arXiv subjects

Jonathan L. Feng

Publications and source records attributed to Jonathan L. Feng.

177 records · Page 10Linked to original sources

arXiv1998

Third Generation Familons, B Factories, and Neutrino Cosmology

We study the physics of spontaneously broken family symmetries acting on the third generation. Massless familons (or Majorons) $f$ associated with such broken symmetries are motivated especially by cosmological scenarios with decaying tau neutrinos. We first note that, in marked contrast with the case for the first two generations, constraints on third generation familon couplings are poor, and are, in fact, non-existent at present in the hadronic sector. We derive new bounds from $B^0$--$\bar{B}^0$ mixing, $B^0 \to l^+ l'^-$, $b\to sν\barν$, and astrophysics. The resulting constraints on familon decay constants are still much weaker than those for the first and second generation. We then discuss the promising prospects for significant improvements from searches for $τ\to l f$, $B\to (π, K) f$, and $b\to (d,s) f$ with the current CLEO, ARGUS, and LEP data. Finally, we note that future constraints from CLEO III and the $B$ factories will probe decay constants beyond 10^8 GeV, well within regions of parameter space favored by proposed scenarios in neutrino cosmology.

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arXiv1998

R-Parity Violation and Sneutrino Resonances at Muon Colliders

In supersymmetric models with R-parity violation, sneutrinos may be produced as s-channel resonances at muon colliders. We demonstrate that, for R-parity violating couplings as low as 10^-4, sneutrino resonances may be observed and may be exploited to yield high precision SUSY parameter measurements. The excellent beam energy resolution of muon colliders may also be used to resolve MeV level splittings between CP-even and CP-odd sneutrino mass eigenstates.

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arXiv1997

New Probes of Supersymmetry Beyond the Minimal Framework

If supersymmetry is discovered at future colliders, what can we learn? While our appreciation of the variety of possible supersymmetric models has grown tremendously in recent years, most attempts to answer this question have been in the context of some simple and highly restrictive framework, such as minimal supergravity. In this talk I describe new probes of phenomena that are generic in models beyond the minimal framework. These include tests of supersymmetric flavor and CP violation and probes of kinematically inaccessible superparticle sectors through ``super-oblique corrections.'' Such probes have wide applicability to distinguishing models, from gravity- and gauge-mediated theories to hybrid models and models with flavor symmetries. Examples of measurements at LEP II, the LHC, and the NLC are given.

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arXiv1997

Determining $\tanβ$ at the NLC with SUSY Higgs Bosons

We examine the prospects for determining $\tanβ$ from heavy Higgs scalar production in the minimal supersymmetric standard model at a future $e^+e^-$ collider. Our analysis is independent of assumptions of parameter unification, and we consider general radiative corrections in the Higgs sector. Bounds are presented for $\sqrt{s} = 500$ GeV and 1 TeV, several Higgs masses, and a variety of integrated luminosities. For all cases considered, it is possible to distinguish low, moderate, and high $\tanβ$. In addition, we find stringent constraints for $3\lesssim\tanβ\lesssim 10$, and, for some scenarios, also interesting bounds on high $\tanβ$ through $tbH^{\pm}$ production. Such measurements may provide strong tests of the Yukawa unifications in grand unified theories and make possible highly precise determinations of soft SUSY breaking mass parameters.

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arXiv1997

Signatures of multi-TeV scale particles in supersymmetric theories

Supersymmetric particles at the multi-TeV scale will escape direct detection at planned future colliders. However, such particles induce non-decoupling corrections in processes involving the accessible superparticles through violations of the supersymmetric equivalence between gauge boson and gaugino couplings. In a previous study, we parametrized these violations in terms of super-oblique parameters and found significant deviations in well-motivated models. Here, we systematically classify the possible experimental probes of such deviations, and present detailed investigations of representative observables available at a future linear collider. In some scenarios, the $e^-e^-$ option and adjustable beam energy are exploited to achieve high precision. It is shown that precision measurements are possible for each of the three coupling relations, leading to significant bounds on the masses and properties of heavy superparticles and possible exotic sectors.

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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.

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arXiv1997

CP Violation from Slepton Oscillations at the LHC and NLC

In supersymmetric theories the charged sleptons of different generations may oscillate amongst themselves while they decay. In the case of three generation oscillations, superpartner production at the LHC and NLC may lead to an observable $CP$-violating signal $N(e^+μ^-) - N(μ^+e^-)$. This signal is proportional to a $CP$-violating invariant of the slepton mass matrix, $\widetilde{J}$, which is not constrained by searches for the electric dipole moment of the electron. The sensitivity of the LHC and NLC to this signal is highly dependent on superpartner masses, but $\widetilde{J}$ may be probed to a level of $10^{-3}$. Observation of the $CP$-violating signal would imply a definite structure for the slepton mass matrices and have strong implications for models of flavor and SUSY breaking.

