One-loop formulas for H → Zνlνl for l = e, μ, τ in 't Hooft-Veltman gauge

In this paper, we present analytical results for one-loop contributions to the decay processes \begin{document}$ H\rightarrow Z \nu_l\bar{\nu}_l $\end{document} (for \begin{document}$ l = e, \mu, \tau $\end{document}). The calculations are performed within the Standard Model framework in the 't Hooft-Veltman gauge. One-loop form factors are then written in terms of scalar one-loop functions in the standard notations of \begin{document}$ {\tt LoopTools}$\end{document}. As a result, one-loop decay rates for the decay channels can be evaluated numerically by using the package. Furthermore, we analyze the signals of \begin{document}$ H\rightarrow Z \nu_l\bar{\nu}_l $\end{document} via the production processes \begin{document}$ e^-e^+ \rightarrow ZH^* \rightarrow Z (H^* \rightarrow Z \nu_l\bar{\nu}_l) $\end{document}, including the initial beam polarizations at future lepton colliders. The Standard Model backgrounds, such as the processes \begin{document}$ e^-e^+ \rightarrow \nu_l\bar{\nu}_l ZZ $\end{document}, are also examined in this study. Numerical results indicate that one-loop corrections make contributions of approximately 10% to the decay rates. These are sizeable contributions and should be taken into account at future colliders. We show that the signals \begin{document}$ H\rightarrow Z\nu_l\bar{\nu}_l $\end{document} are clearly visible at the center-of-mass energy \begin{document}$ \sqrt{s}=250 $\end{document} GeV and are difficult to probe in higher-energy regions owing to the dominant backgrounds.     

Scalar dark matter and muon g-2 in a U(1)L_μ-L_τ model

We consider a simple scalar dark matter model within the frame of gauged L_μ→T_τ symmetry.A new gauge boson Z’,as well as two scalar fields S and Φ,are introduced to the Standard Model(SM),where S and Φ are SM singlets but both carry U(1)_{L_μ-L_τ} charge.The real component and imaginary component of S can acquire different masses after spontaneously breaking symmetry,and the lighter one can play the role of dark matter,which is stabilized by an extra Z₂ symmetry.We consider t...     

General SU(2)L × SU(2)R × U(1)EM Sigma Model with External Sources, Dynamical Breaking and Spontaneous Vacuum Symmetry Breaking

We give a general SU(2) _L × SU(2) _R × U(1) _EM sigma model with external sources, dynamical breaking and spontaneous vacuum symmetry breaking, and present the general formulation of the model. It is found that σ and π⁰ without electric charges have electromagnetic interaction effects coming from their internal structures. A general Lorentz transformation relative to external sources is derived, using the general Lorentz transformation and the four-dimensional current of nuclear matter of the ground state with J _gauge = 0, we give the four-dimensional general relations between the different currents of nuclear matter systems with J _gauge≠ 0 and those with J _gauge = 0. The relation of the density’s coupling with external magnetic field is derived, which conforms well to dense nuclear matter in a strong magnetic field. We show different condensed effects in strong interaction about fermions and antifermions, and give the concrete scalar and pseudoscalar condensed expressions of σ₀ and π₀ bosons. About different dynamical breaking and spontaneous vacuum symmetry breaking, the concrete expressions of different mass spectra are obtained in field theory. This paper acquires the running spontaneous vacuum breaking value σ′₀, and obtains the spontaneous vacuum breaking in terms of the running σ′₀, which make nucleon, σ and π particles gain effective masses. We achieve both the effect of external sources and nonvanishing value of the condensed scalar and pseudoscalar paticles. It is deduced that the masses of nucleons, σ and π generally depend on different external sources. PACA numbers: 24.10.-i, 11.30.Qc     

A non-renormalizable B-L model with Q4 × Z4 × Z2 flavor symmetry for cobimaximal neutrino mixing

