39 research outputs found
Supersymmetric Large Extra Dimensions and the Cosmological Constant Problem
This article briefly summarizes and reviews the motivations for - and the
present status of - the proposal that the small size of the observed Dark
Energy density can be understood in terms of the dynamical relaxation of two
large extra dimensions within a supersymmetric higher-dimensional theory.Comment: Talk presented to Theory Canada I, Vancouver, June 2005. References
added in V
How Big Can Anomalous W Couplings Be?
Conventional wisdom has it that anomalous gauge-boson self-couplings can be
at most a percent or so in size. We test this wisdom by computing these
couplings at one loop in a generic renormalizable model of new physics. (For
technical reasons we consider the CP-violating couplings here, but our results
apply more generally.) By surveying the parameter space we find that the
largest couplings (several percent) are obtained when the new particles are at
the weak scale. For heavy new physics we compare our findings with expectations
based on an effective-lagrangian analysis. We find general patterns of induced
couplings which robustly reflect the nature of the underlying physics. We build
representative models for which the new physics could be first detected in the
anomalous gauge couplings.Comment: 40 pages, 11 figures, (dvi file and figures combined into a uuencoded
compressed file), (We correct an error in eq. 39 and its associated figure
(9). No changes at all to the text.), McGill-93/40, UQAM-PHE-93/03,
NEIPH-93-00
Supersymmetric Large Extra Dimensions and the Cosmological Constant: An Update
This article critically reviews the proposal for addressing the cosmological
constant problem within the framework of supersymmetric large extra dimensions
(SLED), as recently proposed in hep-th/0304256. After a brief restatement of
the cosmological constant problem, a short summary of the proposed mechanism is
given. The emphasis is on the perspective of the low-energy effective theory in
order to see how it addresses the problem of why low-energy particles like the
electron do not contribute too large a vacuum energy. This is followed by a
discussion of the main objections, which are grouped into the following five
topics:
(1) Weinberg's No-Go Theorem.
(2) Are hidden tunings of the theory required, and a problem?
(3) Why should the mechanism not rule out earlier epochs of inflation?
(4) How big are quantum effects, and which are the most dangerous?
(5) Can the mechanism be consistent with cosmological constraints?
It is argued that there are plausible reasons why the mechanism can thread
the potential objections, but that a definitive proof that it does depends on
addressing well-defined technical points. These points include identifying what
fixes the size of the extra dimensions, checking how topological obstructions
renormalize and performing specific calculations of quantum corrections. More
detailed studies of these issues, which are well reach within our present
understanding of extra-dimensional theories, are currently underway. As such,
the jury remains out concerning the proposal, although the prospects for
acquittal still seem good.Comment: 21 pages; an extended version of the contribution to the proceedings
of SUSY 2003, University of Arizona, Tucson AZ, June 2003, which has also
been updated to include developments since the conference. (v2 includes some
updated references and corrects a minor error in the bulk loop section
Charmless hadronic decays and new physics effects in the general two-Higgs doublet models
Based on the low-energy effective Hamiltonian with the generalized
factorization, we calculate the new physics contributions to the branching
ratios of the two-body charmless hadronic decays of and mesons
induced by the new gluonic and electroweak charged-Higgs penguin diagrams in
the general two-Higgs doublet models (models I, II and III). Within the
considered parameter space, we find that: (a) the new physics effects from new
gluonic penguin diagrams strongly dominate over those from the new -
and - penguin diagrams; (b) in models I and II, new physics contributions
to most studied B meson decay channels are rather small in size: from -15% to
20%; (c) in model III, however, the new physics enhancements to the
penguin-dominated decay modes can be significant, , and
therefore are measurable in forthcoming high precision B experiments; (d) the
new physics enhancements to ratios {\cal B}(B \to K \etap) are significant in
model III, , and hence provide a simple and plausible new
physics interpretation for the observed unexpectedly large B \to K \etap
decay rates; (e) the theoretical predictions for and
in model III are still consistent with the data
within errors; (f) the significant new physics enhancements to the
branching ratios of and decays are helpful to improve the
agreement between the data and the theoretical predictions; (g) the theoretical
predictions of in the 2HDM's are generally
consistent with experimental measurements and upper limits ()Comment: 55 pages, Latex file, 17 PS and EPS figures. With minor corrections,
final version to be published in Phys.Rev. D. Repot-no: PKU-TH-2000-4
Final-State Phases in Charmed Meson Two-Body Nonleptonic Decays
Observed decay rates indicate large phase differences among the amplitudes
for the charge states in and but
relatively real amplitudes in the charge states for . This
feature is traced using an SU(3) flavor analysis to a sign flip in the
contribution of one of the amplitudes contributing to the latter processes in
comparison with its contribution to the other two sets. This amplitude may be
regarded as an effect of rescattering and is found to be of magnitude
comparable to others contributing to charmed particle two-body nonleptonic
decays.Comment: 19 pages, latex, 4 figures, to be submitted to Phys. Rev.
