arXiv subjects

Scott Thomas

Publications and source records attributed to Scott Thomas.

At least 55 records · Page 3Linked to original sources

arXiv1998

Massive Doublet Leptons

Massive vector-like electroweak doublets are generic in many extensions of the standard model. Even though one member of the doublet is necessarily electrically charged these particles are not easily detected in collider experiments. The neutral and charged states within the doublet are split by electroweak symmetry breaking. In the absence of mixing with other states, the radiatively generated splitting is in the range 200 - 350 MeV for m > mZ/2. The charged state decays to the neutral one with an O(cm) decay length, predominantly by emission of a soft charged pion. The best possibility to detect these massive charged particles is to trigger on hard initial state radiation and search for two associated soft charged pions with displaced vertices. The mass reach for this process at LEPII is limited by luminosity rather than kinematics.

hep-ph↗

arXiv1998

CP-odd Phases in Slepton Pair Production

The effects of CP-odd supersymmetric phases on slepton pair production are considered. It is shown that CP-even observables in $e^+ e^-$ and $e^- e^-$ collisions, such as the total selectron cross section, can depend on CP-odd supersymmetric phases through interference between different tree level amplitudes. Left handed selectron pair production in $e^- e^-$ collisions is particularly sensitive to the relative phase between the bino and wino masses. This sensitivity is not limited to any kinematic regime and extends over all of neutralino parameter space. The relative phase between the bino and wino masses is a renormalization group invariant at one-loop, and as such provides a clean probe for operators which violate gaugino universality at the messenger scale.

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arXiv1998

Recent Developments in Dynamical Supersymmetry Breaking

Some formal aspects of supersymmetry breaking are reviewed. The classic "requirements" for supersymmetry breaking include chiral matter, a dynamical superpotential, and a classical superpotential which completely lifts the moduli space. These "requirements" may be evaded in theories with large matter representations. The mechanisms of supersymmetry breaking by confinement and quantum deformation of the moduli space are explained, with emphasis on the importance of identifying the relevant degrees of freedom in the ground state. Supersymmetry breaking and the behavior of the Witten index in non-chiral theories are discussed. The quantum removal of directions which are classically unlifted is also illustrated. Examples of product gauge group theories that admit dual descriptions of the non-supersymmetric ground state are also presented.

hep-th↗

arXiv1996

Sparticle Spectroscopy and Electroweak Symmetry Breaking with Gauge-Mediated Supersymmetry Breaking

The phenomenology associated with gauge-mediated supersymmetry breaking is presented. A renormalization group analysis of the minimal model is performed in which the constraints of radiative electroweak symmetry breaking are imposed. The resulting superpartner and Higgs boson spectra are highly correlated and depend on only a few parameters. Superpartner mass ratios and sum rules are identified which can be tested at future colliders. Some of these relations are logarithmically sensitive to the messenger scale, while others allow gauge-mediation to be distinguished from other schemes for tansmitting supersymmetry breaking. Deviations from the minimal model, such as larger messenger representations and additional contributions to Higgs sector masses, can in some circumstances dramatically modify the low energy spectrum. These modifications include a slepton or Higgsino as the lightest standard model superpartner, or exotic mass relations among the scalars and gauginos. The contribution to $b \to s γ$ and resulting bound on superpartner masses are also presented for the minimal model. Finally, the unique collider signatures of heavy charged particle production, or decay to the Goldstino within a detector are discussed.

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arXiv1996

Dual Descriptions of Supersymmetry Breaking

Dynamical supersymmetry breaking is considered in models which admit descriptions in terms of electric, confined, or magnetic degrees of freedom in various limits. In this way, a variety of seemingly different theories which break supersymmetry are actually inter-related by confinement or duality. Specific examples are given in which there are two dual descriptions of the supersymmetry breaking ground state.

hep-th↗

arXiv1996

Phenomenological Implications of Low Energy Supersymmetry Breaking

The experimental signatures for low energy supersymmetry breaking are presented. The lightest standard model superpartner is unstable and decays to its partner plus a Goldstino, $G$. For a supersymmetry breaking scale below a few 1000 TeV this decay can take place within a detector, leading to very distinctive signatures. If a neutralino is the lightest standard model superpartner it decays by $χ_1^0 \to γ+ G$, and if kinematically accessible by $χ_1^0 \to (Z^0, h^0, H^0, A^0) + G$. These decays can give rise to displaced vertices. Alternately, if a slepton is the lightest standard model superpartner it decays by $\tilde{l} \to l + G$. This can be seen as a greater than minimum ionizing charged particle track, possibly with a kink to a minimum ionizing track.

