Fermionic Decay Research Articles

Squark decays in MSSM under the cosmological bounds

We present the numerical investigation of the fermionic two-body decays of squarks in the minimal supersymmetric standard model with complex parameters. In the analysis, we particularly take into account the cosmological bounds imposed by Wilkinson Microwave Anisotropy Probe data. We find that the phase dependences of the decay widths of the third family squarks, as well as those of the first and second families, are quite significant which can provide viable probes of additional CP sources. We plot the CP-phase dependences for each fermionic two-body decay channel of squarks (i = 1, 2, q = u, d, c, s, t, b) and speculate about the branching ratios and total (two-body) decay widths.

Dominant decays of scalar leptoquarks and scalar gluons in the minimal four-color symmetry model

Fermionic and weak decays of the scalar leptoquarks S = S 1 (+) , S 1 (−) , and S m and the scalar gluons F = F 1 and F 2 predicted by the minimal model involving four-color symmetry and the Higgs mechanism of quark-and lepton-mass splitting are considered. The widths and the branching ratios are calculated for these decays, and the results are analyzed versus the couplings and masses of decaying particles. It is shown that, at relatively small mass splittings Δm within scalar doublets (Δm < m W), the fermionic decays S 1 (+) → tl j + , S 1 (−) → v i $$\tilde b$$ , S m → t $$\tilde \nu $$ j, F 1 → t $$\tilde b$$ , and F 2 → t $$\tilde t$$ , which are characterized by few-GeV widths for m S, m F m W, the weak decays S → S′W and F → F’W compete with the above fermionic decays. In the case of m S < m t, the processes S 1 (+) → cl j + , S 1 (−) → v i $$\tilde b$$ , S m → bl j + , and S m → c $$\tilde \nu $$ j, whose total branching ratios are Br(S 1 (+) → cl +) ≈ Br(S 1 (−) → v $$\tilde b$$ ) ≈ 1, Br(S m → bl +) ≈ 0.9, and Br(S m → c $$\tilde \nu $$ ) ≈ 0.1, appear to be dominant decays of scalar leptoquarks. Searches for these decays at LHC and the Tevatron are of interest.

Top and bottom squarks decays under cosmological bounds

Abstract We investigate the fermionic decays of top squarks t ˜ 1 , 2 and bottom squarks b ˜ 1 , 2 in the Minimal Supersymmetric Standard Model with complex parameters M 1 , μ , A t and A b . In the analysis we particularly take into account the cosmological bounds imposed by WMAP data. We plot the CP phase dependences of stop and sbottom decay widths.

Reconsidering extra time-like dimensions

In this study we reconsider the phenomenological problems related to tachyonic modes in the context of extra time-like dimensions. First we reconsider a lower bound on the size of extra time-like dimensions and improve on the conclusion in the literature. Next we discuss the issues of spontaneous decay of stable fermions through tachyonic decays and disappearance of fermions due to tachyonic contributions to their self-energies. We find that the tachyonic modes due to extra time-like dimensions are less problematic than the tachyonic modes in the usual 4-dimensional setting because the most troublesome Feynman diagrams are forbidden once the conservation of momentum in the extra time-like dimensions is imposed.

FERMIONIC DECAYS OF SCALAR LEPTOQUARKS AND SCALAR GLUONS IN THE MINIMAL FOUR-COLOR SYMMETRY MODEL

Fermionic decays of the scalar leptoquarks [Formula: see text], [Formula: see text], Sm and of the scalar gluons F=F1, F2 predicted by the four-color symmetry model with the Higgs mechanism of the quark–lepton mass splitting are investigated. Widths and branching ratios of these decays are calculated and analyzed in dependence on coupling constants and on masses of the decaying particles. It is shown that the decays [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] are dominant with the widths of order of a few GeV for mS, mF&lt; 1 TeV and with the total branching ratios close to 1. In the case of mS&lt;mt the dominant scalar leptoquark decays are [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] with the total branching ratios [Formula: see text], [Formula: see text] and [Formula: see text]. A search for such decays at the LHC and Tevatron may be of interest.

Atom-Molecule Coherence in a One-Dimensional System

We study a model of one-dimensional fermionic atoms with a narrow Feshbach resonance that allows them to bind in pairs to form bosonic molecules. We show that at low energy, a coherence develops between the molecule and fermion Luttinger liquids. At the same time, a gap opens in the spin excitation spectrum. The coherence implies that the order parameters for the molecular Bose-Einstein condensation and the atomic BCS pairing become identical. Moreover, both bosonic and fermionic charge density wave correlations decay exponentially, in contrast with a usual Luttinger liquid. We exhibit a Luther-Emery point where the systems can be described in terms of noninteracting pseudofermions. At this point we discuss the threshold behavior of density-density response functions.

