Search results for "Fermion"
showing 10 items of 523 documents
Fibre Bundle for Spin and Charge in General Relativity
2000
The Lorentzian and spin structures of general relativity are shown to allow a natural extension, by means of which the set of possible electromagnetic bundles is linked to the topology and geometry of the underlying causal structure. Further, both the Dirac operator and the electromagnetic potential are obtainable from a single linear connection 1-form.
From classical to operatorial models
2023
Mathematical models for the collective dynamics of interacting and spatially distributed populations find applications in several contexts (biology, ecology, social sciences). Their formulation depends primarily on the (continuous or discrete) description of the space. Reaction-diffusion equations have been widely used in bioecology (morphogenesis, migration of biological species, tumor growth, neuro-degenerative diseases) and in the social sciences (diffusion of opinions or decisionmaking processes), and exhibit complex behaviors (propagation of oscillatory phenomena, pattern formation caused by instability). A reaction–diffusion system exhibits diffusion-driven instability, sometimes call…
A search for light dark matter in XENON10 data
2011
We report results of a search for light (3.5x10^{-42} cm^2, for a dark matter particle mass m_{\chi}=8 GeV. We find that our data strongly constrain recent elastic dark matter interpretations of excess low-energy events observed by CoGeNT and CRESST-II, as well as the DAMA annual modulation signal.
Shining primordial black holes
2021
We study the well-motivated mixed dark matter (DM) scenario composed of a dominant thermal WIMP, highlighting the case of $SU(2)_L$ triplet fermion "winos", with a small fraction of primordial black holes (PBHs). After the wino kinetic decoupling, the DM particles are captured by PBHs leading to the presence of PBHs with dark minihalos in the Milky Way today. The strongest constraints for the wino DM come from the production of narrow line gamma rays from wino annihilation in the Galactic Center. We analyse in detail the viability of the mixed wino DM scenario, and determine the constraints on the fraction of DM in PBHs assuming a cored halo profile in the Milky Way. We show that already wi…
Spin-1 Heisenberg chain and the one-dimensional fermion gas.
1989
The composite-spin representation of the spin-1 Heisenberg chain is used to transform it through the Jordan-Wigner transformation to the one-dimensional fermion gas. To properly include the xy couplings between spins, we also consider the bosonized version of the fermion model. Phase diagrams deduced from the two versions of the fermion model are compared against numerical results for finite Heisenberg chains. One of the symmetries of the spin model is lost in the fermionization, and this leads to a topologically incorrect phase diagram in at least one part of the parameter space. There are clear indications of significant coupling of spin and charge degrees of freedom in the fermion model …
Dark matter from unification
2013
We consider a minimal extension of the Standard Model (SM), which leads to unification of the SM coupling constants, breaks electroweak symmetry dynamically by a new strongly coupled sector and leads to novel dark matter candidates. In this model, the coupling constant unification requires the existence of electroweak triplet and doublet fermions singlet under QCD and new strong dynamics underlying the Higgs sector. Among these new matter fields and a new right handed neutrino, we consider the mass and mixing patterns of the neutral states. We argue for a symmetry stabilizing the lightest mass eigenstates of this sector and determine the resulting relic density. The results are constrained …
Gamma(Z --> bb): A signature of hard mass terms for a heavy top
1988
Abstract We calculate analytically the weak radiative corrections to the weak neutral current gauge boson-bottom fermion vertex, keeping the mass mt of the internal fermion line for the relevant diagrams. We find, to order α, a hard mass-term dependence m t 2 M W 2 of the amplitude, for large mt values. Its origin comes from the unphysical charged Higgs coupling to fermions in the renormalizable gauge or, equivalently, from the longitudinal charged gauge boson couplings. The diagonal Z0 decay width to b-quarks decreases, due to these weak radiative corrections, by 0.6%–2.5% when the top mass mt varies from 45 to 200 GeV.
Analytic results for virtual QCD corrections to Higgs production and decay
2006
We consider the production of a Higgs boson via gluon-fusion and its decay into two photons. We compute the NLO virtual QCD corrections to these processes in a general framework in which the coupling of the Higgs boson to the external particles is mediated by a colored fermion and a colored scalar. We present compact analytic results for these two-loop corrections that are expressed in terms of Harmonic Polylogarithms. The expansion of these corrections in the low and high Higgs mass regimes, as well as the expression of the new Master Integrals which appear in the reduction of the two-loop amplitudes, are also provided. For the fermionic contribution, we provide an independent check of the…
Orthogonality Catastrophe and Decoherence in a Trapped-Fermion Environment
2012
The Fermi edge singularity and the Anderson orthogonality catastrophe describe the universal physics which occurs when a Fermi sea is locally quenched by the sudden switching of a scattering potential, leading to a brutal disturbance of its ground state. We demonstrate that the effect can be seen in the controllable domain of ultracold trapped gases by providing an analytic description of the out-of-equilibrium response to an atomic impurity, both at zero and at finite temperature. Furthermore, we link the transient behavior of the gas to the decoherence of the impurity, and, in particular to the amount of non-markovianity of its dynamics.
B-parameters for ΔS=2 supersymmetric operators
1998
We present a calculation of the matrix elements of the most general set of DeltaS=2 dimension-six four-fermion operators. The values of the matrix elements are given in terms of the corresponding B-parameters. Our results can be used in many phenomenological applications, since the operators considered here give important contributions to K^0--K^0bar mixing in several extensions of the Standard Model (supersymmetry, left-right symmetric models, multi-Higgs models etc.). The determination of the matrix elements improves the accuracy of the phenomenological analyses intended to put bounds on basic parameters of the different models, as for example the pattern of the sfermion mass matrices. Th…