Searcharxiv⌕ Search

arXiv subjects

Nir Polonsky

Publications and source records attributed to Nir Polonsky.

34 records · Page 2Linked to original sources
arXiv1997

Super-oblique corrections and non-decoupling of supersymmetry breaking

If supersymmetric partners of the known particles have masses at the multi-TeV scale, they will not be directly discovered at planned future colliders and decouple from most observables. However, such superpartners also induce non-decoupling effects that break the supersymmetric equivalence of gauge boson couplings $g_i$ and gaugino couplings $h_i$ through supersymmetric analogues of the oblique corrections. Working within well-motivated theoretical frameworks, we find that multi-TeV scale supersymmetric particles produce deviations at the 1-10% level in the ratios $h_i/g_i$. Such effects allow one to bound the scale of kinematically inaccessible superpartners through precision measurements of processes involving the accessible superparticles. Alternatively, if all superpartners are found, significant deviations imply the existence of highly split exotic supermultiplets.

hep-ph↗
arXiv1997

A wide scalar neutrino resonance and b\bar{b} production at LEP

In supersymmetric models with R-parity violation, scalar neutrinos may be produced as s-channel resonances in e^+e^- colliders. We note that within current constraints, the scalar neutrino may have a width of several GeV into b\bar{b} and be produced with large cross section, leading to a novel supersymmetry discovery signal at LEP II. In addition, if the scalar neutrino mass approximately equals m_Z, such a resonance necessarily increases R_b and reduces A_{FB}(b), significantly improving the fit to electroweak data. Bounds from B meson and top quark decays are leading constraints, and we stress the importance of future measurements.

hep-ph↗
arXiv1996

Supersymmetric Neutrino Masses, R Symmetries, and The Generalized mu Problem

In supersymmetric models a tree-level neutrino mass could originate from the (weak-scale) superpotential. We propose and examine a realization of that idea, which arises naturally in the framework of a spontaneously broken U(1) R-symmetry. The solution to the neutrino mass problem could shed light in this framework on the possible resolution of the $μ$ problem. Furthermore, the suppression of the neutrino mass in comparison to the weak scale arises dynamically and need not be encoded in the superpotential. The latter mechanism operates, for example, in universal models for the soft supersymmetry breaking terms. Phenomenological and cosmological implications of the model are also discussed, some of which are shown to hold more generally. We also note that future signatures could include observable enhancement of dijet and multijet production rates and a correlation between the supersymmetric and neutrino spectra.

hep-ph↗
arXiv1996

On Supersymmetric b-tau Unification, Gauge Unification, and Fixed Points

The equality assumption of the b and tau Yukawa couplings at the grand-unification scale can strongly constrain the allowed parameter space of supersymmetric models. We examine the constraints in the case that there is a discrepancy > 10% in the gauge coupling unification assumption (which necessarily implies large perturbations at the grand scale). The constraints are shown to diminish in that case [most significantly so if alpha_{s}(M_{Z}) \approx 0.11]. In particular, the requirement that the t Yukawa coupling, h_{t}, is near its quasi-fixed point may not be necessary. We discuss the colored-triplet threshold as a simple example of a source for the discrepancies, and comment on its possible implications. In addition, we point out that supersymmetric (as well as unification-scale) threshold corrections to h_{t} shift the fixed-point curve in the m_{t} - \tanβplane. The implications for the prediction of the Higgs boson mass are briefly discussed.

hep-ph↗
arXiv1995

The Light Higgsino-Gaugino Window

Supersymmetric models are typically taken to have $μ$ parameter and all soft supersymmetry breaking parameters at or near the weak scale. We point out that a small window of allowed values exists in which $μ$ and the electroweak gaugino masses are in the few GeV range. Such models naturally solve the supersymmetry $CP$ problem, can reduce the discrepancy in $R_b$, and suppress proton decay. In this window two neutralinos are in the few GeV range, two are roughly degenerate with the $Z^0$, and both charginos are roughly degenerate with the $W^{\pm}$ bosons. Such a signature cannot escape detection at LEP II. Models that fall in this window automatically arise from renormalizable hidden sectors in which hidden sector singlets participate only radiatively in supersymmetry breaking.