Scalar condensate decay in a fermionic heat bath in the early universe

We consider one-loop thermal effects on the decay of a scalar field zero mode initiallydominating the energy density of the universe. We assume fermionic decay channels andtake into account the effects due to both particle and hole excitations, and presentapproximate expressions for the absorption and decay rates. We apply the results to theinflaton and solve the Boltzmann equations to find the temperature evolution of thefermionic plasma. We show that the reheat temperature can be greater thanthe inflaton mass if the inflaton decays into more than one fermionic species.

T-odd correlations in the decay of scalar fermions

We define a CP sensitive asymmetry in the sfermion decays $\ti f \to f \ti\chi^0_j \ell \bar \ell, f \ti\chi^0_j q \bar q$, based on triple product correlations between the momenta of the outgoing fermions. We study this asymmetry in the MSSM with complex parameters. We show that the asymmetry is sensitive to the phases of the parameters $\mu$ and $M_1$. The leading contribution stems from the decay chain $\ti f\to f \ti\chi^0_j\to f \ti\chi^0_1 Z\to f \ti\chi^0_1 \ell \bar \ell (f \ti\chi^0_1 q \bar q)$, for which we obtain analytic formulae for the amplitude squared. The asymmetry can go up to 3% for $\ti f\to f \ti\chi^0_1 \ell \bar \ell$, and up to 20% for $\ti f\to f \ti\chi^0_1 q \bar q$. We also estimate the rates necessary to measure the asymmetry.

Improved full one-loop corrections toA0→f1f̃¯2andf2→f1A0

We calculate the full electroweak one-loop corrections to the decay of the CP-odd Higgs boson ${A}^{0}$ into scalar fermions in the minimal supersymmetric extension of the standard model (MSSM). For this purpose many parameters of the MSSM have to be properly renormalized in the on-shell renormalization scheme. We have also included the supersymmetric QCD corrections. For the decay into bottom squarks and tau sleptons, especially for large $\mathrm{tan}\ensuremath{\beta},$ the corrections can be very large, making the perturbation expansion unreliable. We solve this problem by an appropriate definition of the tree-level coupling in terms of running fermion masses and running trilinear couplings ${A}_{f}.$ We also discuss the decay of heavy scalar fermions into light scalar fermions and ${A}^{0}.$ We find that the corrections can be sizable and therefore cannot be neglected.

Fermionic decays of sfermions in the MSSM: a full one-loop calculation

We present a full one-loop calculation of the electroweak corrections to the partial decay widths of the fermionic modes of sfermions Γ( f ̃ → f′ x) . The main technical points of the renormalization are presented, and the main features of the results are discussed.

QED radiative corrections under the SANC project

Abstract Automatic calculations of the QED radiative corrections in the framework of the SANC computer system is described. A collection of the computer programs written in FORM3 language is aimed at compiling a database of analytic results to be used to theoretically support the experiments on high-energy accelerators. Presented here is the scheme of automatic analytical calculations of the QED radiative corrections to the fermionic decays of the Z, H and W boson in the framework of the SANC system.

Single-spin asymmetry in pion production in polarized proton–proton collisions and odderon

Single-spin asymmetry appears due to the interference of single and double gluon exchanges between protons. A heavy fermion model is used to describe the jet production in the interaction of the gluon with the proton implying further averaging over its mass. As usual in one-spin correlations, the imaginary part of the double gluon exchange amplitude plays the relevant role. The asymmetry in the inclusive set-up with the pion tagged in the fragmentation region of the polarized proton does not depend on the centre of mass energy in the limits of its large values. The lowest order radiative corrections to the polarized and unpolarized contributions to the differential cross sections are calculated in the leading logarithmic approximation. In general, a coefficient of logarithm of the ratio of cms energy to the pion mass depends on the transversal momentum of the pion. This ratio of the lowest order contribution to the asymmetry may be interpreted as the partial contribution to the odderon intercept. The ratio of the relevant contributions in the unpolarized case can be associated with the partial contribution to the pomeron intercept. The numerical results given for the model describe the jet as heavy fermion decay fragments.

τsleptons andτsneutrino in the minimal supersymmetric standard model with complex parameters

We present a phenomenological study of $\ensuremath{\tau}$ sleptons ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\tau}}}_{1,2}$ and $\ensuremath{\tau}$ sneutrinos ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ in the minimal supersymmetric standard model with complex parameters ${A}_{\ensuremath{\tau}},$ $\ensuremath{\mu}$ and ${M}_{1}.$ We analyze the production and decays of the ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\tau}}}_{1,2}$ and ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ at a future ${e}^{+}{e}^{\ensuremath{-}}$ collider. We present numerical predictions for the important decay rates, paying particular attention to their dependence on the complex parameters. The branching ratios of the fermionic decays of ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\tau}}}_{1}$ and ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ show a significant phase dependence for $\mathrm{tan}\ensuremath{\beta}\ensuremath{\lesssim}10.$ For $\mathrm{tan}\ensuremath{\beta}\ensuremath{\gtrsim}10$ the branching ratios for the ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\tau}}}_{2}$ decays into Higgs bosons depend very sensitively on the phases. We show how information on the phase ${\ensuremath{\varphi}}_{{A}_{\ensuremath{\tau}}}$ and the other fundamental ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\tau}}}_{i}$ parameters can be obtained from measurements of the ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\tau}}}_{i}$ masses, polarized cross sections and bosonic and fermionic decay branching ratios, for small and large $\mathrm{tan}\ensuremath{\beta}$ values. We estimate the expected errors of these parameters. Given favorable conditions, the error of ${A}_{\ensuremath{\tau}}$ is about 10% to 20%, while the errors of the remaining stau parameters are in the range of approximately 1% to 3%. We also show that the induced electric dipole moment of the $\ensuremath{\tau}$ lepton is well below the current experimental limit.

