5,607 research outputs found
A Layman's guide to SUSY GUTs
The determination of the most straightforward evidence for the existence of
the Superworld requires a guide for non-experts (especially experimental
physicists) for them to make their own judgement on the value of such
predictions. For this purpose we review the most basic results of Super-Grand
unification in a simple and clear way. We focus the attention on two specific
models and their predictions. These two models represent an example of a direct
comparison between a traditional unified-theory and a string-inspired approach
to the solution of the many open problems of the Standard Model. We emphasize
that viable models must satisfy {\em all} available experimental constraints
and be as simple as theoretically possible. The two well defined supergravity
models, and , can be described in terms of only a few
parameters (five and three respectively) instead of the more than twenty needed
in the MSSM model, \ie, the Minimal Supersymmetric extension of the Standard
Model. A case of special interest is the strict no-scale
supergravity where all predictions depend on only one parameter (plus the
top-quark mass). A general consequence of these analyses is that supersymmetric
particles can be at the verge of discovery, lurking around the corner at
present and near future facilities. This review should help anyone distinguish
between well motivated predictions and predictions based on arbitrary choices
of parameters in undefined models.Comment: 25 pages, Latex, 11 figures (not included), CERN-TH.7077/93,
CTP-TAMU-65/93. A complete ps file (1.31MB) with embedded figures is
available by request from [email protected]
First Constraints on SU(5)xU(1) Supergravity from Trilepton Searches at the Tevatron
We present the first constraints on the parameter space of
supergravity (in both no-scale and dilaton scenarios) which arise from the
recently announced limits on trilepton searches at the Tevatron. The trilepton
rate has been calculated for those points in parameter space which satisfy not
only the minimal theoretical and experimental LEP constraints, but also the
{\em combined} effect of the following indirect experimental constraints: (i)
the CLEO limits on the rate, (ii) the long-standing limit on the
anomalous magnetic moment of the muon, (iii) the non-observation of anomalous
muon fluxes in underground detectors (``neutrino telescopes"), and (iv) the
electroweak LEP high-precision measurements in the form of the
parameters. For m_t=150\GeV, the trilepton
constraint rules out some regions of parameter space with chargino masses as
high as m_{\chi^\pm_1}\approx105\GeV, although it is not possible to
establish a new absolute lower bound on the chargino mass. For m_t=170\GeV,
the simultaneous imposition of {\em all} of the above constraints excludes the
dilaton scenario completely, and leaves only a few allowed points in parameter
space in the no-scale scenario (with m_{\tilde q}\approx m_{\tilde
g}\lsim285\GeV). The five-fold increase in integrated luminosity expected in
the upcoming Tevatron run should probe some regions of parameter space with
chargino masses much beyond the reach of LEPII.Comment: 9 pages, 5 figures, latex. Figures available as 0.540MB uuencoded
file from [email protected]. CERN-TH.7107/93, CTP-TAMU-72/9
in supergravity models
We compute the supersymmetric contribution to
in a
variety of supergravity models. We find R^{\rm susy}_b\lsim0.0004, which does
not shift significantly the Standard Model prediction
( for m_t=160\GeV). An improvement in experimental
precision by a factor of four would be required to be sensitive to such an
effect.Comment: 5 pages, LaTeX, 1 figure (included)
The strongest experimental constraints on SU(5)xU(1) supergravity models
We consider a class of well motivated string-inspired flipped
supergravity models which include four supersymmetry breaking scenarios:
no-scale, strict no-scale, dilaton, and special dilaton, such that only three
parameters are needed to describe all new phenomena . We show that the LEP precise measurements of the electroweak parameters
in the form of the variable, and the CLEOII allowed range for
\bsg are at present the most important experimental constraints on this class
of models. For m_t\gsim155\,(165)\GeV, the constraint (at
90(95)\%CL) requires the presence of light charginos
(m_{\chi^\pm_1}\lsim50-100\GeV depending on ). Since all sparticle
masses are proportional to , m_{\chi^\pm_1}\lsim100\GeV
implies: m_{\chi^0_1}\lsim55\GeV, m_{\chi^0_2}\lsim100\GeV, m_{\tilde
g}\lsim360\GeV, m_{\tilde q}\lsim350\,(365)\GeV, m_{\tilde
e_R}\lsim80\,(125)\GeV, m_{\tilde e_L}\lsim120\,(155)\GeV, and
m_{\tilde\nu}\lsim100\,(140)\GeV in the no-scale (dilaton) flipped
supergravity model. The \bsg constraint excludes a significant fraction of
the otherwise allowed region in the plane
(irrespective of the magnitude of the chargino mass), while future experimental
improvements will result in decisive tests of these models. In light of the
constraint, we conclude that the outlook for chargino and
selectron detection at LEPII and at HERA is quite favorable in this class of
models.Comment: CTP-TAMU-40/93, Latex, 13 pages, 10 figures (available as uuencoded
0.963MB file from [email protected]
A New Supersensitive Flame Detector and its Use for Early Forest Fire Detection
A new flame detector, three orders of magnitude more powerful than the
existing ones, is presented. This detector needs to be mass-produced for its
use in order to be incorporated in an early forest fire detection system. A
project able to implement its use to overcome the forest fire emergency is
described
The top-quark mass in SU(5)xU(1) supergravity
We show that the currently experimentally preferred values of the top-quark
