Leptonic Weak Interactions Research Articles

Numerical simulation of the hydrodynamical combustion to strange quark matter in the trapped neutrino regime

We simulate and study the microphysics of combustion (flame burning) of two flavored quark matter (u,d) to three flavored quark matter (u,d,s) in a trapped neutrino regime applicable to conditions prevailing in a hot proto-neutron star. The reaction–diffusion–advection equations for (u,d) to (u,d,s) combustion are coupled with neutrino transport, which is modeled through a flux-limited diffusion scheme. The flame speed is proportional to initial lepton fraction because of the release of electron chemical potential as heat, and reaches a steady-state burning speed of (0.001–0.008)c. We find that the burning speed is ultimately driven by the neutrino pressure gradient, given that the pressure gradient induced by quarks is opposed by the pressure gradients induced by electrons. This suggests, somewhat counter-intuitively, that the pressure gradients that drive the interface are controlled primarily by leptonic weak decays rather than by the quark Equation of State (EOS). In other words, the effects of the leptonic weak interaction, including the corresponding weak decay rates and the EOS of electrons and neutrinos, are at least as important as the uncertainties related to the EOS of high density matter. We find that for baryon number densities nB≤0.35 fm−3, strong pressure gradients induced by leptonic weak decays drastically slow down the burning speed, which is thereafter controlled by the much slower burning process driven by backflowing downstream matter. We discuss the implications of our findings to proto-neutron stars.

A TORSIONAL MODEL OF LEPTONS

Quite recently it was shown that torsion induces interactions among leptons that are identical to the weak interactions of leptons of the Weinberg Standard Model, if it is in terms of leptonic bound states that the bosonic sector is built; here we obtain the partially conserved axial currents showing that they are the same of the Standard Model, if the composite mediators have specific mass relationships: we show that their masses are indeed the measured ones, if reasonable approximations are taken.

Neutrino–nucleus reactions with the relativistic quasiparticle RPA

We introduce a novel theoretical framework for the description of weak interaction rates in reactions of leptons with finite nuclei. The weak interaction of leptons with hadrons is expressed in the standard current–current form, the nuclear ground state is described with the relativistic Hartree–Bogoliubov model and the relevant transitions to excited states are calculated in the relativistic quasiparticle random phase approximation. The model is tested for electron– and muon–neutrino reactions on 12C, in a study of cross sections averaged over experimental neutrino fluxes. Using 56Fe as an example, it is shown that at higher neutrino energies the inclusion of spin-dipole transitions, and also excitations of higher multipolarities, is essential for a quantitative description of neutrino–nucleus cross sections.

New invariance in electroweak standard model and conservation of helicity

The Lagrangian of the electroweak standard model is invariant under the chirality transformation of fermionic fields and reversal of the Higgs field. This invariance implies the conservation of helicity in weak interaction processes. The application to leptonic weak interaction is discussed in detail.

Light neutrinos, nonuniversality of the leptonic weak interaction and a fourth massive generation

Neutrinos are massless, charged leptons light due to the presence of a degenerate heavy family. The masses of the light leptons imply nontrivial mixing effects, leading to a slight nonuniversality in the τ-channel, neutrino conversion in the v μ -v τ system and radiative decays of the charged leptons.

Leptonic tau decays: How to determine the Lorentz structure of the charged leptonic weak interaction by experiment.