hep-ph↗
arXiv1995

The strong coupling, unification, and recent data

The prediction of the strong coupling assuming (supersymmetric) coupling constant unification is reexamined. We find, using the new electroweak data, $α_{s}(M_{Z}) \approx 0.129 \pm 0.010$. The implications of the large $α_{s}$ value are discussed. The role played by the $Z$ beauty width is stressed. It is also emphasized that high-energy (but not low-energy) corrections could significantly diminish the prediction. However, unless higher-dimension operators are assumed to be suppressed, at present one cannot place strong constraints on the super-heavy spectrum. Non-leading electroweak threshold corrections are also discussed.

hep-ph↗
arXiv1994

Unification and low-energy supersymmetry at one and two-loop orders

The status of coupling constant unification -- assuming the validity of the standard model or of its minimal supersymmetric extension at high energies -- and of relations between various Yukawa couplings (assuming the supersymmetri extension) which are implied in certain grand-unified theories, are studied in detail. Theoretical uncertainties in the calculations are emphasized, and low-energy constraints and predictions are derived. In particular, we find that bottom-tau unification favors a Higgs boson lighter than 110 GeV. The structure of the vacuum in the model studied is also discussed. Implications of embedding supersymmetric models in grand-unified theories are further explored and are shown to affect the soft supersymmetry breaking mass parameters of the models, and thus the spectrum at low-energy.

hep-ph↗
arXiv1994

Non-Universal GUT Corrections to the Soft Terms and their Implications in Supergravity Models

Potentially large non-universal corrections to the soft supersymmetry breaking parameters arise from their evolution between the Planck and the grand-unification scales. We detail typical patterns of non-universality in GUT models, as well as elaborate on their propagation to the weak scale and on their low-energy implications. Possible corrections to the different scalar quark and lepton masses and the Higgs and the gaugino-Higgsino sector parameters are described in detail, and new allowed regions of the parameter space are pointed out. In particular, the patterns studied often lead to heavier Higgsinos and $t$-scalar. One-loop GUT threshold corrections to the soft parameters are also discussed and shown to be important.

hep-ph↗
arXiv1994

An Upper Bound on the Higgs Boson Mass from Yukawa Unification and a Comment on Vacuum Stability Constraints

Only small regions in the $m_{t} - \tanβ$ plane are allowed when considering simultaneously (assuming the MSSM) coupling constant unification and (minimal) GUT relations among Yukawa couplings (i.e., $h_{b} = h_τ$ at the unification point). In particular, if $m_{t} \simle 175$ GeV we find that only $1 \simle \tanβ\simle 1.5$ or $\tanβ\simgr 40 \pm 10$ is allowed. The former implies that the light Higgs boson is $\simle 110$ GeV and, in principle, visible to LEPII. The prediction for the Higgs boson mass in the $\tanβ\approx 1$ scenario is discussed and uncertainties related to ($i$) vacuum stability constraints, ($ii$) different methods for calculating the Higgs boson mass, ($iii$) two-loop calculations and ($iv$) GUT corrections are briefly reviewed. It is shown that large left-right mixing between the $t$-scalars can significantly enhance the Higgs boson mass. That and an ambiguity in the size of the two-loop correction lead to our conservative upper bound of 110 GeV. Vacuum stability considerations constrain the $t$-scalar mixing and slightly diminish the upper bound (depending on the value of $m_{t}$). Improved two-loop calculations are also expected to strengthen the bound.

hep-ph↗
arXiv1994

GUT effects in the soft supersymmetry breaking terms

In minimal supergravity theories the soft supersymmetry breaking (SSB) parameters are universal (flavor blind) near the Planck scale. Nevertheless, one often assumes universality at the grand-unification scale $M_{G} \approx 10^{16}$ GeV instead, and corrections to the SSB parameters arising from their evolution between the Planck and GUT scales are neglected. We study these corrections and show that large splittings between the scalar mass parameters can be induced at $M_{G}$. These effects are model dependent and lead to significant uncertainties in the low-energy predictions of supersymmetric models, in their correlations and in the allowed parameter space.

hep-ph↗
arXiv1994

Implications of Yukawa unification for the Higgs sector in supersymmetric grand-unified models

