13,422,225 research outputs found
Determination of the Chiral Couplings L_10 and C_87 from Semileptonic Tau Decays
Using recent precise hadronic tau-decay data on the V-A spectral function,
and general properties of QCD such as analyticity, the operator product
expansion and chiral perturbation theory, we get accurate values for the QCD
chiral order parameters L_10^r(M_rho) and C_87^r(M_rho). These two low-energy
constants appear at order p^4 and p^6, respectively, in the chiral perturbation
theory expansion of the V-A correlator. At order p^4 we obtain L_10^r(M_rho) =
-(5.22\pm 0.06)10^{-3}. Including in the analysis the two-loop (order p^6)
contributions, we get L_10^r(M_rho) = -(4.06\pm 0.39)10^{-3} and C_87^r(M_rho)
= (4.89\pm 0.19)10^{-3}GeV^{-2}. In the SU(2) chiral effective theory, the
corresponding low-energy coupling takes the value \overline l_5 = 13.30 \pm
0.11 at order p^4, and \overline l_5 = 12.24 \pm 0.21 at order p^6.Comment: 17 pages, 3 figures, v2: Added reference, published versio
Biconservative submanifolds in and
In this paper, we study biconservative submanifolds in and with parallel mean curvature
vector field and co-dimension 2. We obtain some necessary and sufficient
conditions for such submanifolds to be conservative. In particular, we obtain a
complete classification of 3-dimensional biconservative submanifolds in
and with
nonzero parallel mean curvature vector field. We also get some results for
biharmonic submanifolds in and
.Comment: 17 page
SU(3) monopoles and their fields
Some aspects of the fields of charge two SU(3) monopoles with minimal
symmetry breaking are discussed. A certain class of solutions look like SU(2)
monopoles embedded in SU(3) with a transition region or ``cloud'' surrounding
the monopoles. For large cloud size the relative moduli space metric splits as
a direct product AH\times R^4 where AH is the Atiyah-Hitchin metric for SU(2)
monopoles and R^4 has the flat metric. Thus the cloud is parametrised by R^4
which corresponds to its radius and SO(3) orientation. We solve for the
long-range fields in this region, and examine the energy density and rotational
moments of inertia. The moduli space metric for these monopoles, given by
Dancer, is also expressed in a more explicit form.Comment: 17 pages, 3 figures, latex, version appearing in Phys. Rev.
D-instantons, Strings and M-theory
The R^4 terms in the effective action for M-theory compactified on a
two-torus are motivated by combining one-loop results in type II superstring
theories with the Sl(2,Z) duality symmetry. The conjectured expression
reproduces precisely the tree-level and one-loop R^4 terms in the effective
action of the type II string theories compactified on a circle, together with
the expected infinite sum of instanton corrections. This conjecture implies
that the R^4 terms in ten-dimensional string type II theories receive no
perturbative corrections beyond one loop and there are also no non-perturbative
corrections in the ten-dimensional IIA theory. Furthermore, the
eleven-dimensional M-theory limit exists, in which there is an R^4 term that
originates entirely from the one-loop contribution in the type IIA theory and
is related by supersymmetry to the eleven-form C^{(3)}R^4. The generalization
to compactification on T^3 as well as implications for non-renormalization
theorems in D-string and D-particle interactions are briefly discussed.Comment: harvmac (b) 17 pages. v4: Some formulae corrected. Dimensions
corrected for eleven-dimensional expression
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