The purely leptonic decays ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\nu}}_{\ensuremath{\mu}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ and ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\nu}}_{e}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ are both described by the most general (local, derivative-free, lepton-number-conserving) four-fermion interaction Hamiltonian characterized by ten complex coupling constants. The $V\ensuremath{-}A$ hypothesis of the standard model can be proven experimentally, as has been done for $\ensuremath{\mu}$ decay, from the results of only five key experiments. These five $\ensuremath{\tau}$ decay experiments would determine upper limits for all eighteen non-($V\ensuremath{-}A$) terms and a lower limit for the $V\ensuremath{-}A$ coupling. Most of these experiments can be carried out at an ${e}^{+}{e}^{\ensuremath{-}}$ collider with unpolarized beams near $\ensuremath{\tau}$ pair production threshold as well as in the region of the $\ensuremath{\Upsilon}$ resonances. Analytical decay distributions are derived in terms of suitable laboratory observables. With their help statistical errors for the decay parameters ${\ensuremath{\rho}}_{e}$, ${\ensuremath{\eta}}_{e}$, ${\ensuremath{\delta}}_{e}$, ${\ensuremath{\xi}}_{e}$, ${\ensuremath{\rho}}_{\ensuremath{\mu}}$, ${\ensuremath{\eta}}_{\ensuremath{\mu}}$, ${\ensuremath{\delta}}_{\ensuremath{\mu}}$, ${\ensuremath{\xi}}_{\ensuremath{\mu}}$, ${\ensuremath{\xi}}_{\ensuremath{\pi}}$, and ${\ensuremath{\xi}}_{K}$ are calculated assuming an ideal detector. For ${10}^{7}$ produced ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ pairs these errors are in the range of (2-20)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ except the error for ${\ensuremath{\eta}}_{e}(\ensuremath{\Delta}{\ensuremath{\eta}}_{e}=0.53)$. The parameters $\ensuremath{\rho}$ and $\ensuremath{\eta}$ that describe the isotropic part of the spectrum are found to be strongly correlated. Therefore any experiment should be analyzed simultaneously with respect to both parameters. An experimental value of ${\ensuremath{\eta}}_{\ensuremath{\mu}}$ is required for the derivation of the Fermi coupling constant for the muonic decay. By measuring the ${\ensuremath{\mu}}^{+}$ polarization from ${\ensuremath{\tau}}^{+}$ decay the polarization parameter ${\ensuremath{\xi}}_{\ensuremath{\mu}}^{\ensuremath{'}}$ can be deduced with an error of 15%. The measurements of ${\ensuremath{\xi}}_{e}$ and ${\ensuremath{\delta}}_{e}$ will allow us to constrain five of the ten complex coupling constants for the decay ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\nu}}_{e}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ the measurements of ${\ensuremath{\xi}}_{\ensuremath{\mu}}$, ${\ensuremath{\delta}}_{\ensuremath{\mu}}$, and ${\ensuremath{\xi}}_{\ensuremath{\mu}}^{\ensuremath{'}}$ will even constrain eight complex coupling constants for the decay ${\ensuremath{\tau}}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\nu}}_{\ensuremath{\mu}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$. The determination of the remaining coupling constants would require the measurement of the cross section for the inverse decay ${\ensuremath{\nu}}_{\ensuremath{\tau}}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{\ensuremath{-}}{\ensuremath{\nu}}_{e}$ or of correlations between one of the neutrinos and the ${\ensuremath{\mu}}^{+}$ or ${\ensuremath{\tau}}^{+}$ for the muonic decay.

Leptonic CP violating asymmetries in Z 0 decays

We show that CP conservation may be violated in the leptonic decays of the Z 0 to a level that may be probed at LEP. We find that there may exist decay asymmetries η ij= BR( Z 0→ e i+ e j )− BR( Z 0→ e j+ e i ) as large as O(10 −7–10 −8), where one of the charged leptons is a τ and the other is an e or μ. Such a value is consistent with all information about neutrino physics and the structure of the leptonic weak interaction and could arise in a simple extension of the standard SU(2) ⊗ U(1) model.

Symmetry tests with highly charged ions

We summarize the present status of testing the standard model of parity nonconservation in neutral atoms, emphasizing the success in understanding the semileptonic weak interactions. There is good agreement for the nuclear spin independent contributions, especially in cesium. There is some evidence of nuclear spin dependent terms, probably due to hadronic weak interactions. There is no evidence of leptonic weak interactions. The lessons learned from atomic physics are discussed, together with strategies for parity experiments using highly charged ions.

Weak Interactions of Leptons and Quarks

<i>Weak Interactions of Leptons and Quarks</i>

Muon decay: Measurement of the positron polarization and implications for the spectrum shape parameter η, V-A and T-invariance

A new measurement of the longitudinal polarization P L of the e + from μ + decay is presented here. Combined with our previously published result, we obtain P L = 0.998 ± 0.045 (statistical plus systematic error). We also report on the first measurement of P L( θ) where θ is the angle between the e + line of flight and the μ + polarization. The implications on the “low energy spectrum shape parameter η″, on the ratio of A coupling to V coupling and on time-reversal are discussed. The results are in agreement with the standard V-A form of the charged leptonic weak interaction.

Leptonic charged weak interactions in the left-right symmetric model

An extensive analysis of the charged weak interactions of leptons within the left-right symmetric electroweak model is made. A general mass matrix of the neutrinos is allowed for, neglecting intergenerational mixing for simplicity, and the limits to the parameters of the model are obtained for various possible neutrino mass configurations. It is also pointed out that one of the muon decay parameters, δ, can uniquely distinguish between the different possibilities for the masses of the right-handed neutrinos.

Experiments in the gauge revolution

Weak Interactions of Leptons and Quarks. By E.D. Commins and P.H. Bucksbaum. Cambridge University Press: 1983. Pp.473. Hbk £37.50, $69.50; pbk £16.50, $27.95.

Does the positron from muon decay have transverse polarization?

The transverse polarization of the e + in μ + decay has been measured for the first time. This measurement allows the initial determination of the four μ decay parameters: α A and β A [with their linear combination η = (α − 2β) A ] plus, as the first direct measurement of time reversal noninvariant parameters in a purely leptonic interaction, α′ A and β′ A . The results are consistent with zero and in agreement with the standard V - A form of the charged leptonic weak interaction.

