initial quasiparticle spectrum \(\varepsilon (p)\) and occupation numbers \(n(p)\) associated with the emergence of a multi-connected Fermi surface. Depending on the parameters and analytical properties of the Landau interaction, such instabilities lead to several possible types of restructuring of initial Landau Fermi liquid ground state. This restructuring generates topologically distinct phases. One of them is the FC discussed above, another one belo…
Renormalization of the Fröhlich constant for electrons in a quantum dot
2002
Recent experimental investigations of far-infrared attenuation in GaAs/InAs quantum dot in magnetic field and measurements of photoluminescence features for smaller pyramid-shape GaAs/InAs quantum dots indicated an enhancement of coupling of longitudinal optical phonons with confined electrons, which manifested itself in a significant increase of the effective Frohlich constant in comparison to its bulk value. We give a simple quasiclassical explanation of this enhancement and relate the renormalization of the Frohlich constant with the dot diameter.
Some physical appearances of vector coherent states and coherent states related to degenerate Hamiltonians
2005
In the spirit of some earlier work on the construction of vector coherent states over matrix domains, we compute here such states associated to some physical Hamiltonians. In particular, we construct vector coherent states of the Gazeau-Klauder type. As a related problem, we also suggest a way to handle degeneracies in the Hamiltonian for building coherent states. Specific physical Hamiltonians studied include a single photon mode interacting with a pair of fermions, a Hamiltonian involving a single boson and a single fermion, a charged particle in a three dimensional harmonic force field and the case of a two-dimensional electron placed in a constant magnetic field, orthogonal to the plane…
The SVZ plasmon
1985
The sum rule technique of Shifman, Vainshtein and Zakharov is applied to a non-relativistic many-body system, the homogeneous, degenerate electron gas. The operator product expansion for the nonrelativistic correlation function is derived and shown to be equivalent in lowest order to a moment expansion. The nonperturbative terms in this expansion characterize the interacting ground state (“vacuum”) of the system. For the electron gas they can be related to the correlation energy which is very well known. Following as close as possible the SVZ procedure the mass of the plasmon (i.e. the dispersion coefficient of the collective plasma excitation) is calculated and compared with results from c…
Non-Perturbative Renormalization of Lattice Four-Fermion Operators without Power Subtractions
1999
A general non-perturbative analysis of the renormalization properties of $\Delta I=3/2$ four-fermion operators in the framework of lattice regularization with Wilson fermions is presented. We discuss the non-perturbative determination of the operator renormalization constants in the lattice Regularization Independent (RI or MOM) scheme. We also discuss the determination of the finite lattice subtraction coefficients from Ward Identities. We prove that, at large external virtualities, the determination of the lattice mixing coefficients, obtained using the RI renormalization scheme, is equivalent to that based on Ward Identities, in the continuum and chiral limits. As a feasibility study of …