hep-ph↗

arXiv1996

Implications of Low Energy Supersymmetry Breaking at the Tevatron

The signatures for low energy supersymmetry breaking at the Tevatron are investigated. It is natural that the lightest standard model superpartner is an electroweak neutralino, which decays to an essentially massless Goldstino and photon, possibly within the detector. In the simplest models of gauge-mediated supersymmetry breaking, the production of right-handed sleptons, neutralinos, and charginos leads to a pair of hard photons accompanied by leptons and/or jets with missing transverse energy. The relatively hard leptons and softer photons of the single $e^+e^- γγ+ \EmissT$ event observed by CDF implies this event is best interpreted as arising from left-handed slepton pair production. In this case the rates for $l^{\pm} γγ+ \EmissT$ and $ γγ+ \EmissT$ are comparable to that for $l^+l^- γγ+ \EmissT$.

hep-ph↗

arXiv1996

Experimental Signatures of Low Energy Gauge Mediated Supersymmetry Breaking

The experimental signatures for gauge mediated supersymmetry breaking are presented. The phenomenology associated with this class of models is distinctive since the gravitino is naturally the LSP. The next lightest supersymmetric particle (NLSP) can be a gaugino, Higgsino, or right handed slepton. Decay of the NLSP to its partner plus the LSP proceeds through the Goldstino component of the gravitino. For a significant range of parameters this decay can take place within the detector, and can be measured as a displaced vertex or kink in a charged particle track. In the case that the NLSP is mostly gaugino, we identify the discovery modes as $e^+e^- \rightarrow γγ+ \Emiss$, and $p \bar{p} \rightarrow l^+ l^- γγ+ \EmissT$. If the NLSP is a right handed slepton the discovery modes are $e^+ e^- \rightarrow l^+ l^- + \Emiss$ and $p \bar{p} \rightarrow l^+ l^- + \EmissT$. An NLSP which is mostly Higgsino is also considered. Finally, these theories can contain scalar particles which mediate sub-millimeter range coherent forces of gravitational strength.

hep-ph↗

arXiv1996

Dynamical Supersymmetry Breaking on Quantum Moduli Spaces

Supersymmetry breaking by the quantum deformation of a classical moduli space is considered. A simple, non-chiral, renormalizable model is presented to illustrate this mechanism. The well known, chiral, $SU(3) \times SU(2)$ model and its generalizations are shown to break supersymmetry by this mechanism in the limit $Λ_2 \gg Λ_3$. Other supersymmetry breaking models, with classical flat directions that are only lifted quantum mechanically, are presented. Finally, by integrating in vector matter, the strongly coupled region of chiral models with a dynamically generated superpotential is shown to be continuously connected to a weakly coupled description in terms of confined degrees of freedom, with supersymmetry broken at tree level.

hep-th↗

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

Dynamical Relaxation of the Supersymmetric CP Violating Phases

A supersymmetric generalization of the Peccei-Quinn mechanism is proposed in which two U(1) CP violating phases of the supersymmetric standard model are promoted to dynamical variables. This amounts to postulating the existence of spontaneously broken global symmetries in the supersymmetry breaking sector. The vacuum can then relax near a CP conserving point. As a consequence the strong CP and supersymmetric CP problems may be solved by similar mechanisms.

hep-ph↗

arXiv1995

Baryogenesis from Flat Directions of the Supersymmetric Standard Model

Baryogenesis from the coherent production of a scalar condensate along a flat direction of the supersymmetric extension of the standard model (Affleck-Dine mechanism) is investigated. Two important effects are emphasized. First, nonrenormalizable terms in the superpotential can lift standard model flat directions at large field values. Second, the finite energy density in the early universe induces soft potentials with curvature of order the Hubble constant. Both these have important implications for baryogenesis, which requires large squark or slepton expectation values to develop along flat directions. In particular, the induced mass squared must be negative. The resulting baryon to entropy ratio is very insensitive to the details of the couplings and initial conditions, but depends on the dimension of the nonrenormalizable operator in the superpotential which stabilizes the flat direction and the reheat temperature after inflation. Unlike the original scenario, an acceptable baryon asymmetry can result without subsequent entropy releases. In the simplest scenario the baryon asymmetry is generated along the $LH_u$ flat direction, and is related to the mass of the lightest neutrino.

