61,996 research outputs found
Massless Monopoles and Multipronged Strings
We investigate the role of massless magnetic monopoles in the N=4
supersymmetric Yang-Mills Higgs theories. They can appear naturally in the
1/4-BPS dyonic configurations associated with multi-pronged string
configurations. Massless magnetic monopoles can carry nonabelian electric
charge when their associated gauge symmetry is unbroken. Surprisingly, massless
monopoles can also appear even when the gauge symmetry is broken to abelian
subgroups.Comment: 10 pages, LaTex file, more comments added. (To appear in Phys. Lett.
B
Entropy Production during Asymptotically Safe Inflation
The Asymptotic Safety scenario predicts that the deep ultraviolet of Quantum
Einstein Gravity is governed by a nontrivial renormalization group fixed point.
Analyzing its implications for cosmology using renormalization group improved
Einstein equations we find that it can give rise to a phase of inflationary
expansion in the early Universe. Inflation is a pure quantum effect here and
requires no inflaton field. It is driven by the cosmological constant and ends
automatically when the renormalization group evolution has reduced the vacuum
energy to the level of the matter energy density. The quantum gravity effects
also provide a natural mechanism for the generation of entropy. It could easily
account for the entire entropy of the present Universe in the massless sector.Comment: 17 pages, 4 figures, Invited contribution to the special issue of
Entropy on "Entropy in Quantum Gravity
Nucleon-Nucleon Scattering and Effective Field Theory: Including Pions Non-perturbatively
Next to leading order effective field theory calculations are performed for NN scattering using subtractive renormalization procedure. One pion
exchange and contact interaction potentials are iterated using
Lippman-Schwinger equation. Satisfactory fit to the Nijmegen data is obtained
for the momenta up to 300 MeV in the centre of mass frame. Phase shifts are
also compared with the results of KSW approach where pions are included
perturbatively.Comment: 7 pages, 3 figures, references added, to appear in Phys. Lett.
Six-dimensional Methods for Four-dimensional Conformal Field Theories
The calculation of both spinor and tensor Green's functions in
four-dimensional conformally invariant field theories can be greatly simplified
by six-dimensional methods. For this purpose, four-dimensional fields are
constructed as projections of fields on the hypercone in six-dimensional
projective space, satisfying certain transversality conditions. In this way
some Green's functions in conformal field theories are shown to have structures
more general than those commonly found by use of the inversion operator. These
methods fit in well with the assumption of AdS/CFT duality. In particular, it
is transparent that if fields on AdS approach finite limits on the boundary
of AdS, then in the conformal field theory on this boundary these limits
transform with conformal dimensionality zero if they are tensors (of any rank),
but with conformal dimension 1/2 if they are spinors or spinor-tensors.Comment: Version accepted for publication in Physical Review D. References to
earlier work added in footnote 2. Minor errors corrected. 24 page
Dark Energy and the Nature of the Graviton
Does the existence of dark energy suggest that there is more to the graviton
than we think we know?Comment: 4 page
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