共查询到20条相似文献,搜索用时 15 毫秒
1.
We consider the τ leptonic decay $\tau\rightarrow
l\bar{\nu}_{l}\nu_{\tau}$ in the framework of the littlest
Higgs (LH) model and calculate the corrections of new particles to
this decay. We find that the contributions of the charged scalars
can be safely ignored and the LH model is in perfect agreement
with the universality of the couplings of the SU gauge bosons
to the leptonic charged currents. The corrections of the LH model
to the τ leptonic decay $\tau\rightarrow
l\bar{\nu}_{l}\nu_{\tau}$ are not sensitive to the parameter
c, but depend strongly on the parameters f and x. The
precision measured data about the τ leptonic decay demand
that the parameter f approximately equal 3.5 TeV and x>0.1, while agree with the general expectation based on other
phenomenological
explorations. 相似文献
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4.
R. Barate et al. 《The European Physical Journal C - Particles and Fields》2001,19(2):213-227
5.
An upper limit for the –neutrino mass has been determined from the decay using data collected with the OPAL detector from 1991 to 1995 in collisions at . A limit of 43.2 MeV at 95% CL is obtained using a two–dimensional method in the invariant mass and energy distribution from 22 selected events. Combining this result with OPAL's previously published measurement
using decays, a new combined limit of MeV (95% CL) is obtained.
Received: 15 April 1998 / Published online: 12 August 1998 相似文献
6.
The fermionic and bosonic sectors of the 2-site Hubbard model have been exactly solved by means of the equation of motion and Greens function formalism. The exact solution of the t-J model has been also reported to investigate the low-energy dynamics. We have successfully searched for the exact eigenoperators, and the corresponding eigenenergies, having in mind the possibility to use them as an operatorial basis on the lattice. Many local, single-particle, thermodynamical and response properties have been studied as functions of the external parameters and compared between the two models and with some numerical and exact results. It has been shown that the 2-site Hubbard model already contains the most relevant energy scales of the Hubbard model: the local Coulomb interaction U and the spin-exchange one
. As a consequence of this, for some relevant properties (kinetic energy, double occupancy, energy, specific heat and entropy) and as regards the metal-insulator transition issue, it has resulted possible to almost exactly mime the behavior of larger systems, sometimes using a higher temperature to get a comparable level spacing. The 2-site models have been also used as toy models to test the efficiency of the Greens function formalism for composite operators. The capability to reproduce the exact solutions, obtained by the exact diagonalization technique, gives a firm ground to the approximate treatments based on this formalism.Received: 16 July 2003, Published online: 30 January 2004PACS:
71.10.-w Theories and models of many-electron systems - 71.10.Fd Lattice fermion models (Hubbard model, etc.) 相似文献
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9.
D. Bardin 《The European Physical Journal C - Particles and Fields》2002,24(3):373-383
We study predictions for the reaction . The complete one-loop corrections are taken into account and higher order contributions, in particular those for the observed
real photons, are added whenever necessary. The event generator MC, a general-purpose Monte Carlo generator for the process based on the method of exclusive exponentiation, is used as the environment. We extend its applicability to the process ,, where the observation of at least a single is required. The exponentiation is implemented in much the same way as for the s-channel process alone. In particular, all photonic effects present in the case of W exchange, which cannot be included in the s-channel exponentiation scheme, are calculated to a finite order only. The real hard photon matrix element is calculated up
to . Leading logarithmic contributions of the two-loop corrections and one-loop photonic corrections accompanying real single-photon
emission are included. The electroweak corrections are calculated with the DIZET library of the ZFITTER package. Numerical
tests and predictions for typical observables are presented.
Received: 30 October 2001 / Revised version: 5 March 2002 / Published online: 22 May 2002 相似文献
10.
The DELPHI Collaboration J. Abdallah et al. 《The European Physical Journal C - Particles and Fields》2003,28(1):15-26
Searches for resonant production in e
+
e
-
collisions under the assumption that R-parity is not conserved and that the dominant R-parity violating coupling is or used data recorded by DELPHI in 1997 to 2000 at centre-of-mass energies of 183 to 208 GeV. No deviation from the Standard
Model was observed. Upper limits are given for the and couplings as a function of the sneutrino mass and total width. The limits are especially stringent for sneutrino masses equal
to the centre-of-mass energies with the highest integrated luminosities recorded.
