12,716 research outputs found
Rigorous QCD Predictions for Decays of P-Wave Quarkonia
Rigorous QCD predictions for decay rates of the P-wave states of heavy
quarkonia are presented. They are based on a new factorization theorem which is
valid to leading order in the heavy quark velocity and to all orders in the
running coupling constant of QCD. The decay rates for all four P states into
light hadronic or electromagnetic final states are expressed in terms of two
phenomenological parameters, whose coefficients are perturbatively calculable.
Logarithms of the binding energy encountered in previous perturbative
calculations of P-wave decays are factored into a phenomenological parameter
that is related to the probability for the heavy quark-antiquark pair to be in
a color-octet S-wave state. Applying these predictions to charmonium, we use
measured decay rates for the \chione and \chitwo to predict the decay rates
of the \chizero and .Comment: 13 page
Breaking the electroweak symmetry and supersymmetry by a compact extra dimension
We revisit in some more detail a recent specific proposal for the breaking of
the electroweak symmetry and of supersymmetry by a compact extra dimension.
Possible mass terms for the Higgs and the matter hypermultiplets are considered
and their effects on the spectrum analyzed. Previous conclusions are reinforced
and put on firmer ground.Comment: 25 pages, LaTeX, 9 eps figure
Electroweak Precision Tests: A Concise Review
1. Introduction 2. Status of the Data 3. Precision Electroweak Data and the
Standard Model 4. A More General Analysis of Electroweak Data
4.1 Basic Definitions and Results
4.2 Experimental Determination of the Epsilon Variables
4.3 Comparing the Data with the Minimal Supersymmetric Standard Model 5.
Theoretical Limits on the Higgs Mass 6. ConclusionComment: Submitted to Int. Journal of Modern Physics
Vacuum oscillations of quasi degenerate solar neutrinos
The atmospheric neutrino oscillations and the vacuum oscillation solution of
the solar neutrino problem can be consistently described by a doubly or triply
degenerate neutrino spectrum as long as the high level of degeneracy required
is not spoiled by radiative corrections. We show that this is the case for
neutrino mass matrices generated by symmetries. This imposes a strong
constraint on the mixing angles and requires the mixing should be close to
bi-maximal. We briefly discuss the relevance of our results for the
measurability of the neutrino spectrum.Comment: 6 pages. Final version, more clear presentatio
Cancellation of Infrared Divergences in Hadronic Annihilation Decays of Heavy Quarkonia
In the framework of a newly developed factorization formalism which is based
on NRQCD, explicit cancellations are shown for the infrared divergences that
appeared in the previously calculated hadronic annihilation decay rates of
P-wave and D-wave heavy quarkonia. We extend them to a more general case that
to leading order in and next-to-leading order in , the infrared
divergences in the annihilation amplitudes of color-singlet
pair can be removed by including the contributions of
color-octet operators ,
, ... in NRQCD. We also give the decay widths of
at leading order in .Comment: 8 pages, LaTex(3 figures included), to be publishe
Less Minimal Flavour Violation
We consider the approximate U(2)^3 flavour symmetry exhibited by the quark
sector of the Standard Model and all its possible breaking terms appearing in
the quark Yukawa couplings. Taking an Effective Field Theory point of view, we
determine the current bounds on these parameters, assumed to control the
breaking of flavour in a generic extension of the Standard Model at a reference
scale Lambda. In particular, a significant bound from epsilon'/epsilon is
derived, which is relevant to Minimal Flavour Violation as well. In the
up-quark sector, the recently observed CP violation in D -> pi+ pi-, K+ K-
decays might be accounted for in this generic framework, consistently with any
other constraint.Comment: 15 pages, 1 figur
QCD Radiative Corrections to the Leptonic Decay Rate of the B_c Meson
The QCD radiative corrections to the leptonic decay rate of the meson
are calculated using the formalism of nonrelativistic QCD (NRQCD) to separate
short-distance and long-distance effects. The decay constant is factored
into a sum of NRQCD matrix elements each multiplied by a short-distance
coefficient. The short-distance coefficient for the leading matrix element is
calculated to order by matching a perturbative calculation in full
QCD with the corresponding perturbative calculation in NRQCD. This
short-distance correction decreases the leptonic decay rate by approximately
.Comment: Changed Eq. 2 to read 1/(8 \pi), put in a missing i M_{B_c} in Eq.
18, and put in a normalisation factor of 2 M_{B_c} in Eq. 19
Minimal Flavour Violation with hierarchical squark masses
In a supersymmetric model with hierarchical squark masses we analyze a
pattern of flavour symmetry breaking centered on the special role of the top
Yukawa coupling and, by extension, of the full Yukawa couplings for the up-type
quarks. For sufficiently heavy squarks of the first and second generation this
leads to effective Minimal Flavour Violation of the Flavour Changing Neutral
Current amplitudes. For this to happen we determine the bounds on the masses of
the heavy squarks with QCD corrections taken into account, properly including
previously neglected effects. We believe that the view presented in this paper
altogether strengthens the case for hierarchical sfermions.Comment: 13 pages, 1 figure. v2: an equation correcte
- …