314 research outputs found
Rare decay Z --> neutrino antineutrino photon photon via quartic gauge boson couplings
We present a detailed calculation of the rare decay Z --> neutrino
antineutrino photon photon via the quartic neutral gauge boson coupling
Z-Z-photon-photon in the framework of the effective Lagrangian approach. The
current experimental bound on this decay mode is then used to constrain the
coefficients of this coupling. It is found that the bounds obtained in this
way, of the order of , are weaker than the ones obtained from the
analysis of triple-boson production at LEP-2Comment: 5 pages, 2 figures, to appear in Physical Review D Brief Report
Bosonic Quartic Couplings at LHC
We analyze the potential of the CERN Large Hadron Collider (LHC) to study
anomalous quartic vector-boson interactions Z Z gamma gamma, Z Z Z gamma, W+ W-
gamma gamma, and W+ W- Z gamma through the weak boson fusion processes q q -> q
q gamma gamma and q q -> q q gamma Z(-> l+ l-) with l = electron or muon. After
a careful study of the backgrounds and how to extract them from the data, we
show that the process p p -> j j gamma l+ l- is potentially the most sensitive
to deviations from the Standard Model, improving the sensitivity to anomalous
couplings by up to a factor 10^4 (10^2) with respect to the present direct
(indirect) limits.Comment: 18 pages, 2 figures, revised versio
Vacuum structure for expanding geometry
We consider gravitational wave modes in the FRW metrics in a de Sitter phase
and show that the state space splits into many unitarily inequivalent
representations of the canonical commutation relations. Non-unitary time
evolution is described as a trajectory in the space of the representations. The
generator of time evolution is related to the entropy operator. The
thermodynamic arrow of time is shown to point in the same direction of the
cosmological arrow of time. The vacuum is a two-mode SU(1,1) squeezed state of
thermo field dynamics. The link between expanding geometry, squeezing and
thermal properties is exhibited.Comment: Latex file, epsfig, 1 figure, 21 page
Variational Approach to Gaussian Approximate Coherent States: Quantum Mechanics and Minisuperspace Field Theory
This paper has a dual purpose. One aim is to study the evolution of coherent
states in ordinary quantum mechanics. This is done by means of a Hamiltonian
approach to the evolution of the parameters that define the state. The
stability of the solutions is studied. The second aim is to apply these
techniques to the study of the stability of minisuperspace solutions in field
theory. For a theory we show, both by means of perturbation
theory and rigorously by means of theorems of the K.A.M. type, that the
homogeneous minisuperspace sector is indeed stable for positive values of the
parameters that define the field theory.Comment: 26 pages, Plain TeX, no figure
Physics at the Linear Collider
The physics at the planned colliders is discussed around three main
topics corresponding to different manifestations of symmetry breaking:
physics in the no Higgs scenario, studies of the properties of the Higgs and
precision tests of SUSY. A comparison with the LHC is made for all these cases.
The mode of the linear collider will also be reviewed.Comment: 31 pages, 12 figures. Invited talk given at the Fifth Workshop on
High Energy Physics Phenomenology, Inter-University Centre for Astronomy and
Astrophysics, Pune, India, January 12 - 26, 199
Production of the neutral toppion at the e gamma colliders
In the framework of topcolor-assisted technicolor(TC2) model, we study a
neutral toppion production process in this
paper. Our results show that the production cross section of can reach the level of several tens fb, and over
neutral toppion events can be produced in the planned linear colliders
each year. Therefore, such a toppion production process provides us a unique
chance to detect toppion events and test the TC2 model. On the other hand, the
cross section of is about one order of
magnitude larger than those of some similar processes in SM and MSSM(i.e.,
in SM and in
MSSM). So, we can easily distinguish the neutral toppion from other neutral
Higgs bosons in SM and MSSM.Comment: 12 pages, 4 figures, The paper has been accepted by Phys.Rev.
Renormalization of Poincare Transformations in Hamiltonian Semiclassical Field Theory
Semiclassical Hamiltonian field theory is investigated from the axiomatic
point of view. A notion of a semiclassical state is introduced. An "elementary"
semiclassical state is specified by a set of classical field configuration and
quantum state in this external field. "Composed" semiclassical states viewed as
formal superpositions of "elementary" states are nontrivial only if the Maslov
isotropic condition is satisfied; the inner product of "composed" semiclassical
states is degenerate. The mathematical proof of Poincare invariance of
semiclassical field theory is obtained for "elementary" and "composed"
semiclassical states. The notion of semiclassical field is introduced; its
Poincare invariance is also mathematically proved.Comment: LaTeX, 40 pages; short version of hep-th/010307
Bounds on Vector Leptoquarks
We derive bounds on vector leptoquarks coupling to the first generation,
using data from low energy experiments as well as from high energy
accelerators. Similarly to the case of scalar leptoquarks, we find that the
strongest indirect bounds arise from atomic parity violation and universality
in leptonic pi decays. These bounds are considerably stronger than the first
direct bounds of HERA, restricting vector leptoquarks that couple with
electromagnetic strength to right-handed quarks to lie above 430 GeV or 460
GeV, and leptoquarks that couple with electromagnetic strength to left-handed
quarks to lie above 1.3 TeV, 1.2 TeV and 1.5 TeV for the SU(2)_W singlet,
doublet and triplet respectively.Comment: 14 Pages (LaTeX), including 1 uufiled postscript figure.
WIS-93/119/Dec-P
Much Ado About Leptoquarks: A Comprehensive Analysis
We examine the phenomenological implications of a 200 GeV leptoquark in light
of the recent excess of events at HERA. Given the relative predictions of
events rates in e^+p versus e^-p, we demonstrate that classes of leptoquarks
may be excluded, including those contained in E_6 GUT models. It is shown that
future studies with polarized beams at HERA could reveal the chirality of the
leptoquark fermionic coupling and that given sufficient luminosity in each
e^\pm_{L,R} channel the leptoquark quantum numbers could be determined. The
implications of 200-220 GeV leptoquarks at the Tevatron are examined. While
present Tevatron data most likely excludes vector leptoquarks and leptogluons
in this mass region, it does allow for scalar leptoquarks. We find that while
leptoquarks have little influence on Drell-Yan production, further studies at
the Main Injector are possible in the single production channel. We investigate
precision electroweak measurements as well as the process e^+e^-\to q\bar q at
LEP II and find they provide no further restrictions on these leptoquark
models. We then ascertain that cross section and polarization asymmetry
measurements at the NLC provide the only direct mechanism to determine the
leptoquark's electroweak quantum numbers. The single production of leptoquarks
in \gamma e collisions by both the backscattered laser and Weisacker-Williams
techniques at the NLC is also discussed. Finally, we demonstrate that we can
obtain successful coupling constant unification in models with leptoquarks,
both with or without supersymmetry. The supersymmetric case requires the GUT
group to be larger than SU(5) such as flipped SU(5)\times U(1)_X.Comment: Corrected single production cross section at Tevatron, updated atomic
parity violation constraints, 55 page
The Boson Loop Background to H -> ZZ at Photon-photon Colliders
We have performed a complete one-loop calculation of in the Standard Model, including both gauge bosons and fermions
in the loop. We confirm the large irreducible continuum background from the
-boson loop found by Jikia. We have included the photon-photon luminosity,
and find that the continuum background of transverse boson pairs prohibits
finding a heavy Higgs with mass \gtap 350 GeV in this decay mode.Comment: 16 pages + 4 PS figures included (uuencoded), MAD/PH/77
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