1,021 research outputs found
The Hidden Quantum Groups Symmetry of Super-renormalizable Gravity
In this paper we consider the relation between the super-renormalizable
theories of quantum gravity (SRQG) studied in [arXiv:1110.5249v2,
arXiv:1202.0008] and an underlying non-commutativity of spacetime. For one
particular super-renormalizable theory we show that at linear level (quadratic
in the Lagrangian) the propagator of the theory is the same we obtain starting
from a theory of gravity endowed with {\theta}-Poincar\'e quantum groups of
symmetry. Such a theory is over the so called {\theta}-Minkowski non-commuative
spacetime. We shed new light on this link and show that among the theories
considered in [arXiv:1110.5249v2, arXiv:1202.0008], there exist only one
non-local and Lorentz invariant super-renormalizable theory of quantum gravity
that can be described in terms of a quantum group symmetry structure. We also
emphasize contact with pre-existent works in the literature and discuss
preservation of the equivalence principle in our framework.Comment: 10 page
The strong coupling, unification, and recent data
The prediction of the strong coupling assuming (supersymmetric) coupling
constant unification is reexamined. We find, using the new electroweak data,
. The implications of the large
value are discussed. The role played by the beauty width is
stressed. It is also emphasized that high-energy (but not low-energy)
corrections could significantly diminish the prediction. However, unless
higher-dimension operators are assumed to be suppressed, at present one cannot
place strong constraints on the super-heavy spectrum. Non-leading electroweak
threshold corrections are also discussed.Comment: 12 pages, LaTex + RevTex, uuencoded postscript file (including 13
figures) is attached. Also available at ftp://dept.physics.upenn.edu/pub/Ni
Atomic Parity Violation and Precision Electroweak Physics - An Updated Analysis
A new analysis of parity violation in atomic cesium has led to the improved
value of the weak charge, . The implications
of this result for constraining the Peskin-Takeuchi parameters S and T and for
guiding searches for new Z bosons are discussed.Comment: 8 pages, LaTeX, 3 figures, Submitted to Physical Review D. Updated
experimental inputs and references; clarification of notatio
Electroweak radiative corrections to deep-inelastic neutrino scattering - implications for NuTeV ?
We calculate the O(alpha) electroweak corrections to charged- and
neutral-current deep-inelastic neutrino scattering off an isoscalar target. The
full one-loop-corrected cross sections, including hard photonic corrections,
are evaluated and compared to an earlier result which was used in the NuTeV
analysis. In particular, we compare results that differ in input-parameter
scheme, treatment of real photon radiation and factorization scheme. The
associated shifts in the theoretical prediction for the ratio of neutral- and
charged-current cross sections can be larger than the experimental accuracy of
the NuTeV result.Comment: 19 pages late
Chiral Symmetry Breaking and Pion Wave Function
We consider here chiral symmetry breaking through nontrivial vacuum structure
with quark antiquark condensates. We then relate the condensate function to the
wave function of pion as a Goldstone mode. This simultaneously yields the pion
also as a quark antiquark bound state as a localised zero mode in vacuum. We
illustrate the above with Nambu Jona-Lasinio model to calculate different
pionic properties in terms of the vacuum structure for breaking of exact or
approximate chiral symmetry, as well as the condensate fluctuations giving rise
to mesons.Comment: latex, revtex, 16 page
Looking for a varying in the Cosmic Microwave Background
We perform a likelihood analysis of the recently released BOOMERanG and
MAXIMA data, allowing for the possibility of a time-varying fine-structure
constant. We find that in general this data prefers a value of that
was smaller in the past (which is in agreement with measurements of
from quasar observations). However, there are some interesting degeneracies in
the problem which imply that strong statements about can not be made
using this method until independent accurate determinations of
and are available.
We also show that a preferred lower value of comes mainly from the
data points around the first Doppler peak, whereas the main effect of the
high- data points is to increase the preferred value for
(while also tightening the constraints on and ). We comment on
some implications of our results.Comment: 15 pages; submitted to Phys. Rev.
R parity violating contribution to
In this article we consider the contribution of violating couplings to
the process at high energy lepton collider.
We show that the present upper bound on the relevant violating coulpings
obtained from low energy measurements would produce a few hundred to a thousand
top-charm events at the next linear collider. Hence, it
should be possible to observe the rare process at future lepton collider.Comment: LaTEX, 13 pages, one figure is removed. A brief discussion on
possible backgrounds is added. To appear in Phys. Rev.
Rare Kaon Decay K^+ --> \pi^+ \nu \bar{\nu} in SU(3)_C X SU(3)_L X U(1)_N Models
The rare kaon decay K^+ --> \pi^+ \nu \bar{\nu} is considered in the
framework of the models based on the SU(3)_C X SU(3)_L X U(1)_N (3 - 3 - 1)
gauge group. It is shown that a lower bound of the Z' mass in the 3 - 3 - 1
model with right-handed neutrinos at a value of 3 TeV is derived, while that in
the minimal version -- 1.7 TeV.Comment: 7 pages, 1 figure, late
Standard Model Contributions to the Neutrino Index of Refraction in the Early Universe
With the standard electroweak interactions, the lowest-order coherent forward
scattering amplitudes of neutrinos in a CP symmetric medium (such as the early
universe) are zero, and the index of refraction of a propagating neutrino can
only arise from the expansion of gauge boson propagators, from radiative
corrections, and from new physics interactions. Motivated by nucleosynthesis
constraints on a possible sterile neutrino (suggested by the solar neutrino
deficit and a possible neutrino), we calculate the standard model
contributions to the neutrino index of refraction in the early universe,
focusing on the period when the temperature was of the order of a few . We
find sizable radiative corrections to the tree level result obtained by the
expansion of the gauge boson propagator. For the leading log correction is about , while for
the correction is about
. Depending on the family mixing (if any), effects from different family
scattering can be dominated by radiative corrections. The result for
is zero at one-loop level, even if neutrinos are
massive. The cancellation of infrared divergence in a coherent process is also
discussed.Comment: 46pp, 13 figures (not included), UPR-0495
On the quest for unification - simplicity and antisimplicity
The road towards unification of elementary interactions is thought to start
on the solid ground of a universal local gauge principle. I discuss the
different types of bosonic gauge symmetries in gravitational and
nongravitational (standard model) interactions and their extensions both
fermionic, bosonic and with respect to space-time dimensions. The apparently
paradoxical size and nature of the cosmological constant is sketched, which at
first sight does not readily yield a clue as to the envelopping symmetry
structure of a unified theory. Nevertheless a tentative outlook is given
encouraging to proceed on this road.Comment: 29 pages, 4 figure
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