mass (\ie, 130\lsim m_t\lsim180\GeV) are naturally understood in the context
of string models, where the top-quark Yukawa coupling at the string scale is
generically given by , with the unified gauge
coupling. A detailed study of the Yukawa sector of
supergravity shows that the ratio of the bottom-quark to tau-lepton Yukawa
couplings at the string scale is required to be in the range
0.7\lsim\lambda_b/\lambda_\tau\lsim1, depending on the values of and
. This result is consistent with symmetry, which does
{\em not} require the equality of these Yukawa couplings in the unbroken
symmetry phase of the theory. As a means of possibly predicting the value of
, we propose a procedure whereby the size of the allowed parameter space
is determined as a function of , since all sparticle and Higgs-boson
masses and couplings depend non-trivially on . At present, no significant
preference for particular values of in supergravity is
observed, except that high-precision LEP data requires m_t\lsim180\GeV.Comment: latex, 10 pages, 4 figures (included), CERN-TH.7138/94,
CTP-TAMU-05/9
New Precision Electroweak Tests of SU(5) x U(1) Supergravity
We explore the one-loop electroweak radiative corrections in supergravity via explicit calculation of vacuum-polarization and
vertex-correction contributions to the and
parameters. Experimentally, these parameters are obtained from a global fit to
the set of observables , and . We
include -dependent effects, which induce a large systematic negative shift
on for light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). The
(non-oblique) supersymmetric vertex corrections to \Zbb, which define the
parameter, show a significant positive shift for light chargino
masses, which for can be nearly compensated by a negative
shift from the charged Higgs contribution. We conclude that at the 90\%CL, for
m_t\lsim160\GeV the present experimental values of and
do not constrain in any way supergravity in
both no-scale and dilaton scenarios. On the other hand, for m_t\gsim160\GeV
the constraints on the parameter space become increasingly stricter. We
demonstrate this trend with a study of the m_t=170\GeV case, where only a
small region of parameter space, with \tan\beta\gsim4, remains allowed and
corresponds to light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). Thus
supergravity combined with high-precision LEP data would
suggest the presence of light charginos if the top quark is not detected at the
Tevatron.Comment: LaTeX, 11 Pages+4 Figures(not included), the figures available upon
request as an uuencoded file(0.4MB) or 4 PS files from [email protected],
CERN-TH.7078/93, CTP-TAMU-68/93, ACT-24/9
SU(5)xU(1): a string paradigm of a TOE and its experimental consequences
We present a string-inspired/derived supergravity model based on the flipped
structure supplemented by a minimal set of additional matter
representations such that unification occurs at the string scale
(\sim10^{18}\GeV). This model is complemented by two string supersymmetry
breaking scenaria: the no-scale supergravity model and a
dilaton-induced supersymmetry breaking scenario. Both imply universal soft
supersymmetry breaking parameters: and
m_0=\coeff{1}{\sqrt{3}}m_{1/2}, A=-m_{1/2} respectively. In either case the
models depend on only three parameters: , , and .
We present a comparative study of the sparticle and Higgs spectra of both
models and conclude that even though both can be partially probed at the
Tevatron, LEPII, and HERA, a larger fraction of the parameter space of the
no-scale model is actually accessible. In both cases there is a more
constrained version which allows to determine in terms of
. In the strict no-scale case we find that the value of
determines the sign of (\mu>0:\,m_t\lsim135\GeV,
\mu<0:\,m_t\gsim140\GeV) and whether the lightest Higgs boson mass is above
or below 100\GeV. In the more constrained version of the dilaton scenario,
and m_t\lsim155\GeV, 61\GeV\lsim m_h\lsim91\GeV
follow. Thus, continuing Tevatron top-quark searches and LEPI,II Higgs searches
could probe this restricted scenario completely.Comment: CERN-TH.6926/93, CTP-TAMU-33/93, LaTeX, 33 pages, 11 embedded
figures. Significant numerical correction to the dilaton scenario. Complete
ps file (7943 blocks,3.33MB) available via anonymous ftp from site
tamsun.tamu.edu in directory incoming, filename: CTP-TAMU-33-93.p
Precision Electroweak Tests of the Minimal and Flipped SU(5) Supergravity Models
We explore the one-loop electroweak radiative corrections in the minimal
and the no-scale flipped supergravity models via explicit
calculation of vacuum polarization contributions to the
parameters. Experimentally, are obtained from a global fit
to the LEP observables, and measurements. We include -dependent
effects which have been neglected in most previous ``model-independent"
analyses of this type. These effects induce a large systematic negative shift
on for light chargino masses (m_{\chi^\pm_1}\lsim70\GeV).
In agreement with previous general arguments, we find that for increasingly
large sparticle masses, the heavy sector of both models rapidly decouples, \ie,
the values for quickly asymptote to the Standard Model
values with a {\it light} Higgs (m_{H_{SM}}\sim100\GeV). Specifically, at
present the CL upper limit on the top-quark mass is m_t\lsim175\GeV in
the no-scale flipped supergravity model. These bounds can be
strengthened for increasing chargino masses in the 50-100\GeV interval. In
particular, for m_t\gsim160\GeV, the Tevatron may be able to probe through
gluino() and squark() production up to m_{\tilde g}\approx
m_{\tilde q}\approx250\GeV, exploring at least half of the parameter space in
this model.Comment: 15 pages,(6 ps figures available upon request), TeX(harvmac),
CTP-TAMU-19/93, ACT-07/9
- …