3,815 research outputs found

### A search for exact superstring vacua

We investigate $2d$ sigma-models with a $2+N$ dimensional Minkowski signature
target space metric and Killing symmetry, specifically supersymmetrized, and
see under which conditions they might lead to corresponding exact string vacua.
It appears that the issue relies heavily on the properties of the vector
$M_{\mu}$, a reparametrization term, which needs to possess a definite form for
the Weyl invariance to be satisfied. We give, in the $n = 1$ supersymmetric
case, two non-renormalization theorems from which we can relate the $u$
component of $M_{\mu}$ to the $\beta^G_{uu}$ function. We work out this $(u,u)$
component of the $\beta^G$ function and find a non-vanishing contribution at
four loops. Therefore, it turns out that at order $\alpha^{\prime 4}$, there
are in general non-vanishing contributions to $M_u$ that prevent us from
deducing superstring vacua in closed form.Comment: 9 pages, latex, CERN-TH.6946/9

### Explicit supertring vacua in a background of gravitational waves and dilaton

We present an explicit solution of superstring effective equations,
represented by gravitational waves and dilaton backgrounds. Particular
solutions will be examined in a forthcoming note.Comment: 10 pages, latex, CERN-TH.7373/9

### 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

### No-scale supergravity confronts LEP diphoton events

We examine the possibility that some anomalous acoplanar diphoton events
observed at LEP may be consistent with the predictions of our previously
proposed one-parameter no-scale supergravity model with a light gravitino, via
the process e^+e^- -> chi chi -> gamma gamma+E_miss. We find that one such
event may indeed be consistent with the model predictions for m_chi \approx
(60-70) GeV. This region of parameter space is also consistent with the
selectron and chargino interpretations of the CDF ee gamma gamma + E_T,miss
event.Comment: 9 pages, LaTeX, 4 figures (included). Updated to include full LEP161
dat

### Unexpected features of e+e-->ppbar and e+e-->lambda-lambdabar cross sections near threshold

Unexpected features of the BaBar data on e+e- in baryon-antibaryon cross
sections are discussed. These data have been collected, with unprecedented
accuracy, by means of the initial state radiation technique, which is
particularly suitable in giving good acceptance and energy resolution at
threshold. A striking feature observed in the BaBar data is the non-vanishing
cross section at threshold for all these processes. This is the expectation due
to the Coulomb enhancement factor acting on a charged fermion pair. In the case
of e+e- in proton-antiproton it is found that Coulomb final state interactions
largely dominate the cross section and the form factor is |G^p(4M^2_p)|~1,
which could be a general feature for baryons. In the case of neutral baryons an
interpretation of the non-vanishing cross section at threshold is suggested,
based on quark electromagnetic interaction and taking into account the
asymmetry between attractive and repulsive Coulomb factors. Besides strange
baryon cross sections are compared to U-spin invariance predictions.Comment: 12 pages, 11 figure

### 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
$SU(5)\times U(1)$ 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 $SU(N,1)$ no-scale supergravity model and a
dilaton-induced supersymmetry breaking scenario. Both imply universal soft
supersymmetry breaking parameters: $m_0=0, A=0$ 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: $m_t$, $\tan\beta$, and $m_{\tilde g}$.
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 $\tan\beta$ in terms of
$m_t,m_{\tilde g}$. In the strict no-scale case we find that the value of $m_t$
determines the sign of $\mu$ (\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,
$\tan\beta\approx1.4-1.6$ 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

### The SuperWorlds of SU(5) and SU(5)xU(1): A Critical Assessment and Overview

We present an overview of the simplest supergravity models which enforce
radiative breaking of the electroweak symmetry, namely the minimal $SU(5)$
supergravity model and the class of string-inspired/derived supergravity models
based on the flipped $SU(5)\times U(1)$ structure supplemented by a minimal set
of additional matter representations such that unification occurs at the string
scale (\sim10^{18}\GeV). These models can be fully parametrized in terms of
the top-quark mass, the ratio $\tan\beta=v_2/v_1$, and three supersymmetry
breaking parameters ($m_{1/2},m_0,A$). The latter are chosen in the minimal
$SU(5)$ model such that the stringent constraints from proton decay and
cosmology are satisfied. In the flipped $SU(5)$ case we consider two
string-inspired supersymmetry breaking scenaria: $SU(N,1)$ no-scale
supergravity and a dilaton-induced supersymmetry breaking scenario. Both imply
universal soft supersymmetry breaking parameters: $m_0=A=0$ and
m_0=\coeff{1}{\sqrt{3}}m_{1/2}, A=-m_{1/2} respectively. We present a
comparative study of the sparticle and Higgs spectra of both flipped $SU(5)$
models and the minimal $SU(5)$ model and conclude that all can be partially
probed at the Tevatron and LEPII (and the flipped models at HERA too). In both
flipped $SU(5)$ cases there is a more constrained version which allows to
determine $\tan\beta$ in terms of $m_t,m_{\tilde g}$ and which leads to much
sharper and readily accessible experimental predictions. We also discuss the
prospects for indirect experimental detection: a non-trivial fraction of the
parameter space of the flipped $SU(5)$ models is in conflict with the present
experimental allowed range for the $b\to s\gamma$ rare decay mode, and the
one-loop electroweak radiative corrections imply the 90\% CL upper boundComment: CERN-TH.6934/93, CTP-TAMU-34/93, LaTeX, 58 pages, 20 embedded
figures. Complete ps file (~12000 blocks, 5.24MB) available via anonymous ftp
from site tamsun.tamu.edu in directory incoming, filename: CTP-TAMU-34-93.p

### The strongest experimental constraints on SU(5)xU(1) supergravity models

We consider a class of well motivated string-inspired flipped $SU(5)$
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 $(m_t,\tan\beta,m_{\tilde
g})$. We show that the LEP precise measurements of the electroweak parameters
in the form of the $\epsilon_1$ 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 $\epsilon_1$ constraint (at
90(95)\%CL) requires the presence of light charginos
(m_{\chi^\pm_1}\lsim50-100\GeV depending on $m_t$). Since all sparticle
masses are proportional to $m_{\tilde g}$, 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 $SU(5)$
supergravity model. The \bsg constraint excludes a significant fraction of
the otherwise allowed region in the $(m_{\chi^\pm_1},\tan\beta)$ 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
$\epsilon_1$ 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]

### New phenomena in the standard no-scale supergravity model

We revisit the no-scale mechanism in the context of the simplest no-scale
supergravity extension of the Standard Model. This model has the usual
five-dimensional parameter space plus an additional parameter $\xi_{3/2}\equiv
m_{3/2}/m_{1/2}$. We show how predictions of the model may be extracted over
the whole parameter space. A necessary condition for the potential to be stable
is ${\rm Str}{\cal M}^4>0$, which is satisfied if \bf m_{3/2}\lsim2 m_{\tilde
q}. Order of magnitude calculations reveal a no-lose theorem guaranteeing
interesting and potentially observable new phenomena in the neutral scalar
sector of the theory which would constitute a ``smoking gun'' of the no-scale
mechanism. This new phenomenology is model-independent and divides into three
scenarios, depending on the ratio of the weak scale to the vev at the minimum
of the no-scale direction. We also calculate the residual vacuum energy at the
unification scale ($C_0\, m^4_{3/2}$), and find that in typical models one must
require $C_0>10$. Such constraints should be important in the search for the
correct string no-scale supergravity model. We also show how specific classes
of string models fit within this framework.Comment: 11pages, LaTeX, 1 figure (included), CERN-TH.7433/9

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