Weak radiative decays of hyperons within theSU(6) broken quark-diquark model

In view of persisting discrepancy between experimental and theoretical results, specially in the weak radiative decays of∑ ⁺ andΞ ⁰, we analyse these decays within the framework of the QCD inspired quark-diquark model. On introducing a slightSU(6) breaking we obtainα(∑ ⁺→p+γ)≈?0.9 which is in excellent agreement with experimental value. Other decays are also improved in this scheme.     

One-loop electroweak corrections for polarized Møller scattering at different renormalization schemes and conditions

Using two different approaches, we perform detailed calculations of the one-loop (Next-to-Leading Order (NLO)) electroweak radiative corrections to the parity violating e ^? e ^? → e ^? e ^?(γ) scattering asymmetry. First approach, more classical, relies on calculations “by hand” with reasonable approximations, second approach relies on program packages FeynArts, FormCalc, LoopTools, and FORM. The detailed numerical analysis of the various contributions is provided for a wide range of energies relevant for the ultraprecise 11 GeV MOLLER experiment planned at the JLab, as well as future experiments at the International Linear Collider (ILC). The numerical results obtained within the on-shell renormalization scheme using two different sets of renormalization conditions are in excellent agreement. We also calculate the total NLO correction in the Constrained Differential Renormalization (CDR) scheme. Analysis of the results, along with the increasing experimental precision, shows that it is feasible that the corrections at the Next-to-Next-to-Leading Order (NNLO) level may be important for the next generation of experiments.     

Measurements of the radiative widths of the first T = 1, 2+ state of 20Ne and their relationship to analog β-decays

The radiative widths for decays of the ²⁰Ne T = 1, 2⁺ (10.27 MeV) state were measured by resonance α-capture in the reaction ¹⁶O(α, γ)²⁰Ne. A special windowless gas-cell target yielded a low-background spectrum enabling six γ-branches to be observed with a Ge(Li) detector. The six branches correspond to decays from the 10.27 MeV level to the following levels: 2⁺(7.83 MeV), 2⁺(7.42 MeV), 3^?(5.62 MeV), 2^?(4.97 MeV), 2⁺(1.63 MeV) and 0⁺(g.s.). The branching ratios and radiative widths Γ_γ to these levels are: 7.83 MeV [(0.22 ± 0.06)%, 0.008 ± 0.002 eV], 7.42 MeV [(6.9 ± 0.4)%, 0.31 ± 0.04 eV], 5.62 MeV [(2.1 ± 0.2)%, 0.097 ± 0.014 eV], 4.97 MeV [(1.3 ± 0.1)%, 0.060 ± 0.008 eV], 1.63 MeV [(88.9 ± 0.5)%, 4.08 ± 0.43 eV] and 0.0 MeV [(0.64 ± 0.14)%, 0.029 ± 0.008 eV]. The radiative widths to the 1.63 MeV and 7.42 MeV levels are used to determine the CVC predictions of the weak magnetism form factors and their effects on certain β-decay observables are evaluated.     

Charmonium States in QCD-Inspired Quark Potential Model Using Gaussian Expansion Method

We investigate the mass spectrum and electromagnetic processes of charmonium system with the nonperturbative treatment for the spin-dependent potentials, comparing the pure scalar and scalar-vector mixing linear confining potentials. It is revealed that the scalar-vector mixing confinement would be important for reproducing the mass spectrum and decay widths, and therein the vector component is predicted to be around 22?%. With the state wave functions obtained via the full-potential Hamiltonian, the long-standing discrepancy in M1 radiative transitions of J/ψ and ψ′ are alleviated. This work also provides an inspection and suggestion for the possible cc? states among the copious higher charmonium-like states. Particularly, the newly observed X(4160) and X(4350) are found in the charmonium family mass spectrum as M(2¹ D ₂)?= 4164.9 MeV and M(3³ P ₂)?= 4352.4 MeV, which strongly favor the J ^PC ?=?2^?+, 2⁺⁺ assignments respectively. The corresponding radiative transitions, leptonic and two-photon decay widths have been also predicted theoretically for the further experimental search.     

Symmetry breaking schemes and radiative decays of vector mesons

We have studied a hierarchy of SU(3) breaking schemes for the radiative decays of the vector mesons. In all of the four models we examine in detail, we find it hard to reconcile the newly measured radiative widths of ? → πγ, $\text{K}{}^{01}\text{→ K}{}^0\text{γ}$, φ → πγ, and φ → ηγ with the older measurements and upper bounds on other radiative rates. In particular we have difficulty in understanding the narrow radiative width of ?. A possible extension to an SU(4) symmetry breaking scheme is also suggested.     

Fermion masses generated by radiative corrections in aSU(2) L ×SU(2) R ×U(1) B-L model

A new model based on aSU(2) ^R ×SU(2) ^L ×U(1) ^B-L gauge symmetry group is presented. Fermion masses are generated by radiative corrections.     

