101 research outputs found
A Comment on the Relationship Between Differential and Dimensional Renormalization
We show that there is a very simple relationship between differential and
dimensional renormalization of low-order Feynman graphs in renormalizable
massless quantum field theories. The beauty of the differential approach is
that it achieves the same finite results as dimensional renormalization without
the need to modify the space time dimension
The Hunting of the MR Model
We consider experimental signatures of the standard model's minimal
supersymmetric extension with a continuous symmetry (MR model). We
focus on the ability of existing and planned electron-positron colliders to
probe this model and to distinguish it from both the standard model and the
standard model's minimal supersymmetric extension with a discrete -parity.Comment: TeX (uses harvmac). 18 pages. Revision: added text and figure about
effects of b-jet tagging at LEP II. 7 figures available on request. CTP \#
2190. HUTP-92/A05
Leptogenesis from oscillations and dark matter
An extension of the Standard Model with Majorana singlet fermions in the
1-100 GeV range can give rise to a baryon asymmetry at freeze-in via the
CP-violating oscillations of these neutrinos: this is the well known ARS
mechanism. In this paper we consider possible extensions of the minimal ARS
scenario that can account not only for successful leptogenesis but also explain
other open problems such as dark matter. We find that an extension in the form
of a weakly coupled B-L gauge boson, an invisible QCD axion model, and the
singlet majoron model can simultaneously account for dark matter and the baryon
asymmetry.Comment: A relevant previously neglected process has been included,
conclusions mostly unchanged. Matches published versio
The Dispirited Case of Gauged Dark Matter
We explore the constraints and phenomenology of possibly the simplest
scenario that could account at the same time for the active neutrino masses and
the dark matter in the Universe within a gauged symmetry, namely
right-handed neutrino dark matter. We find that null searches from lepton and
hadron colliders require dark matter with a mass below 900 GeV to annihilate
through a resonance. Additionally, the very strong constraints from high-energy
dilepton searches fully exclude the model for . We further explore the phenomenology in the high mass region
(i.e. masses ) and highlight theoretical
arguments, related to the appearance of a Landau pole or an instability of the
scalar potential, disfavoring large portions of this parameter space.
Collectively, these considerations illustrate that a minimal extension of the
Standard Model via a local symmetry with a viable thermal dark
matter candidate is difficult to achieve without fine-tuning. We conclude by
discussing possible extensions of the model that relieve tension with collider
constraints by reducing the gauge coupling required to produce the correct
relic abundance.Comment: 21 pages, 8 figures. v2: References added. Matches the published
versio
CP Violation in the SUSY Seesaw: Leptogenesis and Low Energy
We suppose that the baryon asymmetry is produced by thermal leptogenesis
(with flavour effects), at temperatures GeV, in the
supersymmetric seesaw with universal and real soft terms. The parameter space
is restricted by assuming that processes will be
seen in upcoming experiments. We study the sensitivity of the baryon asymmetry
to the phases of the lepton mixing matrix, and find that leptogenesis can work
for any value of the phases. We also estimate the contribution to the electric
dipole moment of the electron, arising from the seesaw, and find that it is
(just) beyond the sensitivity of next generation experiments (\lsim 10^{-29}
e cm). The fourteen dimensional parameter space is efficiently explored with a
Monte Carlo Markov Chain, which concentrates on the regions of interest.Comment: 30 pages, 7 figure
Conformal Symmetry and Differential Regularization of the Three-Gluon Vertex
The conformal symmetry of the QCD Lagrangian for massless quarks is broken
both by renormalization effects and the gauge fixing procedure. Renormalized
primitive divergent amplitudes have the property that their form away from the
overall coincident point singularity is fully determined by the bare
Lagrangian, and scale dependence is restricted to -functions at the
singularity. If gauge fixing could be ignored, one would expect these
amplitudes to be conformal invariant for non-coincident points. We find that
the one-loop three-gluon vertex function is
conformal invariant in this sense, if calculated in the background field
formalism using the Feynman gauge for internal gluons. It is not yet clear why
the expected breaking due to gauge fixing is absent. The conformal property
implies that the gluon, ghost and quark loop contributions to
are each purely numerical combinations of two universal
conformal tensors and whose
explicit form is given in the text. Only has an ultraviolet
divergence, although requires a careful definition to resolve
the expected ambiguity of a formally linearly divergent quantity.
Regularization is straightforward and leads to a renormalized vertex function
which satisfies the required Ward identity, and from which the beta-function is
easily obtained. Exact conformal invariance is broken in higher-loop orders,
but we outline a speculative scenario in which the perturbative structure of
the vertex function is determined from a conformal invariant primitive core by
interplay of the renormalization group equation and Ward identities.Comment: 65 page
- …