We construct a non-renormalizable gauge \begin{document}$ B-L $\end{document} model based on \begin{document}$ Q_4\times Z_4\times Z_2 $\end{document} symmetry that successfully explains the cobimaximal lepton mixing scheme. Small active neutrino masses and both neutrino mass hierarchies are produced via the type-I seesaw mechanism at the tree-level. The model is predictive; hence, it reproduces the cobimaximal lepton mixing scheme, and the reactor neutrino mixing angle \begin{document}$ \theta_{13} $\end{document} and the solar neutrino mixing angle \begin{document}$ \theta_{12} $\end{document} can obtain best-fit values from recent experimental data. Our model also predicts the effective neutrino mass parameters of \begin{document}$ m_{\beta }\in (8.80, 9.05)\, \mathrm{meV} $\end{document} and \begin{document}$ \langle m_{ee}\rangle \in (3.65, 3.95)\, \mathrm{meV} $\end{document} for normal ordering (NO) and \begin{document}$ m_{\beta }\in (49.16, 49.21)\, \mathrm{meV} $\end{document} and \begin{document}$ \langle m_{ee}\rangle \in (48.59, 48.67)\, \mathrm{meV} $\end{document} for inverted ordering (IO), which are highly consistent with recent experimental constraints.     

Neutrino masses,leptonic flavor mixing,and muon(g−2)in the seesaw model with the U(1)Lμ-Lrgauge symmetry

The latest measurements of the anomalous muon magnetic moment a_μ≡(g_μ-2)/2show a 4:2σdiscrepancy between the theoretical prediction of the Standard Model and the experimental observations.To account for such a discrepancy,we consider a possible extension of the type-(I+II)seesaw model for neutrino mass generation with a gauged L_μ-L_rsymmetry.By explicitly constructing an economical model with only one extra scalar singlet,we demonstrate that the gauge symmetry U(1)L_μ-L_rand its spontaneous breaking are crucial not only for explaining the muon result but also for generating the neutrino masses and leptonic flavor mixing.Various phenomenological implications and experimental constraints on the model parameters are also discussed.     

Improved sensitivity to charged Higgs searches in top quark decays t→bH+→b(τ+ντ) at the LHC using τ polarisation and multivariate techniques

We present an analysis with improved sensitivity to the light charged Higgs (m_H⁺ < m_t-m_bm_{H^{+}} < m_{t}-m_{b}) searches in the top quark decays t→bH ⁺→b(τ ⁺ ν _τ )+c.c. in the t[`(t)]t\bar{t} and single t/[`(t)]t/\bar{t} production processes at the LHC. In the Minimal Supersymmetric Standard Model (MSSM), one anticipates the branching ratio B (H⁺ ?t⁺n_t) @ 1{\mathcal{B}} (H^{+} \to\tau^{+}\nu_{\tau})\simeq1 over almost the entire allowed tanb\tan\beta range. Noting that the τ ⁺ arising from the decay H ⁺→τ ⁺ ν _τ are predominantly right-polarized, as opposed to the τ ⁺ from the dominant background W ⁺→τ ⁺ ν _τ , which are left-polarized, a number of H ⁺/W ⁺→τ ⁺ ν _τ discriminators have been proposed and studied in the literature. We consider hadronic decays of the τ ^±, concentrating on the dominant one-prong decay channel τ ^±→ρ ^± ν _τ . The energy and p _T of the charged prongs normalised to the corresponding quantities of the ρ ^± are convenient variables which serve as τ ^± polariser. We use the distributions in these variables and several other kinematic quantities to train a boosted decision tree (BDT). Using the BDT classifier, and a variant of it called BDTD, which makes use of decorrelated variables, we have calculated the BDT(D)-response functions to estimate the signal efficiency vs. the rejection of the background. We argue that this chain of analysis has a high sensitivity to light charged Higgs searches up to a mass of 150 GeV in the decays t→bH ⁺ (and charge conjugate) at the LHC. For the case of single top production, we also study the transverse mass of the system determined using Lagrange multipliers.     

Theory of dynamic spin susceptibility in terms of the t-J-V model: Comparison with neutron scattering data for Pr0.88LaCe0.12CuO4 ? x and La2 ? xSrxCuO4

