Probing Supergravity Models with Indirect Experimental Signatures

We explore the one-loop electroweak radiative corrections in the context of the traditional minimal $SU(5)$ and the string-inspired $SU(5)\times U(1)$ supergravity models by calculating explicitly vacuum-polarization and vertex-correction contributions to the $\epsilon_1$ and $\epsilon_b$ parameters. We also include in this analysis the constraint from $b\rightarrow s\gamma$ whose inclusive branching ratio $B(b\rightarrow s\gamma)$ has been actually measured very recently by CLEO. We find that by combining these three most important indirect experimental signatures and using the most recent experimental values for them, $m_t\gtrsim 170 {\rm GeV}$ is excluded for $\mu>0$ in both the minimal $SU(5)$ supergravity and the no-scale $SU(5)\times U(1)$ supergravity. We also find that $m_t\gtrsim 175(185) {\rm GeV}$ is excluded for any sign of $\mu$ in the minimal ($SU(5)\times U(1)$) supergravity model.Comment: RevTeX 3.0, 16 Pages+4 figures(not included but available as a uuencoded file from [email protected]), SNUTP-94-9

Zeroing In On the Top Quark, LSP and Scalar Higgs Masses

We estimate the top quark, lightest sparticle (LSP) and scalar higgs masses within a supersymmetric grand unified framework in which $\tan\beta \simeq m_t/m_b$ and the electroweak symmetry is radiatively broken. The requirement that the calculated $b$ quark mass lie close to its measured value, together with the cosmological constraint $\Omega_{LSP} \approx 1$, fixes the top quark mass to be $m_t(m_t) \approx 170 \pm 15\ GeV$. The LSP (of bino purity $\stackrel{_>}{_\sim} 98\%)$ has mass $\sim 200 - 350\ GeV$. In the scalar higgs sector the CP-odd scalar mass $m_A \stackrel{_<}{_\sim} 220\ GeV$. With $m_A \stackrel{_>}{_\sim} M_Z$, as suggested by the decay $b \rightarrow s\gamma$, we find $M_Z \stackrel{_<}{_\sim} m_{h^0} (m_{H^0}) \stackrel{_<}{_\sim} 140 (220)\ GeV$ and $120\ GeV \stackrel{_<}{_\sim} m_{H^\pm} \stackrel{_<}{_\sim} 240\ GeV$.Comment: 14 pages in plain LaTeX, BA-93-25, PRL-TH-93/

ϵb\epsilon_b Constraints on the Minimal SU(5)SU(5) and SU(5)×U(1)SU(5)\times U(1) Supergravity Models

We have performed a systematic analysis to compute the one-loop electroweak corrections to the Z->b b-bar vertex in terms of $\epsilon_b$ and $R_b$ in the context of the minimal $SU(5)$ and no-scale $SU(5)\times U(1)$ supergravity models. With the measured top mass, $m_t=174\pm 10^{+13}_{-12}$ \GeV , recently announced by CDF, we use the latest LEP data on $\epsilon_b$ and $R_b$ ($\equiv{\Gamma(Z->b b-bar)/{\Gamma(Z->hadrons)}}$) in order to constrain further the two models. We find that the present LEP data on $\epsilon_b$ and $R_b$ constrain the two models rather severely. Especially, the low-$\tan\beta$ region is constrained more severely. \tan\beta\lsim 2.5 $(4.0)$ is excluded by $\epsilon_b$ at $90\%$ C.~L. for m_t\gsim 170 $(180)$ \GeV in the minimal $SU(5)$ (no-scale $SU(5)\times U(1)$) supergravity. Even more stringent constraint comes from $R_b$. It excludes \tan\beta\lsim 4.0 at $90\%$ C.~L. for m_t\gsim 160 $(170)$ \GeV in the minimal $SU(5)$ (no-scale $SU(5)\times U(1)$) supergravity. We also find that the sign on $\mu$ in the two models can be determined from $\epsilon_b$ and $R_b$ at $90\%$ C.~L.Comment: RevTeX 3.0, 15 Pages+2 figures(not included but available as a uuencoded file from [email protected]), SNUTP-94-6

Squark and Slepton Mass Relations in Grand Unified Theories

In the minimal supersymmetric standard model, assuming universal scalar masses at large energies, there are four intragenerational relations between the masses of the squarks and sleptons for each light generation. In this paper we study the scalar mass relations which follow only from the assumption that at large energies there is a grand unified theory which leads to a significant prediction of the weak mixing angle. Two new intragenerational mass relations for each of the light generations are derived. In addition, a third mass relation is found which relates the Higgs masses, the masses of the third generation scalars , and the masses of the scalars of the lighter generations. Verification of a fourth mass relation, involvingonly the charged slepton masses, provides a signal for SO(10) unification.Comment: 29 pages, LateX, 2 uuencoded figures include

The phase difference between neural drives to antagonist muscles in essential tremor is associated with the relative strength of supraspinal and afferent input

The pathophysiology of essential tremor (ET), the most common movement disorder, is not fully understood. We investigated which factors determine the variability in the phase difference between neural drives to antagonist muscles, a long-standing observation yet unexplained. We used a computational model to simulate the effects of different levels of voluntary and tremulous synaptic input to antagonistic motoneuron pools on the tremor. We compared these simulations to data from 11 human ET patients. In both analyses, the neural drive to muscle was represented as the pooled spike trains of several motor units, which provides an accurate representation of the common synaptic input to motoneurons. The simulations showed that, for each voluntary input level, the phase difference between neural drives to antagonist muscles is determined by the relative strength of the supraspinal tremor input to the motoneuron pools. In addition, when the supraspinal tremor input to one muscle was weak or absent, Ia afferents provided significant common tremor input due to passive stretch. The simulations predicted that without a voluntary drive (rest tremor) the neural drives would be more likely in phase, while a concurrent voluntary input (postural tremor) would lead more frequently to an out-of-phase pattern. The experimental results matched these predictions, showing a significant change in phase difference between postural and rest tremor. They also indicated that the common tremor input is always shared by the antagonistic motoneuron pools, in agreement with the simulations. Our results highlight that the interplay between supraspinal input and spinal afferents is relevant for tremor generation

