1,217 research outputs found
Electroweak Constraints from Atomic Parity Violation and Neutrino Scattering
Precision electroweak physics can provide fertile ground for uncovering new
physics beyond the Standard Model (SM). One area in which new physics can
appear is in so-called "oblique corrections", i.e., next-to-leading order
expansions of bosonic propagators corresponding to vacuum polarization. One may
parametrize their effects in terms of quantities and that discriminate
between conservation and non-conservation of isospin. This provides a means of
comparing the relative contributions of precision electroweak experiments to
constraints on new physics. Given the prevalence of strongly -sensitive
experiments, there is an acute need for further constraints on , such as
provided by atomic parity-violating experiments on heavy atoms. We evaluate
constraints on arising from recently improved calculations in the Cs atom.
We show that the top quark mass provides stringent constraints on
within the context of the Standard Model. We also consider the potential
contributions of next-generation neutrino scattering experiments to improved
constraints.Comment: 10 pages, 4 figures, final corrected version to be published in
Physical Review
Tachyon Vacuum in Cubic Superstring Field Theory
In this paper we give an exact analytic solution for tachyon condensation in
the modified (picture 0) cubic superstring field theory. We prove the absence
of cohomology and, crucially, reproduce the correct value for the D-brane
tension. The solution is surprising for two reasons: First, the existence of a
tachyon vacuum in this theory has not been definitively established in the
level expansion. Second, the solution {\it vanishes} in the GSO sector,
implying a ``tachyon vacuum'' solution exists even for a {\it BPS} D-brane.Comment: 16 pages, 2 figure
The Prediction of Mass of Z'-Boson from Mixing
B_q^0-B_^0 bar mixing offers a profound probe into the effects of new
physics beyond the Standard Model. In this paper, and
mass differences are considered taking the effect of both
Z-and Z' -mediated flavour-changing neutral currents in the
mixing (q = d, s). Our estimated mass of Z' boson is accessible at the
experiments LHC and B-factories in near future.Comment: 11 pages, 02 Figure
Recent Developments in Precision Electroweak Physics
Developments in precision electroweak physics in the two years since the
symposium are briefly summarized.Comment: Update on recent developments, prepared for the publication of the
Proceedings of Alberto Sirlin Symposium, New York University, October 2000.
10 pages, 1 figur
The Fourth SM Family Neutrino at Future Linear Colliders
It is known that Flavor Democracy favors the existence of the fourth standard
model (SM) family. In order to give nonzero masses for the first three family
fermions Flavor Democracy has to be slightly broken. A parametrization for
democracy breaking, which gives the correct values for fundamental fermion
masses and, at the same time, predicts quark and lepton CKM matrices in a good
agreement with the experimental data, is proposed. The pair productions of the
fourth SM family Dirac and Majorana neutrinos at future
linear colliders with GeV, 1 TeV and 3 TeV are considered. The
cross section for the process
and the branching ratios for possible decay modes of the both neutrinos are
determined. The decays of the fourth family neutrinos into muon channels
provide cleanest signature at
colliders. Meanwhile, in our parametrization this channel is
dominant. bosons produced in decays of the fourth family neutrinos will be
seen in detector as either di-jets or isolated leptons. As an example we
consider the production of 200 GeV mass fourth family neutrinos at
GeV linear colliders by taking into account di-muon plus
four-jet events as signatures.Comment: 16 pages, 3 figures, 10 table
Relevant Deformations in Open String Field Theory: a Simple Solution for Lumps
We propose a remarkably simple solution of cubic open string field theory
which describes inhomogeneous tachyon condensation. The solution is in
one-to-one correspondence with the IR fixed point of the RG-flow generated in
the two--dimensional world-sheet theory by integrating a relevant operator with
mild enough OPE on the boundary. It is shown how the closed string overlap
correctly captures the shift in the closed string one point function between
the UV and the IR limits of the flow. Examples of lumps in non-compact and
compact transverse directions are given.Comment: 45 pages. v2: typos and minor improvements. v3: submitted to jhe
Probing Z' gauge boson with the spin configuration of top quark pair production at future linear colliders
We explore the effects of extra neutral gauge boson involved in the
supersymmetric E6 model on the spin configuration of the top quark pair
produced at the polarized e- e+ collider. Generic mixing terms are considered
including kinetic mixing terms as well as mass mixing. In the off-diagonal spin
basis of the standard model, we show that the cross sections for the suppressed
spin configurations can be enhanced with the effects of the Z' boson through
the modification of the spin configuration of produced top quark pair enough to
be measured in the Linear Colliders, which provides the way to observe the
effects of Z' boson and discriminate the pattern of gauge group decomposition.
It is pointed out that the kinetic mixing may dilute the effects of mass mixing
terms, and we have to perform the combined analysis.Comment: 19 pages including 5 figures, ReVTe
The energy of the analytic lump solution in SFT
In a previous paper a method was proposed to find exact analytic solutions of
open string field theory describing lower dimensional lumps, by incorporating
in string field theory an exact renormalization group flow generated by a
relevant operator in a worldsheet CFT. In this paper we compute the energy of
one such solution, which is expected to represent a D24 brane. We show, both
numerically and analytically, that its value corresponds to the theoretically
expected one.Comment: 45 pages, former section 2 suppressed, Appendix D added, comments and
references added, typos corrected. Erratum adde
Indications for an Extra Neutral Gauge Boson in Electroweak Precision Data
A new analysis of the hadronic peak cross section at LEP 1 implies a small
amount of missing invisible width in Z decays, while the effective weak charge
in atomic parity violation has been determined recently to 0.6% accuracy,
indicating a significantly negative S parameter. As a consequence of these two
deviations, the data are described well if the presence of an additional Z'
boson, such as predicted in Grand Unified Theories, is assumed. Moreover, the
data are now rich enough to study an arbitrary extra Z' boson and to determine
its couplings in a model independent way. An excellent best fit to the data is
obtained in this case, suggesting the possibility of a family non-universal Z'
with properties similar to ones predicted in a class of superstring theories.Comment: 5 pages of ReVTeX, 2 figure
Ghost story. III. Back to ghost number zero
After having defined a 3-strings midpoint-inserted vertex for the bc system,
we analyze the relation between gh=0 states (wedge states) and gh=3 midpoint
duals. We find explicit and regular relations connecting the two objects. In
the case of wedge states this allows us to write down a spectral decomposition
for the gh=0 Neumann matrices, despite the fact that they are not commuting
with the matrix representation of K1. We thus trace back the origin of this
noncommutativity to be a consequence of the imaginary poles of the wedge
eigenvalues in the complex k-plane. With explicit reconstruction formulas at
hand for both gh=0 and gh=3, we can finally show how the midpoint vertex avoids
this intrinsic noncommutativity at gh=0, making everything as simple as the
zero momentum matter sector.Comment: 40 pages. v2: typos and minor corrections, presentation improved in
sect. 4.3, plots added in app. A.1, two refs added. To appear in JHE
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