19 research outputs found
Realistic Anomaly-mediated Supersymmetry Breaking
We consider supersymmetry breaking communicated entirely by the
superconformal anomaly in supergravity. This scenario is naturally realized if
supersymmetry is broken in a hidden sector whose couplings to the observable
sector are suppressed by more than powers of the Planck scale, as occurs if
supersymmetry is broken in a parallel universe living in extra dimensions. This
scenario is extremely predictive: soft supersymmetry breaking couplings are
completely determined by anomalous dimensions in the effective theory at the
weak scale. Gaugino and scalar masses are naturally of the same order, and
flavor-changing neutral currents are automatically suppressed. The most glaring
problem with this scenario is that slepton masses are negative in the minimal
supersymmetric standard model. We point out that this problem can be simply
solved by coupling extra Higgs doublets to the leptons. Lepton flavor-changing
neutral currents can be naturally avoided by approximate symmetries. We also
describe more speculative solutions involving compositeness near the weak
scale. We then turn to electroweak symmetry breaking. Adding an explicit \mu
term gives a value for B\mu that is too large by a factor of order 100. We
construct a realistic model in which the \mu term arises from the vacuum
expectation value of a singlet field, so all weak-scale masses are directly
related to m_{3/2}. We show that fully realistic electroweak symmetry breaking
can occur in this model with moderate fine-tuning.Comment: 32 pages, LaTeX2e, 3 eps figure
NEW PHYSICS AND RECENT HIGH PRECISION ELECTROWEAK MEASUREMENTS
We analyze LEP and SLC data from the 1995 Winter Conferences for signals of
new physics. We compare the data with the Standard Model (SM) as well as a
number of test hypotheses concerning the nature of new physics: (i) nonstandard
Zbb couplings, (ii) nonstandard Zff couplings for the entire third generation,
(iii) nonstandard oblique corrections, (iv) nonstandard lepton couplings, (v)
general nonstandard W and Z couplings to all fermions, as well as combinations
of the above. In most of our analyses, we leave the SM variables and
as free parameters to see how the various types of new physics can affect
their inferred values. We find that the best fit () is
obtained for the nonstandard Zbb couplings, which also give a `low' value
(0.112) for . The SM also gives a good description of the Z data,
having . If is held fixed to the low-energy
value 0.112, then we find that a combination of the nonstandard Zbb couplings
is fit to lie more than four standard deviations away from zero.Comment: Plain TeX, 9 pages, one figure (uuencoded), and 8 table
Hadronic production calculated in the NRQCD factorization formalism
The NRQCD factorization formalism of Bodwin, Braaten, and Lepage prescribes
how to write quarkonium production rates as a sum of products of short-distance
coefficients times non-perturbative long-distance NRQCD matrix elements. We
present, in the true spirit of the factorization formalism, a detailed
calculation of the inclusive cross section for hadronic production. We
find that in addition to the well known {\it color-singlet} production
mechanisms, there are equally important mechanisms in which the pair
that forms the is initially produced in a {\it color-octet} state, in
either a , , or angular-momentum
configuration. In our presentation, we emphasize the ``matching'' procedure,
which %is the method that allows us to determine the short-distance
coefficients appearing in the factorization formula. We also point out how one
may systematically include relativistic corrections in these calculations.Comment: 25 pages, 3 postscript figures, use Revtex and epsfig.sty We fixed
some typos, added some text regarding a reference, and changed some
equations. The file will be available at http://phenom.physics.wisc.edu
A Global Fit to Extended Oblique Parameters
The STU formalism of Peskin and Takeuchi is an elegant method for encoding
the measurable effects of new physics which couples to light fermions
dominantly through its effects on electroweak boson propagation. However, this
formalism cannot handle the case where the scale of new physics is not much
larger than the weak scale. In this case three new parameters (V, W and X) are
required. We perform a global fit to precision electroweak data for these six
parameters. Our results differ from what is found for just STU. In particular
we find that the preference for S < 0 is not maintained.Comment: Plain TeX, 11 pages, one figure (ps file enclosed), (replaced version
corrects minor TeX problem, text unchanged) UdeM-LPN-TH-93-166, McGill-93/24,
OCIP/C-93-
NRQCD matrix elements in polarization of J-Psi produced from b-decay
We present the non-relativistic QCD (NRQCD) prediction for the polarization
of the J-Psi produced in b to J-Psi + X, as well as the helicity-summed
production rate. We propose that these observables provide a means of measuring
the three most important color-octet NRQCD matrix elements involved in J-Psi
production. Anticipating the measurement of the polarization parameter alpha,
we determine its expected range given current experimental bounds on the
color-octet matrix elements.Comment: 9 pages, Revtex, 2 figure
Bounding Anomalous Gauge-Boson Couplings
In this version we have corrected some minor errors in the tables, corrected
typos, and added a reference. We have also updated our comparison with earlier
workers. Figures are now included as uuencoded compressed tar files.Comment: 32 page
Model-Independent Global Constraints on New Physics
Using effective-lagrangian techniques we perform a systematic survey of the
lowest-dimension effective interactions through which heavy physics might
manifest itself in present experiments. We do not restrict ourselves to special
classes of effective interactions (such as `oblique' corrections). We compute
the effects of these operators on all currently well-measured electroweak
observables, both at low energies and at the resonance, and perform a
global fit to their coefficients. Despite the fact that a great many operators
arise in our survey, we find that most are quite strongly bounded by the
current data. We use our survey to systematically identify those effective
interactions which are {\it not} well-bounded by the data -- these could very
well include large new-physics contributions. Our results may also be used to
efficiently confront specific models for new physics with the data, as we
illustrate with an example.Comment: plain TeX, 68 pages, 2 figures (postscript files appended),
McGill-93/12, NEIPH-93-008, OCIP/C-93-6, UQAM-PHE-93/08, UdeM-LPN-TH-93-15
Photoproduction of J/ in the forward region
We study the phenomenology of fixed-target elastic photoproduction
in the NRQCD factorization formalism. Our the goal is to test an essential
feature of this formalism --- the color-octet mechanism. We obtain an
order-of-magnitude estimate for a certain linear combination of NRQCD
color-octet matrix elements. Our estimate is consistent with other empirical
determinations and with the -scaling rules of NRQCD.Comment: Version to appear in Phys. Rev. Substantial change