hep-ph↗

arXiv1995

Supersymmetry in the Very Early Universe

Supersymmetric flat directions can have a number of important consequences in the very early universe. Depending on the form of the SUSY breaking potential arising from the finite energy density at early times, coherent production of scalar condensates can result along such directions. This leads a cosmological disaster for Polonyi type flat directions with only Planck suppressed couplings, but can give rise to the baryon asymmetry for standard model flat directions. Flat directions are also natural candidates to act as inflatons. Achieving density fluctuations of the correct magnitude generally requires an additional hidden SUSY breaking sector.

hep-ph↗

arXiv1995

Moduli Inflation from Dynamical Supersymmetry Breaking

Moduli fields, which parameterize perturbative flat directions of the potential in supersymmetric theories, are natural candidates to act as inflatons. An inflationary potential on moduli space can result if the scale of dynamical SUSY breaking in some sector of the theory is determined by a moduli dependent coupling. The magnitude of density fluctuations generated during inflation then depends on the scale of SUSY breaking in this sector. This can naturally be hierarchically smaller than the Planck scale in a dynamical model, giving small fluctuations without any fine tuning of parameters. It is also natural for SUSY to be restored at the minimum of the moduli potential, and to leave the universe with zero cosmological constant after inflation. Acceptable reheating can also be achieved in this scenario.

hep-th↗

arXiv1995

Baryons and Dark Matter from the Late Decay of a Supersymmetric Condensate

The possibility that both the baryon asymmetry and dark matter arise from the late decay of a population of supersymmetric particles is considered. If the decay takes place below the LSP freeze out temperature, a nonthermal distribution of LSPs results. With conserved $R$ parity these relic LSPs contribute to the dark matter density. A net asymmetry can exist in the population of decaying particles if it arises from coherent production along a supersymmetric flat direction. The asymmetry is transferred to baryons if the condensate decays through the lowest order nonrenormalizable operators which couple to $R$ odd combinations of standard model particles. This also ensures at least one LSP per decay. The relic baryon and LSP number densities are then roughly equal. The ratio of baryon to dark matter densities is then naturally $\Omegab / \OmegaLSP \sim {\cal O}(\mb / \mLSP)$. The resulting upper limit on the LSP mass is model dependent but in the range ${\cal O}(30-140)$ GeV. The total relic density is related to the order at which the flat direction which gives rise to the condensate is lifted. The observed density is obtained for a direction which is lifted by a fourth order Planck scale suppressed operator in the superpotential.

hep-ph↗

arXiv1995

Supersymmetry Breaking in the Early Universe

Supersymmetry breaking in the early universe induces scalar soft potentials with curvature of order the Hubble constant. This has a dramatic effect on the coherent production of scalar fields along flat directions. For the moduli problem it generically gives a concrete realization of the problem by determining the field value subsequent to inflation. However it might suggest a solution if the minimum of the induced potential coincides with the true minimum. The induced Hubble scale mass also has important implications for the Affleck-Dine mechanism of baryogenesis. This mechanism requires large squark or slepton expectation values to develop along flat directions in the early universe. This is generally not the case if the induced mass squared is positive, but does occur if it is negative. The resulting baryon to entropy ratio depends mainly on the dimension of the nonrenormalizable operator in the superpotential which stabilizes the flat direction, and the reheat temperature after inflation. Unlike the original scenario, it is possible to obtain an acceptable baryon asymmetry without subsequent entropy releases.

hep-ph↗

arXiv1994

Solving the Cosmological Moduli Problem with Weak Scale Inflation

Many models of supersymmetry breaking involve particles with weak scale mass and Planck mass suppressed couplings. Coherent production of such particles in the early universe destroys the successful predictions of nucleosynthesis. We show that this problem may be solved by a brief period of weak scale inflation. Furthermore the inflaton potential for such an inflation naturally arises from the same assumptions which lead to the cosmological problem. Successful baryogenesis and preservation of density fluctuations for large scale structure formation are also possible in this scenario.

hep-ph↗

arXiv1994

Electromagnetic Contributions to the Schiff Moment

The Schiff moment, $\smij$, is a parity and time reversal violating fermion-fermion coupling. The nucleus-electron Schiff moment generically gives the most important contribution to the electric dipole moments of atoms and molecules with zero net intrinsic electronic spin and nuclear spin ${1 \over 2}$. Here, the electromagnetic contribution to the Schiff moment, $\emij$, is considered. For a nucleon, the leading chirally violating contribution to this interaction is calculable in the chiral limit in terms of the parity and time reversal violating pion-nucleon coupling. For the Schiff moment of heavy nuclei, this chiral contribution is somewhat smaller than the finite size effect discussed previously in the literature.

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