The SU(5) unification-scale relation h_b=h_tau between the b and tau Yukawa couplings severely constrains tan beta and m_t (even more so if h_t=h_b= h_tau holds) in supersymmetric models. We examine the implications of these constraints for the Higgs sector assuming universal soft breaking terms, and emphasize that both of these relations impose unique characteristics in terms of symmetries and of the spectrum. We further study the tan beta near 1 scenario, which is suggested by h_b=h_tau, and, in particular, the loop- induced mass of the light Higgs boson. We compare the effective potential and renormalization group methods and stress the two-loop ambiguities in the calculation of the mass. These and a large enhancement to the loop correction due to t-scalar left-right mixing considerably weaken the upper bound. Nevertheless, we find that for this scenario the Higgs boson is probably lighter than 110 GeV, and typically lighter than 100 GeV. Thus, it is in the mass range that may be relevant for LEPII. Our numerical results are presented in a self-contained manner in section V. In separate appendices we discuss the global symmetries of the Higgs potential, the issue of false (color-breaking) vacua, two-loop calculations, and the effect of an additional Higgs singlet. We show that the approximate constraints that are often used to eliminate color-breaking vacua are not always relevant.

hep-ph↗
arXiv1993

Precision Data Parameters and Grand Unification Predictions

When realizing the Minimal Supersymmetric Standard Model (MSSM) within a (simple) Grand Unified Theory (GUT), the predicted ranges for the strong coupling and the ratio of two Higgs doublet expectation values are strongly correlated with the weak angle and the $t$-quark mass. (The latter are extracted from precision data.) We spell out those relations and point out the implication for the mass of the light MSSM (CP even) Higgs boson.

hep-ph↗
arXiv1993

Coupling Constant and Yukawa Coupling Unifications: Uncertainties and Constraints

The status of coupling constant unification (with and without a unification of Yukawa couplings) is discussed. Uncertainties associated with the input coupling constants, $m_{b}$ and $m_{t}$, threshold corrections at the low and high scale, and possible nonrenormalizable operators are described and a discrepancy between effective and physical scales is pointed out. Theoretical uncertainties in the predictions of $α_{s}(M_{Z})$, $m_{b}$, and the unification scale, $M_{G}$, are discussed and estimated. Constraints on the super-partner spectrum are found to be weak if uncertainties associated with the high-scale are included. However, requiring $h_{b} = h_τ$ at $M_{G}$ excludes $3 < \tan β< 40$ (for $m_{t} < 200$ GeV).

hep-ph↗
arXiv1993

The Bottom Mass Prediction in Supersymmetric Grand Unification; Uncertainties and Constraints

Grand unified theories often predict unification of Yukawa couplings (e.g., $h_{b} = h_τ$), and thus certain relations among fermion masses. The latter can distinguish these from models that predict only coupling constant unification. The implications of Yukawa couplings of the heavy-family in the supersymmetric extension of the standard model (when embedded in a GUT) are discussed. In particular, uncertainties associated with $m_{t}$ and $m_{b}$, threshold corrections at the low-scale, and threshold and nonrenormalizable-operator corrections associated with a grand-unified sector at the high-scale are parametrized and estimated. The implication of these and of the correlation between $m_{t}$ and the prediction for $α_{s}$ are discussed. Constraints on the $\tanβ$ range in such models and an upper bound on the $t$-quark pole mass are given and are shown to be affected by the $α_{s}-m_{t}$ correlation. Constraints on the low-scale thresholds are found to be weakened by uncertainties associated with the high-scale.

hep-ph↗
arXiv1992

Uncertainties in Coupling Constant Unification

The status of coupling constant unification in the standard model and its supersymmetric extension are discussed. Uncertainties associated with the input coupling constants, $m_{t}$, threshold corrections at the low and high scales, and possible nonrenormalizable operators are parametrized and estimated. A simple parametrization of a general supersymmetric new particle spectrum is given. It is shown that an effective scale $M_{SUSY}$ can be defined, but for a realistic spectrum it may differ considerably from the typical new particle masses. The implications of the lower (higher) values of $α_{s}(M_{Z})$ suggested by low-energy ($Z$-pole) experiments are discussed.

hep-ph↗