Received: 14 January 2003 / Published online: 14 March 2003 相似文献
11.
We study the complex Berry phases in non-Hermitian systems with parity- and time-reversal $\left({ \mathcal P }{ \mathcal T }\right)$ symmetry. We investigate a kind of two-level system with ${ \mathcal P }{ \mathcal T }$ symmetry. We find that the real part of the the complex Berry phases have two quantized values and they are equal to either 0 or π, which originates from the topology of the Hermitian eigenstates. We also find that if we change the relative parameters of the Hamiltonian from the unbroken-${ \mathcal P }{ \mathcal T }$-symmetry phase to the broken-${ \mathcal P }{ \mathcal T }$-symmetry phase, the imaginary part of the complex Berry phases are divergent at the exceptional points. We exhibit two concrete examples in this work, one is a two-level toys model, which has nontrivial Berry phases; the other is the generalized Su–Schrieffer–Heeger (SSH) model that has physical loss and gain in every sublattice. Our results explicitly demonstrate the relation between complex Berry phases, topology and ${ \mathcal P }{ \mathcal T }$-symmetry breaking and enrich the field of the non-Hermitian physics. 相似文献
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Acoustical Physics - 相似文献
14.
Search for pair-produced leptoquarks in e + e- interactions at $\sqrt{s} \simeq 189\text{--}209$ GeV
A search for pair-produced leptoquarks is performed using
collision events collected by the OPAL detector at LEP at centre-of-mass energies between 189 and 209 GeV. The data sample corresponds to a total integrated luminosity of 596 pb-1. The leptoquarks are assumed to be produced via couplings to the photon and the Z0. For a given search channel only leptoquark decays involving a single lepton generation are considered. No evidence for leptoquark pair production is observed. Lower limits on masses for scalar and vector leptoquarks are calculated. The results improve most of the LEP limits derived from previous searches for the pair production process by 10-25 GeV, depending on the leptoquark quantum numbers.Received: 6 May 2003, Published online: 24 October 2003 相似文献
15.
In case of chiral U
A(1) symmetry restoration the mass of the h¢ \eta{^\prime} boson (the ninth, would-be Goldstone boson) is decreased, thus its production cross-section is heavily enhanced. The h¢ \eta{^\prime} decays (through one of its decay channels) into five low-momentum pions. These pions will not contribute to measured Bose-Einstein
correlations, thus the production enhancement changes the strength of two-pion correlation functions at low momentum. Preliminary
results on Bose-Einstein correlation functions support the mass decrease of the h¢ \eta{^\prime} boson. In this paper we propose a method to select pions originating from h¢ \eta{^\prime} decays. We investigate the efficiency of the proposed kinematical cut in several collision systems and energies with several
simulators. We prove that our method can be used in all investigated collision systems. 相似文献
16.
Using the technique of integration within an ordered product of operators, we construct a new common eigenvector set of the complex scalar fields φ(x) and φ?(x), which is a set of particle-antiparticle correlated states. On the basis of the new eigenstates we develop the path integral formuation. The new eigenvectors' properties are investigated, they are qualified to be a new representation. 相似文献
17.
《Physics of Atomic Nuclei》2005,68(4):549-553
On the 70th Anniversary of Yurii Antonovich Simonov
70th birthday of Yuri $\overset{\lower0.5em\hbox{$\overset{\lower0.5em\hbox{ Antonovich Simonov 相似文献18.
Laser-microwave double resonance techniques applied to a cloud of a natural mixture of Eu
+ isotopes confined in a Penning trap has been used to induce and detect nuclear Zeeman transitions. In spite of the complex level structure of Eu
+ and overlapping spectra from the two isotopes five different
transitions could be observed from which the nuclear magnetic moment can be derived. We obtain for 151
Eu
+
g
I
= 1.377 34(6) demonstrating the potential for high accuracy of the technique. The experiment can be considered as a feasibility test that precise spectroscopy data using the ion storage technique can be obtained of very complex ions and under unfavourable conditions.Received: 13 June 2003, Published online: 12 August 2003PACS:
32.60. + i Zeeman and Stark effects - 32.10.Dk Electric and magnetic moments, polarizability 相似文献
19.
Journal of High Energy Physics - We construct 1/4 BPS, threshold F-Dp bound states (with 0 ≤ p ≤ 5) of type II string theories by applying S- and T-dualities to... 相似文献