Reconciling Supersymmetric Grand Unification with αs(mZ)≈0.11\alpha_s(m_Z)\approx 0.11

We argue that supersymmetric grand unification of gauge couplings is not incompatible with small $\alpha_s$, even without large GUT-scale corrections, if one relaxes a usual universal gaugino mass assumption. A commonly assumed relation $M_2\simeq m_{\rm gluino}/3$ is in gross contradiction with $\alpha_s\approx 0.11$. Instead, small $\alpha_s$ favors $M_2\gg m_{\rm gluino}$. If this is indeed the case our observation casts doubt on another commonly used relation $M_1\simeq 0.5 M_2$ which originates from the same constraint of a common gaugino mass at the GUT scale. One firm prediction emerging within the small $\alpha_s$ scenario with the unconstrained gaugino masses is the existence of a relatively light gluino below $\sim$ 200\gev.Comment: 18 pages, LaTex format for text; epsf.sty needed for including 3 Postscript figures in the text. CHANGES: Comments on dark matter and non-minimal supergravity (see end of Sec. 2.3) and several references added; also some minor corrections made

Constraints on Baryon-Nonconserving Yukawa Couplings in a Supersymmetric Theory

The 1-loop evolution of couplings in the minimal supersymmetric standard model, extended to include baryon nonconserving $(B\!\!\!/)$ operators through explicit $R$-parity violation, is considered keeping only $B\!\!\!/$ superpotential terms involving the maximum possible number of third generation superfields. If all retained Yukawa couplings $Y_i$ are required to remain in the perturbative domain $(Y_i < 1)$ upto the scale of gauge group unification, upper bounds ensue on the magnitudes of the $B\!\!\!/$ coupling strengths at the supersymmetry breaking scale, independent of the model of unification. They turn out to be similar to the corresponding fixed point values reached from a wide range of $Y_i$ (including all $Y_i$ greater than unity) at the unification scale. The coupled evolution of the top and $B\!\!\!/$ Yukawa couplings results in a reduction of the fixed point value of the former.Comment: PRL-TH-94/8 and TIFR/TH/94-7, 15 pages, LaTe

Polarization of τ\tau lepton from scalar tau decay as a probe of neutralino mixing

The $\tau$ lepton arising from the scalar tau (\st) decay is naturally polarized. \ptau depends on the left--right mixing of the \st and the gaugino--higgsino mixing of the neutralino. The polarization \ptau could be measured from the energy distribution of the decay products of $\tau$ at future \epem colliders. A measurement of \ptauand of the \st production cross section allows to determine both these mixing angles.Comment: 20 pages Latex, 5 figures(not included). compressed ps file of the figures available at ftp://ftp.kek.jp/kek/preprints/TH/TH-425/fig.ps.g

Naturalness and superpartner masses or when to give up on weak scale supersymmetry

Superpartner masses cannot be arbitrarily heavy if supersymmetric extensions of the standard model explain the stability of the gauge hierarchy. This ancient and hallowed motivation for weak scale supersymmetry is often quoted, yet no reliable determination of this upper limit on superpartner masses exists. In this paper we compute upper bounds on superpartner masses in the minimal supersymmetric model, and we identify which values of the superpartner masses correspond to the most natural explanation of the hierarchy stability. We compare the most natural value of these masses and their upper limits to the physics reach of current and future colliders. As a result, we find that supersymmetry could explain weak scale stability naturally even if no superpartners are discovered at LEP II or the Tevatron (even with the Main Injector upgrade). However, we find that supersymmetry cannot provide a complete explanation of weak scale stability, if squarks and gluinos have masses beyond the physics reach of the LHC. Moreover, in the most natural scenarios, many sparticles, for example, charginos, squarks, and gluinos, lie within the physics reach of either LEP II or the Tevatron. Our analysis determines the most natural value of the chargino (squark) ((gluino)) mass consistent with current experimental constraints is $\sim$ 50 (250) ((250)) GeV and the corresponding theoretical upper bound is $\sim$ 250 (700) ((800)) GeV.Comment: 14 pages, LaTex, 17 figures uuencoded, gz-compressed file. Minor revisions bring archived manuscript in line with the published versio

Light Scalar Top and Heavy Top Signature at CDF

We propose a mechanism which could explain a slight excess of top signal rate recently reported by CDF in the framework of the supersymmetric standard model. If the scalar partner of the top (stop) is sufficiently light, the gluino with an appropriate mass could decay into the stop plus the top with almost 100\% branching ratio and experimental signatures of the gluino pair production could be indistinguishable from those of the top production in the present integrated luminosity Tevatron running. In this case the standard top signal, $W$ $+$ multi-jets events, would be effectively enhanced by the additional gluino contribution. It is shown, moreover, that such a mechanism can actually work in the radiative SU(2)$\times$U(1) breaking model without the GUT relations between the gaugino mass parameters.Comment: 8 pages (LaTeX), 3 figures not included (available on request) ; ITP-SU-94/03, RUP-94-0