553,350 research outputs found
Free energy and theta dependence of SU(N) gauge theories
We study the dependence of the free energy on the CP violating angle theta,
in four-dimensional SU(N) gauge theories with N >= 3, and in the large-N limit.
Using the Wilson lattice formulation for numerical simulations, we compute
the first few terms of the expansion of the ground-state energy F(theta) around
theta = 0, F(theta) - F(0) = A_2 theta^2 (1 + b_2 theta^2 + ...). Our results
support Witten's conjecture: F(theta) - F(0) = A theta^2 + O(1/N) for theta <
pi.
We verify that the topological susceptibility has a nonzero large-N limit
chi_infinity = 2A with corrections of O(1/N^2), in substantial agreement with
the Witten-Veneziano formula which relates chi_infinity to the eta' mass.
Furthermore, higher order terms in theta are suppressed; in particular, the
O(theta^4) term b_2 (related to the eta' - eta' elastic scattering amplitude)
turns out to be quite small: b_2 = -0.023(7) for N=3, and its absolute value
decreases with increasing N, consistently with the expectation b_2 = O(1/N^2).Comment: 3 pages, talk presented at the conference Lattice2002(topology). v2:
One reference has been updated, no further change
Reconstruction of the Extended Gauge Structure from Observables at Future Colliders
The discovery of a new neutral gauge boson with a mass in the TeV region
would allow for determination of gauge couplings of the to ordinary quarks
and leptons in a model independent way. We show that these couplings in turn
would allow us to determine the nature of the extended gauge structure. As a
prime example we study the group. In this case two discrete constraints
on experimentally determined couplings have to be satisfied. If so, the
couplings would then uniquely determine the two parameters, and
, which fully specify the nature of the within . If the
is part of the gauge structure, then for TeV and
could be determined to around at the future colliders. The NLC
provides a unique determination of the two constraints as well as of and , though with slightly larger error bars than at the LHC. On
the other hand, since the LHC primarily determines three out of four normalized
couplings, it provides weaker constraints for the underlying gauge structure.Comment: 14 pages LaTeX using RevTeX and psfig.sty. TeX source and 3 PS
figures, tarred, compressed and uuencoded; also available via anonymous ftp
to ftp://dept.physics.upenn.edu/pub/Cvetic/UPR-636-T
Discrete regularisation of localised kinetic terms
We investigate the behaviour of 5d models with general brane kinetic terms by
discretising the extra dimension. We show that in the continuum limit the
Kaluza-Klein masses and wave functions are in general nonanalytic in the
coefficients of brane terms.Comment: Presented at the 7th DESY Workshop on Elementary Particle Theory
``Loops and Legs in Quantum Field Theory'', Zinnowitz, April 25-30, 200
Non Singular Origin of the Universe and the Cosmological Constant Problem (CCP)
We consider a non singular origin for the Universe starting from an Einstein
static Universe in the framework of a theory which uses two volume elements
and , where is a metric independent
density, also curvature, curvature square terms, first order formalism and for
scale invariance a dilaton field are considered in the action. In the
Einstein frame we also add a cosmological term that parametrizes the zero point
fluctuations. The resulting effective potential for the dilaton contains two
flat regions, for relevant for the non singular
origin of the Universe and , describing our present
Universe. Surprisingly, avoidance of singularities and stability as imply a positive but small vacuum energy as . Zero vacuum energy density for the present universe is
the "threshold" for universe creation.Comment: awarded an honorable mention in the Gravity Research Foundation 2011
Awards for Essays in Gravitation for 201
Electroweak constraints on new physics
We briefly review the limits on new interactions implied by electroweak
precision data. Special attention is payed to the bounds on the Higgs boson
mass. We also comment on the required cancellation among the new contributions
to precisely measured electroweak observables in any Standard Model extension,
if the new particles have to evade the indirect constraints on their couplings
and masses but still remain at the LHC reach.Comment: Latex 4 pages, 1 table, 2 figures. To appear in the proceedings of
10th Hellenic School and Workshops on Elementary Particle Physics and Gravity
(Corfu 2010), Corfu, Greece, Aug 29 - Sep 19, 201
The Jackiw-Pi model and its symmetries
The non-Abelian gauge model proposed by Jackiw and Pi, which generates an
even-parity mass term in three space-time dimensions, is revisited in this
letter. All the symmetries of the model are collected and established by means
of BRS invariance and Slavnov-Taylor identity. The path for the perturbatively
quantization of the Jackiw-Pi model, through the algebraic method of
renormalization, is presented.Comment: 5 page
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