Towards a Naturally Small Cosmological Constant from Branes in 6D Supergravity
We investigate the possibility of self-tuning of the effective 4D
cosmological constant in 6D supergravity, to see whether it could naturally be
of order 1/r^4 when compactified on two dimensions having Kaluza-Klein masses
of order 1/r. In the models we examine supersymmetry is broken by the presence
of non-supersymmetric 3-branes (on one of which we live). If r were
sub-millimeter in size, such a cosmological constant could describe the
recently-discovered dark energy. A successful self-tuning mechanism would
therefore predict a connection between the observed size of the cosmological
constant, and potentially observable effects in sub-millimeter tests of gravity
and at the Large Hadron Collider. We do find self tuning inasmuch as 3-branes
can quite generically remain classically flat regardless of the size of their
tensions, due to an automatic cancellation with the curvature and dilaton of
the transverse two dimensions. We argue that in some circumstances
six-dimensional supersymmetry might help suppress quantum corrections to this
cancellation down to the bulk supersymmetry-breaking scale, which is of order
1/r. We finally examine an explicit realization of the mechanism, in which
3-branes are inserted into an anomaly-free version of Salam-Sezgin gauged 6D
supergravity compactified on a 2-sphere with nonzero magnetic flux. This
realization is only partially successful due to a topological constraint which
relates bulk couplings to the brane tension, although we give arguments why
these relations may be stable against quantum corrections.Comment: 31 pages, 1 figure. Uses JHEP class. Expanded discussions in
Introduction, Section 3.2 (Quantum Corrections) and Section 4.2 (Topological
Constraint). Note added on subsequent related articles. Results unchange
Static quantities of the W boson in the SU_L(3) X U_X(1) model with right-handed neutrinos
The static electromagnetic properties of the boson, and
, are calculated in the SU_L(3)} \times U_X(1) model with
right-handed neutrinos. The new contributions from this model arise from the
gauge and scalar sectors. In the gauge sector there is a new contribution from
a complex neutral gauge boson and a singly-charged gauge boson .
The mass of these gauge bosons, called bileptons, is expected to be in the
range of a few hundreds of GeV according to the current bounds from
experimental data. If the bilepton masses are of the order of 200 GeV, the size
of their contribution is similar to that obtained in other weakly coupled
theories. However the contributions to both and are
negligible for very heavy or degenerate bileptons. As for the scalar sector, an
scenario is examined in which the contribution to the form factors is
identical to that of a two-Higgs-doublet model. It is found that this sector
would not give large corrections to and .Comment: New material included. Final version to apppear in Physical Review
A Phenomenological Study of the Process at High Energy Colliders and Measurement of the and Couplings
We perform a detailed study of the process including all contributions. The contributions other
than from real gauge boson production leads to a rich phenomenology. We explore
the use of the process as a means of precision measurement of the and
vertices. We concentrate on LEP II energies, GeV,
and energies appropriate to the proposed Next Linear Collider (NLC) high energy
collider with center of mass energies and 1~TeV. At 200
GeV, the process offers, at best, a consistency check of other processes being
considered at LEP200. At 500~GeV, the parameters ,
, , and can be measured to about or better at 95\% C.L. while at 1 TeV, they can be measured to about . At the high luminosities anticipated at high energy linear colliders
precision measurements are likely to be limited by systematic rather than
statistical errors.Comment: 33 pages, OCIP/C 93-18, UQAM-PHE-930
Dimension-six CP-violating operators of the third-family quarks and their effects at colliders
We listed all possible dimension-six CP-violating invariant operators involving the third-family quarks,
which can be generated by new physics at a higher energy scale. The expressions
of these operators after electroweak symmetry breaking and the induced
effective couplings , and
are also presented. We have evaluated sample contributions of these operators
to CP-odd asymmetries of transverse polarization of top quark in single top
production at the upgraded Tevatron, the similar effect in top-antitop pair
production at the NLC, and the CP-odd observables of momentum correlations
among the top quark decay products at the NLC. The energy and luminosity
sensitivity in probing these CP-violating new physics has also been studied.Comment: 24 pages, 2 figures adde
The fully differential single-top-quark cross section in next-to-leading order QCD
We present a new next-to-leading order calculation for fully differential
single-top-quark final states. The calculation is performed using phase space
slicing and dipole subtraction methods. The results of the methods are found to
be in agreement. The dipole subtraction method calculation retains the full
spin dependence of the final state particles. We show a few numerical results
to illustrate the utility and consistency of the resulting computer
implementations.Comment: 37 pages, latex, 2 ps figure