Search Results (42 total)

The properties of quantum mechanics with a discrete phase space are studied. The minimum uncertainty states are found and these states become the Gaussian wave packets in the continuum limit. With a suitably chosen Hamiltonian that gives free particle motion in the continuum limit, it is found that full or approximate periodic time evolution can result. This represents an example of revivals of wave packets that in the continuum limit is the familiar free particle motion on a line. Finally we examine the uncertainty principle for discrete phase space and obtain the correction terms to the continuum case.

Interacting dark energy and the holographic principle offer a possible way of addressing the cosmic coincidence problem as well as accounting for the size of the dark energy component. The equilibrium points of the Friedmann equations which govern the evolution behavior of dark energy, matter, and curvature components can determine the qualitative behavior of the cosmological models. These possible equilibria and their behavior are examined in a general framework, and some illustrative examples are presented.

The generalized uncertainty principle has been described as a general consequence of incorporating a minimal length from a theory of quantum gravity. We consider a simple quantum mechanical model where the operator corresponding to position has discrete eigenvalues and show how the generalized uncertainty principle results for minimum uncertainty wave packets.

Heavy singlet neutrinos admit Majorana masses which are not possible for the Standard Model particles. This suggest new possibilities for generating the masses and mixing angles of light neutrinos. We present a model of neutrino physics which combines the source of lepton-number violation with the flavor symmetry responsible for the hierarchy in the charged lepton and quark sector. This is accomplished by giving the scalar field effecting the lepton-number violation a nonzero charge under the horizontal flavor symmetry. We find an economical model which is consistent with the measured values of the atmospheric and solar neutrino mass-squares and mixing angles.

We explore a model of interacting dark energy where the dark energy density is related by the holographic principle to the Hubble parameter, and the decay of the dark energy into matter occurs at a rate comparable to the current value of the Hubble parameter. We find this gives a good fit to the observational data supporting an accelerating Universe, and the model represents a possible alternative interpretation of the expansion history of the Universe.

The introduction of an interaction for dark energy to the standard cosmology offers a potential solution to the cosmic coincidence problem. We examine the conditions on the dark energy density that must be satisfied for this scenario to be realized. Under some general conditions we find a stable attractor for the evolution of the Universe in the future. Holographic conjectures for the dark energy offer some specific examples of models with the desired properties.

We investigate the sensitivity of future photon-photon colliders to low scale gravity scenarios via the process γγ→ZZ where the Kaluza-Klein boson exchange contributes only when the initial state photons have opposite helicity. We contrast this with the situation for the process γγ→γγ where the t and u channels also contribute. We include the one-loop standard model background whose interference with the graviton exchange determines the experimental reach in measuring any deviation from the standard model expectations and explore how polarization can be exploited to enhance the signal over background. We find that a 1 TeV linear collider has an experimental reach to mass scale of about 4 TeV in this channel.

Synchronization measures have become an important tool for exploring the relationships between time series. We review three recently proposed nonlinear synchronization measures and expand their definitions in a straightforward way to apply to an ensemble of measurements. We also develop a synchronization measure in which nearest neighbors are determined across the ensemble. We compare these four nonlinear synchronization measures and show that our measure succeeds in physically motivated examples where the other methods fail. We apply the synchronization measure to human electrocorticogram data collected during an auditory event-related potential experiment. The results suggest a crude model of cortical connectivity.

Superfield realizations of Lorentz-violating extensions of the Wess-Zumino model are presented. These models retain supersymmetry but include terms that explicitly break the Lorentz symmetry. The models can be understood as arising from superspace transformations that are modifications of the familiar one in the Lorentz-symmetric case.

We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs factories and compact high-energy lepton colliders. The status and time scale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons.

Supersymmetric field theories can be constructed that violate Lorentz and CPT symmetry. We illustrate this with some simple examples related to the original Wess-Zumino model.

We relate leptogenesis in a class of theories to low-energy experimental observables: quark and lepton masses and mixings. With reasonable assumptions motivated by grand unification, one can show that the CP-asymmetry parameter takes a universal form. Furthermore the dilution mass is related to the light neutrino masses. Overall, these models offer an explanation for a lepton asymmetry in the early universe.

Higgs boson mass sum rules of supersymmetric models offer attractive targets for precision tests at future muon colliders. These sum rules involve the gauge boson masses as well as the masses of the Higgs boson states which can be precisely measured in the s-channel production process at a muon collider. These measurements can sensitively probe radiative corrections to the Higgs boson masses as well as test for CP violation and nonminimality of the Higgs sector.

We show how introducing discrete Abelian flavor symmetries can produce texture zeros in the fermion mass matrices, while preserving the correct relationships with the low-energy data on quark and lepton masses. We outline a procedure for defining texture zeros as suppressed entries in Yukawa matrices. These texture zeros can account for the coexistence of the observed large mixing in atmospheric neutrino oscillations with a hierarchy in the neutrino masses, and offer the possibility of alignment of the quark and squark mass matrices, thus giving a solution to the supersymmetric flavor problem. A requirement that the flavor symmetry commutes with the SU(5) grand unified group can be used to explain the lepton mass hierarchies as well as the neutrino parameters, including the large mixing observed in the atmospheric neutrino data. We present one such model that yields a large atmospheric neutrino mixing angle, as well as a solar neutrino mixing angle of order λ≃0.22.

