Decays of W Bosons to Charginos and Neutralinos

The region of the supersymmetry parameter space, in which charginos decay predominantly into sneutrinos and leptons: chi+ -> \tilde{\nu} + l+, is not excluded experimentally for small mass differences between charginos and sneutrinos. The decay sneutrinos are invisible in R-parity conserving theories since they are either the lightest supersymmetric particles or they decay primarily into the channel: neutrino + lightest neutralino. If the energy of the decay leptons is so small that they escape detection, chargino events e+e- -> chi+chi- in e+e- collisions remain invisible, eroding the excluded chargino mass range at LEP. This region of the supersymmetry parameter space can partly be covered by searching for single W events in e+e- -> W+W-$, with one W boson decaying to leptons or quark jets, but the second W boson decaying to (undetected) charginos and neutralinos.Comment: 11 pages, 3 figures, uses epsfig.st

Universal Quantum Computation using Exchange Interactions and Teleportation of Single-Qubit Operations

We show how to construct a universal set of quantum logic gates using control over exchange interactions and single- and two-spin measurements only. Single-spin unitary operations are teleported instead of being executed directly, thus eliminating a major difficulty in the construction of several of the most promising proposals for solid-state quantum computation, such as spin-coupled quantum dots, donor-atom nuclear spins in silicon, and electrons on helium. Contrary to previous proposals dealing with this difficulty, our scheme requires no encoding redundancy. We also discuss an application to superconducting phase qubits.Comment: 4.5 pages, including 2 figure

Initial clinical experience with Myxo-ETlogix∗∗Myxo-ETlogix is a trade name of Edwards Lifesciences LLC, Irvine, Calif. mitral valve repair ring

ObjectiveComplexity of mitral valve repair for myxomatous disease has led to low adoption. We report initial experience with a new ring designed specifically for myxomatous disease, the Myxo-ETlogix (Edwards Lifesciences LLC, Irvine, Calif).MethodsFrom March 15, 2006, through November 19, 2007, 129 patients underwent mitral valve surgery for pure myxomatous disease, and 124 valves (96.1%) were repaired. The Myxo-ETlogix ring was used in 100 cases and the Physio ring (Edwards) in 24. The Myxo-ETlogix design includes a 3-dimensional shape to reduce systolic anterior motion and a larger orifice to accommodate elongated leaflets and decrease need for sliding plasty. Direct mitral valve measurements were made. Sizing was based on A2 height, and choice of ring type was based on unresected leaflet heights.ResultsThere was no operative mortality or lasting perioperative morbidity. The Myxo-ETlogix group had taller A2, P1, P2, and P3 leaflet segments than the Physio group (P ≤ .003). Only 1 sliding plasty was performed for asymmetry in the Myxo-ETlogix group. Predischarge and follow-up echocardiograms (n = 338 in 124 patients) disclosed transient nonobstructive chordal systolic anterior motion in 3 echocardiograms in 3 patients. No patients had 2+ or greater mitral regurgitation. At discharge, 5.7% had 1+ mitral regurgitation; this proportion was 17.3% at last follow-up (mean 6.1 ± 4.4 months).ConclusionIn initial experience with the Myxo-ETlogix ring, nonobstructive systolic anterior motion has been rare and obstructive systolic anterior motion not observed. Ongoing prospective echocardiographic and clinical studies will elucidate the role of this etiology-specific ring

Entanglement in quantum computers described by the XXZ model with defects

We investigate how to generate maximally entangled states in systems characterized by the Hamiltonian of the XXZ model with defects. Some proposed quantum computers are described by such model. We show how the defects can be used to obtain EPR states and W states when one or two excitations are considered.Comment: 4 pages, 1 figur

Encoded Universality for Generalized Anisotropic Exchange Hamiltonians

We derive an encoded universality representation for a generalized anisotropic exchange Hamiltonian that contains cross-product terms in addition to the usual two-particle exchange terms. The recently developed algebraic approach is used to show that the minimal universality-generating encodings of one logical qubit are based on three physical qubits. We show how to generate both single- and two-qubit operations on the logical qubits, using suitably timed conjugating operations derived from analysis of the commutator algebra. The timing of the operations is seen to be crucial in allowing simplification of the gate sequences for the generalized Hamiltonian to forms similar to that derived previously for the symmetric (XY) anisotropic exchange Hamiltonian. The total number of operations needed for a controlled-Z gate up to local transformations is five. A scalable architecture is proposed.Comment: 11 pages, 4 figure