Determination of the radiative lifetime of the d3Πg state of the C2 molecule by the laser-pyrolysis technique. A feasibility study

The feasibility is studied of using the laser-pyrolysis technique for determination of the radiative lifetimes of molecules.Measurements of time-resolved spectral emission were made on spatially resolved sections of the luminous plume produced by laser illumination of a graphite target in a vacuum. The nature of certain emission continua was investigated. The effects on C₂ Swan band emission of focal spot size, illumination power density, height and width of the plasma section observed and its distance from the target were studied. Conditions were determined for measuring physically significant radiative lifetimes for the d³Π_g, v=0 and v=1 levels, of C₂. In particular, the laser flux used was 3.8×10⁸W-cm^?2 while observations were made of a plume section from 0.5 to 0.7 mm from the target. The results, τ(0,0)=235±20 ns, τ(0,1)=250±20 ns, τ(1,0)=255±20 ns, are compared with those obtained by other methods. They are in good agreement with results obtained by pulsed electron excitation. Analysis of the experimental conditions in previous experiments using the laser-pyrolysis technique for measuring τ(d³Π_g of C₂ shows that they could not have lead to meaningful results of purely molecular properties.     

Strong radiative corrections to annihilations of quarkonia in QCD

The significance of the lowest-order QCD prediction for the annihilations of heavy quark-antiquark bound states is analyzed. The calculation of the leading strong radiative corrections to the hadronic versus electromagnetic annihilation rate ratio R of pseudoscalar quarkonium is presented. In terms of the coupling constant α_s, as defined in the minimal subtraction scheme, we find R = R⁽⁰⁾(1 + 22.14α_s/π). The physical significance of this result is discussed by comparing it with the calculation of the non-leading effects in α_s on the scaling violations in deep inelastic scattering. A bad convergence of the relative perturbative expansion is found, demanding for its safe application a value of the relevant momentum definitely higher than that of charmonium physics.     

Numerical Solution of Dyson Brownian Motion and a Sampling Scheme for Invariant Matrix Ensembles

The Dyson Brownian Motion (DBM) describes the stochastic evolution of N points on the line driven by an applied potential, a Coulombic repulsion and identical, independent Brownian forcing at each point. We use an explicit tamed Euler scheme to numerically solve the Dyson Brownian motion and sample the equilibrium measure for non-quadratic potentials. The Coulomb repulsion is too singular for the SDE to satisfy the hypotheses of rigorous convergence proofs for tamed Euler schemes (Hutzenthaler et al. in Ann. Appl. Probab. 22(4):1611–1641, 2012). Nevertheless, in practice the scheme is observed to be stable for time steps of O(1/N ²) and to relax exponentially fast to the equilibrium measure with a rate constant of O(1) independent of N. Further, this convergence rate appears to improve with N in accordance with O(1/N) relaxation of local statistics of the Dyson Brownian motion. This allows us to use the Dyson Brownian motion to sample N×N Hermitian matrices from the invariant ensembles. The computational cost of generating M independent samples is O(MN ⁴) with a naive scheme, and O(MN ³logN) when a fast multipole method is used to evaluate the Coulomb interaction.     

Properties of quark matter governed by quantum chromodynamics (II). Renormalization schemes in quark matter

Renormalization schemes are examined (in the Coulomb gauge) for quantum chromodynamics in the presence of quark matter. We demand that the effective coupling constant for all schemes become congruent with the vacuum QCD running coupling constant as the matter chemical potential, μ, goes to zero. Also, to enable us to standardize with the vacuum QCD running coupling constant at some asymptotic momentum transfer, $\text{|}\text{p}{}_0\text{|,}\text{we keep}\text{μ ? ¦}\text{p}{}_0\text{¦}$, to ensure that the matter contribution is negligible at this point. This means all schemes merge with vacuum QCD at $\text{|}\text{p}{}_0\text{|}$ and beyond. Two renormalization group invariants are shown to emerge: (i) the effective or invariant charge, g_inv², which is, however, scheme dependent and (ii) g²(M)/S(M), where S(M)^?1 is the Coulomb propagator, which is scheme independent. The only scheme in which g_inv² is scheme independent and identical to g²(M)/S(M) is the screened charged scheme (previous paper) characterised by the normalization of the entire Green function, S^?1, to unity. We conclude that this is the scheme to be used if one wants to identify with the experimental effective coupling in perturbation theory. However, if we do not restrict to perturbation theory all schemes should be allowed. Although we discuss matter QCD in the Coulomb gauge, the above considerations are quite general to gauge theories in the presence of matter.     

Calculation method for the continuum states of atomic systems

In the present work, we develop a calculational method of solving the scattering equations for spherically symmetric potentials by expanding the solutions on Coulomb functions. We utilize a multistep integration scheme together with the standard partial wave analysis in a region where the potential term dominates. The method applies to any physical problem expressed as [? ² + V(r) + k ²]ψ(r) = 0, while the extension of the method to more general scattering problems is briefly discussed. At present, we demonstrate a two-step Coulomb-fitted integration scheme by calculating the short-range scattering phase shifts for various potentials V (r).     