A formula for the dynamic spin susceptibility is derived in terms of the t-J-V model. This formula makes it possible to explain the main features of recent experiments on neutron scattering in the electron-doped superconductor Pr_0.88LaCe_0.12CuO_{4 − x} . In particular, the proposed theory reproduces well a V-shaped relief in the frequency behavior of the imaginary part χ″(Q, ω) of the susceptibility of the Pr_0.88LaCe_0.12CuO_{4 − x} compound in the vicinity of the wave vector Q = (π,π) and the scaling behavior of the position of the maxima in the dependence of the function χ″(Q, ω) T on the quantity ω/T. The magnetism of the high-temperature superconductors is dual. These materials contain charge carriers, on the one hand, and localized spins in the copper ion sublattice, on the other hand. Both these systems are strongly coupled to each other. The mode of collective oscillations is common. The magnetism of localized spins “freezes” with the appearance of the superconducting gap. The recently revealed double-peak structure of the imaginary part χ″(Q, ω) of the susceptibility in superconductors of the La_1.84Sr_0.16CuO₄ type is explained. The low-frequency absorption peak is located within the superconducting gap and interpreted as a manifestation of the branch of spin excitons, and the high-frequency absorption peak predominantly corresponds to renormalized collective oscillations of localized spins. Original Russian Text ? A.I. Andreev, I.M. Eremin, M.V. Eremin, 2009, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2009, Vol. 135, No. 1, pp. 65–76.     

Magnetic and band parameters of (3HgS)1–x(Al2S3)x (x = 0.5) crystals doped with manganese

Investigations of magnetic susceptibility (χ) of (3HgS)_1–x (Al₂S₃) _x (x = 0.5) crystals doped with manganese investigated by the Faraday method in the range of Т = 77–300 K and Н = 0.25–4 kOe demonstrate that peculiar magnetic properties can be due to the presence of clusters of the Mn–S–Mn–S type in these crystals. Based on the investigation of kinetic coefficients of the crystals performed for Т = 77–300 K and Н = 0.5–5 kOe, it is established that the crystals demonstrate conductivity of the n-type, and their electric conduction only very slightly depends on the temperature and shows a maximum, the Hall coefficient is independent of the temperature, while the temperature dependences of mobility exhibit a maximum. Using the concentration dependence of the effective electron mass at the Fermi level, the width of the forbidden band, the matrix element of interatomic interaction, and the effective mass on the conduction-band bottom are obtained. Based on investigations by optical methods, the presence of direct optical interband transitions in the crystals is established and the value of the optical forbidden band (at Т = 300 K) is determined.     

The Ratio Rdp of the quasielastic nd → p(nn) to the elastic np → pn charge-exchange-process yields at the proton emitting angle θp,lab = 0° over 0.55–2.0 GeV neutron-beam energy region. Comparison of the results with the model-dependent calculations

Our new experimental results (see, e.g., Preprint JINR no. E1-2008-61 (Dubna, 2008)) on ratio R _dp of the quasielastic charge-exchange yield at the proton emitting angle θ _p,lab = 0° for the nd → p(nn) reaction to the elastic np → pn charge-exchange yield were presented. The measurements were carried out at the Nuclotron of the Veksler and Baldin Laboratory of High Energies of the JINR (Dubna) at the neutron-beam kinetic energies of 0.55, 0.8, 1.0, 1.2, 1.4, 1.8, and 2.0 GeV. In this paper the comparison of the experimental R _dp data with the obtained R _dp calculations within the impulse approximation by using the invariant-amplitude sets from the GW/VPI phase-shift analysis is made. The R _dp values calculated using the set of invariant amplitude data for the elastic np → pn charge exchange at θ _p,CM = 0°, agree with the experimental data. This confirmed the nd → p(nn) process yield at θ _p,CM = 0° is caused by the contribution of the spin-dependent part of the elastic np → pn charge-exchange reaction. Thus, it has been shown that the obtained experimental R _dp results can be used for the Delta-Sigma experimental program to reduce the total ambiguity in the extraction of the amplitude real parts. The text was submitted by the authors in English.     

Dielectric spectroscopy of PbZr1 ? xTixO3 solid solutions (0.495 ≤ x ≤ 0.51) in a temperature range of 100–300 K at frequencies from 1 × 10?2 to 2 × 107 Hz

The behavior of the relative permittivity ɛ/ɛ₀ of PbZr_{1 − x} Ti _x O₃ (PZT) solid solutions (0.495 ≤ x ≤ 0.51) in the temperature range of 100–300 K at frequencies from 1 × 10⁻² to 2 × 10⁷ Hz was investigated. Diffuse, strongly relaxing maxima at T = 230−260 K (x = 0.495−0.505) and 150–160 K (x = 0.510) were observed in the PZT studied. The relaxation processes are well described by the Vogel-Fulcher law, and the dielectric spectra are approximated by the Cole-Cole formula.