Fermionic decays of sfermions: a complete discussion at one-loop order

We present a definition of an on-shell renormalization scheme for the sfermion and chargino-neutralino sector of the Minimal Supersymmetric Standard Model (MSSM). Then, apply this renormalization framework to the interaction between charginos/neutralinos and sfermions. A kind of universal corrections is identified, which allow to define effective chargino/neutralino coupling matrices. In turn, these interactions generate (universal) non-decoupling terms that grow as the logarithm of the heavy mass. Therefore the full MSSM spectrum must be taken into account in the computation of radiative corrections to observables involving these interactions. As an application we analyze the full one-loop electroweak radiative corrections to the partial decay widths \Gamma(\tilde{f} -> f\neut) and \Gamma(\tilde{f} -> f'\cplus) for all sfermion flavours and generations. These are combined with the QCD corrections to compute the corrected branching ratios of sfermions. It turns out that the electroweak corrections can have an important impact on the partial decay widths, as well as the branching ratios, in wide regions of the parameter space. The precise value of the corrections is strongly dependent on the correlation between the different particle masses.

Influence of CP and CPT on production and decay of Dirac and Majorana fermions

The consequences of CP and CPT invariance for production and subsequent decay of Dirac and Majorana fermions in polarized fermion--antifermion annihilation are analytically studied. We derive general symmetry relations for the production spin density matrix and for the three--particle decay matrices and obtain constraints for the polarization and the spin--spin correlations of Dirac and Majorana fermions. We prove that only for Majorana fermions the energy and opening angle distribution factorizes exactly into contributions from production and decay if CP is conserved.

A search for excited fermions at HERA

A search for excited fermions f $^*$ of the first generation in $e^+p$ scattering at the collider HERA is presented using H1 data with an integrated luminosity of 37 pb $^{-1}$ . All electroweak decays of excited fermions, f $^* \rightarrow$ f $\gamma,$ f W,f Z are considered and all possible final states resulting from the Z orW hadronic decays or decays into leptons of the first two generations are taken into account. No evidence for f $^*$ production is found. Mass dependent exclusion limits on cross-sections and on the ratio of coupling constants to the compositeness scale are derived.

Finite temperature effects onCP-violating asymmetries

We compute the CP violating decay asymmetries relevant for baryogenesis scenarios involving the out of equilibrium decays of heavy particles, including the finite temperature effects arising from the background of light thermal particles which are present during the decay epoch. Thermal effects can modify the size of CP violation by a sizeable fraction in the decay of scalar particles, but we find interesting cancellations in the thermal corrections affecting the asymmetries in the decays of fermions, as well as in the decay of scalars in supersymmetric theories. We also estimate the effects which arise from the motion of the decaying particles with respect to the background plasma.

Search for evidence of compositeness at LEP I

Extensive searches for evidence of compositeness of quarks and leptons have been made in the complete set of ALEPH data from LEP running at the Z peak. These include searches for radiative and weak decays of excited fermions, produced either in pairs or singly, and a scalar partner of the Z. Coupling and branching ratio limits deduced from these searches are presented.

Two loop O(Nf alpha 2s) corrections to the decay width of the Higgs boson to two massive fermions.

We present an analytical calculation of additional real or virtual radiation of a light fermion pair in the fermionic decay of the Higgs boson H\ensuremath{\rightarrow}${\mathit{f}}_{1}$f${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{1}$ for arbitrary ratios of the Higgs boson mass to the ${\mathit{f}}_{1}$ fermion mass. This result gives us a value of the O(${\mathit{N}}_{\mathit{f}}$${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}^{2}$) radiative correction to the inclusive decay rate H\ensuremath{\rightarrow}${\mathit{f}}_{1}$f${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{1}$. Using this result in the framework of the Brodsky-Mackenzie-Lepage scheme, we discuss the question of the scale setting in the one-loop QCD correction to the decay width H\ensuremath{\rightarrow}${\mathit{f}}_{1}$f${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{1}$ for an arbitrary relation between the Higgs boson and fermion masses. \textcopyright{} 1996 The American Physical Society.

Erratum: QCD corrections to Higgs boson self-energies and fermionic decay widths

Erratum: QCD corrections to Higgs boson self-energies and fermionic decay widths