106 research outputs found
Prospective Analysis Spin- and CP-sensitive Variables in H -> ZZ -> l_1 l_1 l_2 l_2 with Atlas
A possibility to prove spin and CP-eigenvalue of a Standard Model (SM) Higgs
boson is presented. We exploit angular correlations in the subsequent decay H
-> ZZ -> 4l (muons or electrons) for Higgs masses above 200 GeV. We compare the
angular distributions of the leptons originating from the SM Higgs with those
resulting from decays of hypothetical particles with differing quantum numbers.
We restrict our analysis to the use of the Atlas-detector which is one of two
multi-purpose detectors at the upcoming 14 TeV proton-proton-collider (LHC) at
CERN. By applying a fast simulation of the Atlas detector it can be shown that
these correlations will be measured sufficiently well that consistency with the
spin-CP hypothesis 0+ of the Standard Model can be verified and the 0- and 1+-
can be ruled out with an integrated luminosity of 100 fb^-1.Comment: 25 pages, 9 figures Version 2: Minor changes made as requested by
Atlas referee and Springer editor. Added a chapter where background
subtraction is detaile
Collider Tests of Compact Space Dimensions Using Weak Gauge Bosons
We present collider tests of the recent proposal for weak-scale quantum
gravity due to new large compact space dimensions in which only the graviton
(\G) propagates. We show that the existing high precision LEP-I -pole data
can impose non-trivial constraints on the scale of the new dimensions, via the
decay mode Z\to f\bar{f}+\G (). These bounds are comparable to
those obtained at high energy colliders and provide the first sensitive probe
of the scalar graviton. We also study W(Z)+\G production and the anomalous
signal from virtual \G-states at the Fermilab Tevatron, and compare
them with the LEP-I bound and those from LEP-II and future linear colliders.Comment: 4 pages, 1 postscript figure include
Photons, neutrinos and large compact space dimensions
We compute the contribution of Kaluza-Klein graviton exchange to the cross
section for photon-neutrino scattering. Unlike the usual situation where the
virtual graviton exchange represents a small correction to a leading order
electroweak or strong amplitude, in this case the graviton contribution is of
the same order as the electroweak amplitude, or somewhat larger. Inclusion of
the graviton contribution is not sufficient to allow high energy neutrinos to
scatter from relic neutrinos in processes such as
, but the photon-neutrino decoupling temperature
is substantially reduced.Comment: 8 pages, 3 figures LaTeX. Typos correcte
Photons, neutrinos and optical activity
We compute the one-loop helicity amplitudes for low-energy
scattering and its crossed channels in the standard
model with massless neutrinos. In the center of mass, with , the cross sections for these channels grow roughly
as . The scattered photons in the elastic channel are circularly
polarized and the net value of the polarization is non-zero. We also present a
discussion of the optical activity of a sea of neutrinos and estimate the
values of its index of refraction and rotary power.Comment: 9 pages, ReVTeX4, 6 figures include
Charges on Strange Quark Nuggets in Space
Since Witten's seminal 1984 paper on the subject, searches for evidence of
strange quark nuggets (SQNs) have proven unsuccessful. In the absence of
experimental evidence ruling out SQNs, the validity of theories introducing
mechanisms that increase their stability should continue to be tested. To
stimulate electromagnetic SQN searches, particularly space searches, we
estimate the net charge that would develop on an SQN in space exposed to
various radiation baths (and showers) capable of liberating their less strongly
bound electrons, taking into account recombination with ambient electrons. We
consider, in particular, the cosmic background radiation, radiation from the
sun, and diffuse galactic and extragalactic -ray backgrounds. A
possible dramatic signal of SQNs in explosive astrophysical events is noted.Comment: CitationS added, new subsection added, more discussion, same
numerical result
gamma nu -> gamma gamma nu and crossed processes at energies below m_W
The cross sections for the processes ,
and are
calculated for a range of center of mass energies from below to
considerably above , but much less than . This enables us to treat
the neutrino--electron coupling as a four--Fermi interaction and results in
amplitudes which are electron box diagrams with three real photons and one
virtual photon at their vertices. These calculations extend our previous
low--energy effective interaction results to higher energies and enable us to
determine where the effective theory is reliable.Comment: 12 pages, RevTex, 10 postscript figures include
Effective Lagrangians and low energy photon-photon scattering
We use the behavior of the photon-photon scattering for photon energies
less than the electron mass, , to examine the implications of
treating the Euler-Heisenberg Lagrangian as an effective field theory.
Specifically, we determine the behavior of the scattering
amplitude predicted by including one-loop corrections to the Euler-Heisenberg
effective Lagrangian together with the counterterms required by
renomalizability. This behavior is compared with the energy dependence obtained
by expanding the exact QED photon-photon scattering amplitude. If the
introduction of counterterms in the effective field theory is restricted to
those determined by renormalizability, the dependences of the
two expansions differ.Comment: 10 pages, ReVTeX, 2 postscript figures include
W, Z and Higgs Scattering at SSC Energies
We examine the scattering of longitudinal , and Higgs bosons in the
Standard Model using the equivalent Goldstone-boson Lagrangian. Our
calculations include the full one-loop scattering matrix between the states
, and with no restrictions on the relative sizes of
and . In addition to deriving the perturbative
eigen-amplitudes, we also obtain quite striking results by unitarizing the
amplitudes with the use of the K-matrix and Pad\'e techniques. (Complete
postscript file can be obtained by anonymous ftp from hal.physics.wayne.edu as
dpf92g.ps in directory pub/physics )Comment: Talk presented at DPF92, November 10-14, 1992. 3 pages with 6
PostScript figures included. LaTeX fil
Cosmological constraints combining H(z), CMB shift and SNIa observational data
Recently H(z) data obtained from differential ages of galaxies have been
proposed as a new geometrical probe of dark energy. In this paper we use those
data, combined with other background tests (CMB shift and SNIa data), to
constrain a set of general relativistic dark energy models together with some
other models motivated by extra dimensions. Our analysis rests mostly on
Bayesian statistics, and we conclude that LCDM is at least substantially
favoured, and that braneworld models are less favoured than general
relativistic ones.Comment: 17 pages, 11 figures; improved discussion, new figures, updated to
match published versio
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