We show that one can describe the quark and lepton masses with a single anomaly-free U(1) flavor symmetry provided a single order one parameter is enhanced by roughly 4–5. The flavor symmetry can be seen to arise from inside the E₆ symmetry group in such a way that it commutes with the SU(5) grand unified gauge group. The scenario does not distinguish between the left-handed lepton doublets and hence is a model of neutrino anarchy. It can therefore account for the large mixing observed in atmospheric neutrino experiments and predicts that the solar neutrino oscillation data are consistent with the large mixing angle solution of matter-enhanced oscillations.

We show that solutions for the masses and mixings of the quarks and leptons based on a U(1)×Z₂ horizontal symmetry are possible. The seesaw mechanism is shown to work consistently in the presence of the discrete symmetry. The discrete symmetry results in the phenomenologically useful suppressions of elements of the Yukawa matrices. The quark and lepton masses, the CKM mixing angles, and the neutrino mixing angles are accommodated at the order of magnitude level.

We study the impact of a set of horizontal symmetries on the requirements for producing the baryon asymmetry of the universe via leptogenesis. We find that Abelian horizontal symmetries lead to a simple description of the parameters describing leptogenesis in terms of the small expansion parameter that arises from spontaneous symmetry breaking. If the family symmetry is made discrete, then an enhancement in the amount of leptogenesis can result.

We study a set of textures giving rise to the correct masses and mixings of the charged fermions in the context of leptogenesis. The Dirac neutrino texture pattern is assumed to be identical with the up quark texture. The heavy Majorana neutrino mass matrix is obtained by inverting the type-I seesaw formula and using the neutrino masses and mixings required by the solar and atmospheric neutrino oscillation experiments as input. After making a feasibility study of the generated lepton asymmetry via the decay of the heavy right handed neutrino, we compute the generated baryon asymmetry by numerically solving the supersymmetric Boltzmann equations. We find for these models that both the hierarchy of the texture as well as the placement of the texture zeros are important to the viability of leptogenesis as the source of the observed baryon asymmetry of the universe.

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 analyze the prospects at a muon collider for measuring chargino masses in the μ⁺μ^-→χ̃⁺χ̃^- process in the threshold region. We find that for a gaugino-like chargino of mass 100–200 GeV, a measurement better than 50–300 MeV should be possible with 50 fb^-1 integrated luminosity. The accuracy obtained here is better than with other techniques or at other facilities. The muon sneutrino mass, which enters through the ν̃_μ exchange diagram, can also be simultaneously measured to a few GeV if it is not too heavy.

We present the full one-loop calculation for gg→ZZ in the minimal supersymmetric standard model (MSSM) including nonresonant contributions from the squark loop diagrams and provide analytical expressions for the helicity amplitudes. The one-loop process gg→ZZ via quark loops has been calculated in the standard model. In supersymmetric models, additional contributions arise from squark loops. In some regions of the MSSM parameter space, the top and bottom squark loops can make important contributions to the diagrams involving Higgs bosons. The heavy Higgs scalar (H) might be detected at the CERN Large Hadron Collider via gg→H→ZZ for tan β≲5.

Precise determinations of the masses of the W boson and of the top quark could stringently test the radiative structure of the standard model (SM) or provide evidence for new physics. We analyze the excellent prospects at a muon collider for measuring M_W and m_t in the W⁺W^- and tt̅ threshold regions. With an integrated luminosity of 10 (100) fb^-1, the W-boson mass could be measured to a precision of 20 (6) MeV, and the top-quark mass to a precision of 200 (70) MeV, provided that theoretical and experimental systematics are understood. A measurement of Δm_t=200 MeV for fixed M_W would constrain a 100 GeV SM Higgs boson mass within about ±2 GeV, while ΔM_W=6 MeV for fixed m_t would constrain m_h to about ±10 GeV.

We demonstrate that a measurement at future colliders of the Bjorken process e⁺e^-, μ⁺μ^-→ZH in the threshold region can yield a precise determination of the Higgs boson mass. With an integrated luminosity of 100 fb^-1 it is possible to measure the standard model Higgs mass to within 45 MeV (60 MeV) at μ⁺μ^- (e⁺e^-) collider for m_H  =  100 GeV.

We discuss the excellent prospects for a detailed study of a strongly interacting electroweak sector at a muon collider with a c.m. energy sqrt[s]∼4 TeV. For an expected luminosity of L=200–1000 fb^-1 per year, μ⁺μ^- and μ⁺μ⁺ (or μ^-μ^-) collisions can be used to study longitudinal W⁺W^- and W⁺W⁺ (or W^-W^-) scattering with considerable precision. In particular, detailed measurements of the distribution in the VV pair masses (V=W^±,Z) will be possible. The shape and magnitude of these distributions will provide a powerful tool for determining the nature of strong gauge-boson interactions. Event rates will be large enough that projection techniques can be used to directly isolate final states with different polarizations of the V’s and verify that the strong interaction cross section excess is mainly in the longitudinal-longitudinal mode.

We study the evolution of R-parity-violating (RPV) couplings in the minimum supersymmetric standard model, between the electroweak and grand unification scales, assuming a family hierarchy for these coupling strengths. Particular attention is given to solutions where both the R-conserving and R-violating top-quark Yukawa couplings simultaneously approach infrared fixed points; these we analyze both algebraically and with numerical solutions of the evolution equations at the one-loop level. We identify constraints on these couplings at the GUT scale, arising from lower limits on the top-quark mass. We show that fixed points offer a new source of bounds on RPV couplings at the electroweak scale. We derive evolution equations for the CKM matrix, and show that RPV couplings affect the scaling of the unitarity triangle. The fixed-point behavior is compatible with all present experimental constraints. However, fixed-point values of RPV top-quark couplings would require the corresponding sleptons or squarks to have a mass ≳m_t to suppress strong new top-quark decays to sparticles.