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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.

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arXiv1996

Determining $tan β$ from the SUSY Higgs Sector at Future e^+e^- Colliders

We examine the prospects for determining $tan β$ from heavy Higgs scalar production in the minimal supersymmetric standard model at a future $e^+ e^-$ collider. Our analysis is independent of assumptions of parameter unification, and we consider general radiative corrections in the Higgs sector. Bounds are presented for $\sqrt{s} = 500$ GeV and 1 TeV, several Higgs masses, a variety of integrated luminosities and b-tagging efficiencies, and in scenarios with and without supersymmetric decays of the Higgs bosons. We find stringent constraints for $3 \alt tan β\alt 10$, and, for some scenarios, also interesting bounds on high $tan β$ through $tbH^{\pm}$ production. These bounds imply that simple Yukawa unifications may be confirmed or excluded. Implications for soft scalar mass determination and top squark parameters are also discussed.

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arXiv1996

Lepton Flavor Violation at LEP II and Beyond

If sleptons are produced at LEP II or the Next Linear Collider, lepton flavor violation can be probed at a level significantly below the current bounds from rare processes, such as $μ\to eγ$. Polarizable $e^-$ beams and the $e^-e^-$ mode at the NLC are found to be powerful options.

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arXiv1996

Measuring SUSY Parameters at LEP II Using Chargino Production and Decay

Previously, in the context of the minimal supersymmetric standard model (without {\em a priori} assumptions of parameter unification), we studied the constraints on weak-scale SUSY parameters from chargino production at LEP II, using as observables $\mch$, $\mLSP$, the cross section and the leptonic branching fraction. Here, exploiting the high degree of polarization in chargino production, we add to our earlier work the forward-backward asymmetries of the visible hadrons and leptons in chargino decays. For a chargino that is mostly gaugino, the parameter space can now be restricted to a small region; $\tanb$ is constrained, the soft electroweak gaugino and electron sneutrino masses are determined to about 10\%, and the sign of $μ$ may be determined. Constraints for a chargino that is mostly Higgsino are much weaker, but still disfavor the hypothesis that the chargino is mostly gaugino. For a chargino which is a roughly equal mixture of Higgsino and gaugino, we find intermediate results.

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arXiv1996

Extracting $R_b$ and $R_c$ Without Flavor Tagging

At present, two outstanding discrepancies between experiment and the standard model are the measurements of the hadronic branching fractions $R_b$ and $R_c$. We note that an independent measurement of these branching fractions may be obtained from the width of hadronic $Z$ decays with a prompt photon, $Γ_{qqγ}$, along with the total hadronic decay rate, $Γ_{had}$, and an additional theoretical assumption. Such an analysis requires no flavor tagging. We consider several plausible theoretical assumptions and find that the current value of $Γ_{qqγ}$ favors larger $R_b$ and smaller $R_c$ relative to standard model predictions, in accord with the direct measurements. If $Γ_{qqγ}$ and $Γ_{had}$ are combined with the direct measurements, generation-blind corrections to all up-type and all down-type quark widths are most favored. An updated measurement of $Γ_{qqγ}$ with the currently available LEP data is likely to provide an even stronger constraint on both the branching fraction discrepancies and their possible non-standard model sources.

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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.

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arXiv1994

Testing Supersymmetry at the Next Linear Collider

If new particles are discovered, it will be important to determine if they are the supersymmetric partners of standard model bosons and fermions. Supersymmetry predicts relations among the couplings and masses of these particles. We discuss the prospects for testing these relations at a future $e^+e^-$ linear collider with measurements that exploit the availability of polarized beams.

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arXiv1994

Determination of Fundamental Supersymmetry Parameters from Chargino Production at Lepii

If accessible at LEP II, chargino production is likely to be one of the few available supersymmetric signals for many years. We consider the prospects for the determination of fundamental supersymmetry parameters in such a scenario. The study is complicated by the dependence of observables on a large number of these parameters. We propose a straightforward procedure for disentangling these dependences and demonstrate its effectiveness by presenting a number of case studies at representative points in parameter space. Working in the context of the minimal supersymmetric standard model, we find that chargino production by itself is a fairly sensitive probe of the supersymmetry-breaking sector. For significant regions of parameter space, it is possible to test the gaugino mass unification hypothesis and to measure the gaugino contents of the charginos and neutralinos, thereby testing the predictions of grand unification and the viability of the lightest supersymmetric particle as a dark matter candidate. For much of the parameter space, it is also possible to set limits on the mass of the electron sneutrino, which provide a valuable guide for future particle searches.

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