Study of the V, a structure of the charged leptonic current

Although the charged weak interactions of leptons are conventionally described by pure V - A currents, several recent models have mechanisms which admit components of other structures. It is therefore becoming increasingly important to know the experimentally allowed amounts of V + A (as well as S, P, and T) admixture. In this paper the structure of the charged leptonic weak currents is studied in the framework of two models, the fermion-mirror fermion mixing model connected with many grand unification schemes, and the left-right symmetric SU(2) L × SU(2) R × U(1) flavor model. Both of these models allow more general V, A structure of the currents. We fit the parameters of these models to experimental data from pseudoscalar meson decay, muon decay, nuclear β-decay, and inverse muon decay. We find that substantial departure from pure V - A is allowed, the best fit values of the parameters being within one standard deviation from their V - A values. In the mixing model, different mass configurations of the mirror neutrinos are considered. The case with a heavy (> m K) electron mirror neutrino and a light (⪡ m e) muon mirror neutrino is disfavored by the fit. The lower limit of the mass of the right-handed gauge boson W R in the SU(2) L × SU(2) R × U(1) model is m(W R) >3.4 m(W L) (68.3% c.l.). The left-right symmetric model fits slightly better than the mixing model. The only data explicitly disagreeing with the V - A model is the ξ-parameter in muon decay. It would be of great importance to have this parameter remeasured.

Experimental test of electroweak effects at PETRA energies

The differential cross sections for Bhabha scattering and μ pair production, and the total τ pair cross section as measured by the PLUTO detector at PETRA, have been analyzed to extract information on the weak interaction of leptons. The data are compared with unified gauge theories. Since the observed electroweak effects are still consistent with zero (within errors) we can set experimental limits on neutral current parameters atQ2 values of 950 GeV2. In the framework of the standard SU(2)×U(1) model we find sin2Θ w <0.52(95% c.l.). In the context of general singleZo models we can excludeZo masses of less than 40 GeV.

FlavourSU 3×U 1 gauge model with fundamental triplets and singlets

ASU3×U1 gauge model for the electromagnetic and weak interactions of leptons and quarks is suggested as an extension of a pureSU3 model for leptons, proposed in a previous paper, yielding a fixed Weinberg angle of 30°. The essential features of the leptonic model remain unchanged. The angle relating the coupling strengthsg.g′ of theSU3—and theU1—gauge bosons in the conventional sector merely rescales the coupling constantg and the W-boson mass. Within the experimental errors the model accommodates the data on neutrino scattering. It yields relative bounds for the masses of the gauge bosons. Absolute bounds for the mass ratios can be derived from experimental data.

Exchange Currents, Isobaric Excitations and the Deuteron

AbstractSome recent attempts to take into account exchange currents and isobaric excitations in the electromagnetic and weak interactions of leptons with the deuteron are reviewed. After a presentation of the relevant theoretical framework the crucial experiments supporting strongly the exchange current ideas are discussed in some detail.

Theory of pure leptonic weak interaction with induced shadow states

By making use of the ε-splitting mechanism to define weak currents we construct a renormalizable theory in terms of the current-current interaction for pure leptonic weak interaction. The presence of the shadow states induced by the current-current interaction due to the ε-splitting mechanism makes, after a primary mass and wave function renormalization, the theory finite in perturbative calculations. The theory involves, in addition to the physical lepton masses, the charged current-current interaction coupling constantG c and the neutral current-current coupling constantG N. The computations for muon decay and neutrino-electron scattering processes in chain approximation show that our formalism is not ruled out in comparison with the experimental data available at the present time.

Dual Models of Weak Interactions of Leptons and Quarks

Composite models of leptons and quarks have heen considered on a hypothesis of lepton­ quark symmetry. This hypothesis leads us to the dual models of weak interactions of leptons and quarks. Some experimental tests to the weak duality in high energy lepton reaction will be proposed.

Muon-neutrino electron scattering in the theory of pure leptonic weak interaction with induced shadow states

With in the framework of the theory of shadow states (x), a finite theory for pure leptonic weak interact ion (2) was proposed before by WANG and by one of the present authors (CHIA~G). However, the theory is not sat isfactory mainly for two reasons: 1) neutral currents are not included, 2) since the shadow masses are free parameters in the theory, i t is aesthetical ly not appealing. Recently (s) i t has been observed tha t for the 4-fermion self-interaction, the current with point spl i t t ing would induce indefinite-metric states which are effectively equivalent to the shadow states in the finite quantum electrodyuamics proposed by AReas, HAN and SUD~SHAN (4), and by CHIA.~G and GL~.SO.~ (5) and also to the shadow states in the finite theory for the pure leptonic weak interact ion above-mentioned. The shadow masses are uniquely re la ted to the current-current coupling constant . By making use of the point-spl i t t ing mechanism, we have proposed (s) a finite theory for pure leptonic weak interact ion including neutral currents. In this approach the neutral currents play a crucial role in connection with the finiteness of the theory. The shadow states are induced by the neutral current self-interaction, and the theory involves only two parameters , the charged current coupling constant and the neutralcurrent coupling constant. In this note we present our computa t ion for the elast ic-scattering processes e -~a(~a) -~e-+-~(+~) . The result of our computat ion shows tha t our theory is compatible with the exper imenta l da ta available at present. To s tar t with, let us recall the in teract ion Lagrangian in ref. (6).