Radiative neutrino decay and the unusual X-ray flux from Sn 1987A

The radiative neutrino decay in the mass and a lifetime range, m_v=10–100 keV and τ_v=10³–10⁵ s, is often argued to be forbid by γ-ray data from past supernovas. We demonstrate that this argument is not always correct, and accordingly attempt to explain via radiative neutrino decay the unusual soft component of the X-ray spectrum from SN 1987A, observed by the satellite Ginga. Our fit to the data suggests that τ_v=(1–3)×10⁴s·(m_v/50 keV).     

Radiative quark masses constrained by the gauge group only

We discuss the possibility of obtaining the observed pattern of quark masses and mixings as a consequence of radiative corrections, gauge invariance and particle content of the theory. We do not allow any kind of additional symmetry, such as family and discrete symmetries. A model based on the gauge groupSU(3)×SU(2) _L ×SU(2) _R ×U(1) _B?L is considered. It turns out that the correct values of quark masses can be reasonably reproduced. The typical strength of the flavour changing couplings of theZ ⁰-boson is however at least one order of magnitude above the experimental upper bounds. A comparison is made with a model in which an additional discrete symmetry is present. In this case flavour changing phenomena can be kept under control.     

Search for exotic baryons with hidden strangeness in proton diffractive production at the energy of 70 GeV

The first preliminary results from the upgraded SPHINX spectrometer, working in the proton beam with the energy of 70 GeV of the IHEP accelerator, are presented. The data for the reaction p + N ? [Σ⁰ K ⁺] + N based on new statistics are in good agreement with our previous data and strongly support the existence of the X (2000) state (with an increase in statistics for this state by a factor of ～5). We also observed radiative decay of Λ(1520) → Λγ. The significant increase in statistics for many diffractive-production reactions will allow us to study them in great detail.     

A minimalSU(2)×U(1)×U(1) electroweak model with mirror fermions

We present a minimal extension of the standard electroweak model, which accommodates mirror fermions, based onSU(2)×U(1)×U(1). Mirror mixing happens through sterile neutrino states and induces radiative mixing for charged leptons. Quarks and mirror quarks are not mixed with each other, consistent with the suppression of flavour changing neutral currents. Higgs sector, fermion masses and neutral currents are discussed. In this scheme there can be a secondZ boson as light as 0.2TeV.     

Spatial differencing of the discrete ordinate equations in optically thick media

We present a modification to the linear characteristic method used to finite difference the discrete ordinate (S-N) equations. This modification is designed to produce the correct diffusion limit in the radiative transfer context in the limit of optically thick mesh cells. Numerical tests suggest that this finite difference method is a practical calculational scheme for radiative transfer problems.     

Second order electromagnetic radiative corrections toe + e −→γ*Z 0→μ+μ−

We derive a compact expression for the cross sectione ⁺ e ^?→μ⁺μ^?, containing a full treatment of the electromagnetic radiative corrections from both initial and final states. By using a formulation in terms of evolution equations, we obtain an expression for the cross-section to theO(α²) which includes soft and hard photons and resums to all orders dominant and non-dominant logarithmic contributions. Comparisons with previous results are made.     

Semiphenomenological approximation of the sums of experimental radiative strength functions for dipole gamma transitions of energy E γ below the neutron binding energy B n for mass numbers in the range 40 ≤ A ≤ 200

The sums of radiative strength functions for primary dipole gamma transitions, k(E1) + k(M1), are approximated to a high precision by a superposition of two functional dependences in the energy range 0.5 < E ₁ < B _n ? 0.5 MeV for the ⁴⁰K, ⁶⁰Co, ^71,74Ge, ⁸⁰Br, ¹¹⁴Cd, ¹¹⁸Sn, ^124,125Te, ¹²⁸I, ^137,138,139Ba, ¹⁴⁰La, ¹⁵⁰Sm, ^156,158Gd, ¹⁶⁰Tb, ^163,164,165Dy, ¹⁶⁶Ho, ¹⁶⁸Er, ¹⁷⁰Tm, ¹⁷⁴Yb, ^176,177Lu, ¹⁸¹Hf, ¹⁸²Ta, ^{183,184,185,187}W, ^{188,190,191,193}Os, ¹⁹²Ir, ¹⁹⁶Pt, ¹⁹⁸Au, and ²⁰⁰Hg nuclei. It is shown that, in any nuclei, radiative strength functions are a dynamical quantity and that the values of k(E1) + k(M1) for specific energies of gamma transitions and specific nuclei are determined by the structure of decaying and excited levels, at least up to the neutron binding energy B _n .     

A grand unified theory based onSU(n, 1)-minimal supergravity

We discuss a grand unified theory in the framework ofSU(n, 1) minimal supergravity with the Planck mass as the only input mass scale.M _W ≈m _3/2 is fixed by radiative corrections to be naturally ?M _P1. Due to the particular form of explicit soft supersymmetry breaking a light singlet can be used to obtain naturally light Higgs doublets and for a new mechanism for radiativeSU (2)×U(1) breaking. The low energy particle spectrum is very restricted withm _3/2≈10⁴ GeV.