829 research outputs found
Large N_c
The 1/N_c expansion of QCD with N_c=3 has been successful in explaining a
wide variety of QCD phenomenology. Here I focus on the contracted spin-flavor
symmetry of baryons in the large-N_c limit and deviations from spin-flavor
symmetry due to corrections suppressed by powers of 1/N_c. Baryon masses
provide an important example of the 1/N_c expansion, and successful predictions
of masses of heavy-quark baryons continue to be tested by experiment. The
ground state charmed baryon masses have all been measured, and five of the
eight ground state bottom baryon masses have been found. Results of the 1/N_c
expansion can aid in the discovery of the remaining bottom baryons. The brand
new measurement of the \Omega_b^- mass by the CDF collaboration conflicts with
the original D0 discovery value and is in excellent agreement with the
prediction of the 1/N_c expansion.Comment: 4 pages, Invited talk at CIPANP 2009, May 26-31, 2009, to be
published in the proceeding
Algebraic Structure of Lepton and Quark Flavor Invariants and CP Violation
Lepton and quark flavor invariants are studied, both in the Standard Model
with a dimension five Majorana neutrino mass operator, and in the seesaw model.
The ring of invariants in the lepton sector is highly non-trivial, with
non-linear relations among the basic invariants. The invariants are classified
for the Standard Model with two and three generations, and for the seesaw model
with two generations, and the Hilbert series is computed. The seesaw model with
three generations proved computationally too difficult for a complete solution.
We give an invariant definition of the CP-violating angle theta in the
electroweak sector
Naturalness of the Coleman-Glashow Mass Relation in the 1/N_c Expansion: an Update
A new measurement of the Xi^0 mass verifies the accuracy of the
Coleman-Glashow relation at the level predicted by the 1/N_c expansion. Values
for other baryon isospin mass splittings are updated, and continue to agree
with the 1/N_c hierarchy.Comment: 6 pages, revte
Low-Energy Effective Field Theory below the Electroweak Scale: Operators and Matching
The gauge-invariant operators up to dimension six in the low-energy effective
field theory below the electroweak scale are classified. There are 70 Hermitian
dimension-five and 3631 Hermitian dimension-six operators that conserve baryon
and lepton number, as well as , , and operators. The matching onto these operators from the
Standard Model Effective Field Theory (SMEFT) up to order is
computed at tree level. SMEFT imposes constraints on the coefficients of the
low-energy effective theory, which can be checked experimentally to determine
whether the electroweak gauge symmetry is broken by a single fundamental scalar
doublet as in SMEFT. Our results, when combined with the one-loop anomalous
dimensions of the low-energy theory and the one-loop anomalous dimensions of
SMEFT, allow one to compute the low-energy implications of new physics to
leading-log accuracy, and combine them consistently with high-energy LHC
constraints.Comment: 44 pages, 22 tables; version published in JHE
On Gauge Invariance and Minimal Coupling
The principle of minimal coupling has been used in the study of Higgs boson
interactions to argue that certain higher dimensional operators in the
low-energy effective theory generalization of the Standard Model are suppressed
by loop factors, and thus smaller than others. It also has been extensively
used to analyze beyond-the-standard-model theories. We show that in field
theory, and even in quantum mechanics, the concept of minimal coupling is
ill-defined and inapplicable as a general principle, and give many pedagogical
examples which illustrate this fact. We also clarify some related
misconceptions about the dynamics of strongly coupled gauge theories. Many
arguments in the literature on Higgs boson interactions that use minimal
coupling, particularly in pseudo-Goldstone Higgs theories, are inherently
flawed.Comment: 25 pp, 2 figures v2: refs added, JHEP version, conclusions unchange
Renormalization Group Scaling of Higgs Operators and \Gamma(h -> \gamma \gamma)
We compute the renormalization of dimension six Higgs-gauge boson operators
that can modify \Gamma(h -> \gamma \gamma) at tree-level. Operator mixing is
shown to lead to an important modification of new physics effects which has
been neglected in past calculations. We also find that the usual formula for
the S oblique parameter contribution of these Higgs-gauge boson operators needs
additional terms to be consistent with renormalization group evolution. We
study the implications of our results for Higgs phenomenology and for new
physics models which attempt to explain a deviation in \Gamma(h -> \gamma
\gamma). We derive a new relation between the S parameter and the \Gamma(h ->
\gamma \gamma) and \Gamma(h ->Z \gamma) decay rates.Comment: 20 pp. 2 fi
Non-Perturbative Effects in
We compute the non-perturbative contribution of semileptonic tensor operators
to the purely
leptonic process and to the electric and magnetic dipole
moments of charged leptons by matching onto chiral perturbation theory at low
energies. This matching procedure has been used extensively to study
semileptonic and leptonic weak decays of hadrons. In this paper, we apply it to
observables that contain no strongly interacting external particles. The
non-perturbative contribution to processes is used to extract the
best current bound on lepton-flavor-violating semileptonic tensor operators,
TeV. We briefly discuss how the same method
applies to dark-matter interactions.Comment: 21 pages, 1 figure; version published in JHE
Higher-Order Gravitational Lensing Reconstruction using Feynman Diagrams
We develop a method for calculating the correlation structure of the Cosmic
Microwave Background (CMB) using Feynman diagrams, when the CMB has been
modified by gravitational lensing, Faraday rotation, patchy reionization, or
other distorting effects. This method is used to calculate the bias of the
Hu-Okamoto quadratic estimator in reconstructing the lensing power spectrum up
to O(\phi^4) in the lensing potential . We consider both the diagonal
noise TTTT, EBEB, etc. and, for the first time, the off-diagonal noise TTTE,
TBEB, etc. The previously noted large O(\phi^4) term in the second order noise
is identified to come from a particular class of diagrams. It can be
significantly reduced by a reorganization of the expansion. These
improved estimators have almost no bias for the off-diagonal case involving
only one component of the CMB, such as EEEB.Comment: 17 pages, 17 figure
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