摘要:

We examine the evolution of a 3-brane that separates two regions of a4+1dimensional bulk space-time with potentially different cosmological constants. We have included a term in the brane action for the scalar curvature. When one or both of the regions has a zero cosmological constant, we find solutions for which the cosmology on the brane has the same time-dependence as a standard radiation-dominated universe, but which depends on a mass parameter in the bulk metric rather than the radiation density on the brane. When a non-zero cosmological constant is present in both bulk regions, it is possible to obtain a standard Robertson-Walker evolution. We then extract the effective theory of gravity in the weak-field limit seen by an observer on the brane in each of these scenarios. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1328897

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We find all possible static embeddings of a 4-brane in any dimension-6 spacetime with 4-dimensional Poincare´ symmetry and a negative cosmological constant, subject to orbifolding across the brane. Our new solutions allow intersecting branes at an angle determined by a new dynamical parameter. A collection of branes intersecting in one 3-brane allows an arbitrary excess angle that can be related to a vacuum density along the intersection. The 3-brane must be stabilized by additional fine-tuned interactions. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1328898

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We study the geometry of a two-sheeted space-time within the framework of non-commutative geometry. As a prelude to the Standard Model in curved space-time, we present a model of a left- and a right- chiral field living on the two sheeted-space time and construct the action functionals that describe their interactions. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1328899

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We present precise predictions for the processese+e−→WW→4f(&ggr;)at LEP2 and future Linear-Collider (LC) energies obtained with the Monte Carlo generator RACOONWW. The program RACOONWW includes the completeO(&agr;)electroweak radiative corrections toe+e−→WW→4fin the double-pole approximation (DPA). While the virtual corrections are treated in DPA, the calculation of the bremsstrahlung corrections is based on the full lowest-order matrix elements to the processese+e−→4f+&ggr;.This asymmetric treatment of virtual and real photons requires a careful matching of the arising infrared and collinear singularities. We also take into account higher-order initial-state photon radiation via the structure-function method. Here, we briefly describe the RACOONWW approach, give numerical results for the total W-pair production cross sections, confront them with LEP2 data, and study the impact of the radiative corrections on angular and W-invariant-mass distributions at LEP2 and LC energies. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1328900

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Utilizing asymptotic Pade´-approximant methods, we estimate the three-loop orderMScoefficients of&agr;s3[log(&mgr;2/mb2(&mgr;))]kterms[k={0,1,2,3}]within theb→ul−&ngr;¯ldecay rate. Except for the coefficient of thek=0term, all other coefficients may also be obtained via renormalization -group (RG) methods. The relative errors in asymptotic Pade´-approximant estimates of thek={1,2,3}terms are found to be 5.1&percent; or less, thereby providing an estimate of the theoretical uncertainty in the asymptotic Pade´-approximant estimate of theRG-inaccessiblek=0term. By a judicious choice in the renormalization scale parameter, we are able to extract|Vub|from the inclusive decay rate to within ±7&percent; theoretical uncertainty. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1328901

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We discuss theO(&agr;)electroweak radiative corrections toWandZboson production and their impact on the measurement of theWmass at hadron colliders. The results of recent improved calculations are presented. We also briefly discuss theO(&agr;)corrections to Drell-Yan production in the high invariant mass region. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1328902

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We study power corrections up toO(1/mb3)to the inclusive rareBdecayB¯→Xsl+l−.The values of matrix elements entering at this order are unknown, and introduce uncertainties into physical quantities such as the dilepton invariant mass differential spectrum. Imposing a phase space cut to eliminatecc¯resonances, we find that there are two accessible phase space regions: the low invariant mass region where power corrections are small, and the high invariant mass region where the power corrections are atO(10&percent;),comparable to the perturbative uncertainties. We comment on a connection betweenB¯→Xsl+l−and|Vub|.©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1328903

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In this talk, a brief review of the &pgr;&eegr; scattering of ref. [1] is presented. Due to the importance of the &pgr;&eegr; scattering in probing light scalar mesons, the scalar meson nonet formulation of the Lagrangian developed in refs. [2,3] is first briefly reviewed. Then the result of the elastic and inelastic scattering amplitudes are displayed, and the role of scalars as well as the consistency of the framework are discussed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1328904

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Using asymptotic Pade´ approximant methods, we have calculated theO(&agr;s5)contribution to the Standard-ModelH→ggdecay rate. This process is of particular interest because of the slow convergence evident from the known terms of its QCD series. TheO(&agr;s5)term is expressed as a 3rd degree polynomial inL≡ln(&mgr;2/mt2(&mgr;)).We find that the asymptotic Pade´ predictions for the renormalization-group accessible coefficients ofL,L2andL3are within 1&percent;, 2&percent; and 7&percent; of their respective values. The inclusion of theO(&agr;s5)contribution renders the full decay rate virtually scale independent over the entire0.3MH⩽&mgr;⩽Mtrange of the renormalization scale &mgr;. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1328905

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Recent work suggests the existence of a non-conventional lowest-lying scalar nonet containing thea0(980).Then thea0(1450)and also theK0*(1430)are likely candidates to belong to a conventional p-waveqq¯nonet. However a comparison of their properties with those expected on this basis reveals a number of puzzling features. It is pointed out that these puzzles can be resolved in a natural and robust way by assuming a “bare” conventional p-wave scalarqq¯nonet to mix with a lighter four quarkqqq¯q¯scalar nonet to form new “physical” states. The essential mechanism is driven by the fact that the isospinor is lighter than the isovector in the unmixedqqq¯q¯multiplet. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1328906

出版商:AIP    

年代:1900

数据来源: AIP