Search Results (11 total)

We propose a new framework for understanding the hierarchies of fermion masses and mixings. The masses and mixings of all standard model (SM) charged fermions other than top arise from higher dimensional operators involving a messenger scalar S and flavon scalars F_i. The flavons spontaneously break SM flavor symmetries at around the TeV scale. The SM singlet scalar S couples directly to the Higgs H and spontaneously breaks another U(1) at the electroweak scale. At the TeV scale, SM quarks and charged leptons have renormalizable couplings to S, but not to H or F_i. These couplings involve new heavy vectorlike fermions. Integrating out these fermions produces a pattern of higher dimensional operators that reproduce the observed hierarchies of the SM masses and mixings in terms of powers of the “little hierarchy”: the ratio of the electroweak scale to the flavor-breaking scale. The framework has important phenomenological implications. Flavor-changing neutral currents are within experimental limits but D⁰-D̅ ⁰ mixing and B_s→μ⁺μ^- could be close to current sensitivities. The neutral scalar s of the messenger field mixes with the light Higgs of the SM, which can have strong effects on Higgs decay branching fractions. The s mass eigenstate may be lighter than the Higgs, and could be detected at the Tevatron or the LHC.

We present some phenomenology of a new class of intersecting D-brane models. Soft supersymmetry (SUSY) breaking terms for these models are calculated in the u-moduli dominant SUSY breaking approach (in type IIA). In this case, the dependence of the soft terms on the Yukawas and Wilson lines drops out. These soft terms have a different pattern compared to the usual heterotic string models. Phenomenological implications for dark matter are discussed.

We estimate the Fermilab Tevatron run II potential for top and bottom squark searches. We find an impressive reach in several of the possible discovery channels. We also study some new channels which may arise in nonconventional supersymmetry models. In each case we rely on a detailed Monte Carlo simulation of the collider events and the CDF detector performance in run I.

We study the supersymmetry reach of the Fermilab Tevatron in channels containing both isolated leptons and identified tau jets. In the most challenging case, where the branching ratios of gauginos to taus dominate, we find that searches for two leptons, a tau jet and a large amount of missing transverse energy have a much better reach than the classic trilepton signature. With a total integrated luminosity of L≳4fb^-1, the Tevatron will start extending the expected CERN LEP-II reach for supersymmetry.

The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides work on the parameters of a 3–4 and 0.5 TeV center-of-mass (COM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (COM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay (π→μν_μ) channel, muon cooling, acceleration, storage in a collider ring, and the collider detector. We also present theoretical and experimental R&D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the research and development since the feasibility study of muon colliders presented at the Snowmass '96 Workshop [R. B. Palmer, A. Sessler, and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].

We consider the novel Kaluza-Klein (KK) scenario where gravity propagates in the (4+n)-dimensional bulk of spacetime, while gauge and matter fields are confined to the (3+1)-dimensional world volume of a brane configuration. For simplicity we assume compactification of the extra n dimensions on a torus with a common scale R, and identify the massive KK states in the four-dimensional spacetime. For a given KK level n→ there is one spin-2 state, (n-1) spin-1 states, and n(n-1)/2 spin-0 states, all mass degenerate. We construct the effective interactions between these KK states and ordinary matter fields (fermions, gauge bosons, and scalars). We find that the spin-1 states decouple and that the spin-0 states only couple through the dilaton mode. We then derive the interacting Lagrangian for the KK states and standard model fields, and present the complete Feynman rules. We discuss some low-energy phenomenology for these new interactions for the case when 1/R is small compared to the electroweak scale, and the ultraviolet cutoff of the effective KK theory is on the order of 1 TeV.

Recent developments in string duality suggest that the string scale may not be irrevocably tied to the Planck scale. Two explicit but unrealistic examples are described where the ratio of the string scale to the Planck scale is arbitrarily small. Solutions that are more realistic may exist in the intermediate coupling or "truly strong coupling" region of the heterotic string. Weak scale superstrings have dramatic experimental consequences for both collider physics and cosmology.

We explore the possibility of unification of gauge couplings near the Planck scale in models of extended technicolor. We observe that models of the form G×SU(3)_c×SU(2)_L×U(1)_Y cannot be realized, due to the presence of massless neutral Goldstone bosons (axions) and light charged pseudo Goldstone bosons; thus, unification of the known forces near the Planck scale cannot be achieved. The next simplest possibility, G×SU(4)_PS×SU(2)_L×U(1)_T3R, cannot lead to unification of the Pati-Salam and weak gauge groups near the Planck scale. However, superstring theory provides relations between couplings at the Planck scale without the need for an underlying grand-unified gauge group, which allows unification of the SU(4)_PS and SU(2)_L couplings.

The renormalized Chern-Simons term at finite density is shown to vanish when the renormalized coefficient at zero density takes values Ne² / 2π. Thus in the Chern-Simons description a system of anyons at zero temperature is a superfluid. This result is shown to hold to all orders in perturbation theory by generalizing a nonrenormalization theorem of the zero-density case. We also discuss the finite-temperature case, where a perturbative Chern-Simons mass appears.

A large-N matrix model with fermions is considered in a gauge-invariant formalism. In large N the model contains "baryons." The baryon wave functions and masses are computed explicitly to leading order in N. Higher-order corrections are also considered. The baryon wave functions are of the WKB type. The WKB "potential" is shown to be linear for strong coupling, Coulomb-type for weak coupling.

The possibility of the charge-monopole systems with half-integer spin in the grand unified SU(5) model is investigated and found to occur.