Dynamical Decoupling Using Slow Pulses: Efficient Suppression of 1/f Noise

The application of dynamical decoupling pulses to a single qubit interacting with a linear harmonic oscillator bath with $1/f$ spectral density is studied, and compared to the Ohmic case. Decoupling pulses that are slower than the fastest bath time-scale are shown to drastically reduce the decoherence rate in the $1/f$ case. Contrary to conclusions drawn from previous studies, this shows that dynamical decoupling pulses do not always have to be ultra-fast. Our results explain a recent experiment in which dephasing due to $1/f$ charge noise affecting a charge qubit in a small superconducting electrode was successfully suppressed using spin-echo-type gate-voltage pulses.Comment: 5 pages, 3 figures. v2: Many changes and update

An observation of spin-valve effects in a semiconductor field effect transistor: a novel spintronic device

We present the first spintronic semiconductor field effect transistor. The injector and collector contacts of this device were made from magnetic permalloy thin films with different coercive fields so that they could be magnetized either parallel or antiparallel to each other in different applied magnetic fields. The conducting medium was a two dimensional electron gas (2DEG) formed in an AlSb/InAs quantum well. Data from this device suggest that its resistance is controlled by two different types of spin-valve effect: the first occurring at the ferromagnet-2DEG interfaces; and the second occuring in direct propagation between contacts.Comment: 4 pages, 2 figure

Higgs boson mass limits in perturbative unification theories

Motivated in part by recent demonstrations that electroweak unification into a simple group may occur at a low scale, we detail the requirements on the Higgs mass if the unification is to be perturbative. We do this for the Standard Model effective theory, minimal supersymmetry, and next-to-minimal supersymmetry with an additional singlet field. Within the Standard Model framework, we find that perturbative unification with sin2(thetaW)=1/4 occurs at Lambda=3.8 TeV and requires mh<460 GeV, whereas perturbative unification with sin2(thetaW)=3/8 requires mh<200 GeV. In supersymmetry, the presentation of the Higgs mass predictions can be significantly simplified, yet remain meaningful, by using a single supersymmetry breaking parameter Delta_S. We present Higgs mass limits in terms of Delta_S for the minimal supersymmetric model and the next-to-minimal supersymmetric model. We show that in next-to-minimal supersymmetry, the Higgs mass upper limit can be as large as 500 GeV even for moderate supersymmetry masses if the perturbative unification scale is low (e.g., Lambda=10 TeV).Comment: 20 pages, latex, 6 figures, references adde

Freedom in Nature

The paper starts with the proposal that the cause of the apparent insolubility of the free-will problem are several popular but strongly metaphysical notions and hypotheses. To reduce the metaphysics, some ideas are borrowed from physics. A concept of event causality is discussed. The importance of Hume's Principle of Causality is stressed and his Principle of Causation is weakened. The key concept of the paper, the so-called relative freedom, is also suggested by physics. It is a kind of freedom that can be observed everywhere in nature. Turning to biology, incomplete knowledge is defined for all organisms. They cope with the problem by Popper's trial and error processes. One source of their success is the relative freedom of choice from the basic option ranges: mutations, motions and neural connections. Finally, the conjecture is adopted that communicability can be used as a criterion of consciousness and free will is defined as a conscious version of relative freedom. The resulting notion is logically self-consistent and it describes an observable phenomenon that agrees with our experience.Comment: Changes: Improved formulation, three references added; 22 pages, no figure. Comments are welcom

Color-Octet Scalars of N=2 Supersymmetry at the LHC

The color gauge hyper-multiplet in N=2 supersymmetry consists of the usual N=1 gauge vector/gaugino super-multiplet, joined with a novel gaugino/scalar super-multiplet. Large cross sections are predicted for the production of pairs of the color-octet scalars $\sigma$ [sgluons] at the LHC: $gg, q\bar{q} \to \sigma\sigma^{\ast}$. Single $\sigma$ production is possible at one-loop level, but the $g g\to \sigma$ amplitude vanishes in the limit of degenerate $L$ and $R$ squarks. When kinematically allowed, $\sigma$ decays predominantly into two gluinos, whose cascade decays give rise to a burst of eight or more jets together with four LSP's as signature for $\sigma$ pair events at the LHC. $\sigma$ can also decay into a squark-antisquark pair at tree level. At one-loop level $\sigma$ decays into gluons or a $t \bar t$ pair are predicted, generating exciting resonance signatures in the final states. The corresponding partial widths are very roughly comparable to that for three body final states mediated by one virtual squark at tree level.Comment: LaTeX, 12 pages, 5 embedded figures. Added a couple of references; version to appear in Phys. Lett.