Disordered actomyosin networks are sufficient to produce cooperative and telescopic contractility

While the molecular interactions between individual myosin motors and F-actin are well established, the relationship between F-actin organization and actomyosin forces remains poorly understood. Here we explore the accumulation of myosin-induced stresses within a two-dimensional biomimetic model of the disordered actomyosin cytoskeleton, where myosin activity is controlled spatiotemporally using light. By controlling the geometry and the duration of myosin activation, we show that contraction of disordered actin networks is highly cooperative, telescopic with the activation size, and capable of generating non-uniform patterns of mechanical stress. We quantitatively reproduce these collective biomimetic properties using an isotropic active gel model of the actomyosin cytoskeleton, and explore the physical origins of telescopic contractility in disordered networks using agent-based simulations

Threshold Resummation Effects in the Associated Production of Chargino and Neutralino at Hadron Colliders

We investigate the QCD effects in the associated production of the chargino and the neutralino, $\tilde\chi^\pm_{1}$ and $\tilde\chi^0_{2}$, in the Minimal Supersymmetric Standard Model (MSSM) at both the Fermilab Tevatron and the CERN Large Hadron Collider (LHC). We include the next-to-leading order (NLO) QCD corrections (including supersymmetric QCD) and the threshold resummation effects. Our results show that, compared to the NLO predictions, the threshold resummation effects can increase the total cross sections by 3.6% and 3.9% for the associated production of $\tilde\chi^+_{1}\tilde\chi^0_{2}$ and $\tilde\chi^-_{1}\tilde\chi^0_{2}$ at the LHC, respectively, and by 4.7% for those of $\tilde\chi^\pm_{1}\tilde\chi^0_{2}$ at the Tevatron. In the invariant mass distributions the resummation effects are significant for large invariant mass. The threshold resummation reduces the dependence of the total cross sections at the LHC (Tevatron) on the renormalization/factorization scales to 5% (4%) from up to 7% (11%) at NLO.Comment: revised version with midifications, several references adde

Limiting Behaviour of the Mean Residual Life

In survival or reliability studies, the mean residual life or life expectancy is an important characteristic of the model. Here, we study the limiting behaviour of the mean residual life, and derive an asymptotic expansion which can be used to obtain a good approximation for large values of the time variable. The asymptotic expansion is valid for a quite general class of failure rate distributions--perhaps the largest class that can be expected given that the terms depend only on the failure rate and its derivatives.Comment: 19 page

Supersymmetric Electroweak Corrections to Single Top Quark Production at the Fermilab Tevatron

We have calculated the $O(\alpha_{ew} M_t^2/M_W^2)$ supersymmetric electroweak corrections to single top quark production via $q\bar q' \to t\bar b$ at the Fermilab Tevatron in the minimal supersymmetric model. The supersymmetric electroweak corrections to the cross section are a few percent for $tan \beta> 1$, and can exceed 10% for $tan\beta<1$. The combined effects of SUSY electroweak corrections and the Yukawa corrections can exceed 10% for favorable parameter values, which might be observable at a high-luminosity Tevatron.Comment: 13 pages, 4 figures available at reques

Limits on scalar leptoquark interactions and consequences for GUTs

A colored weak singlet scalar state with hypercharge 4/3 is one of the possible candidates for the explanation of the unexpectedly large forward-backward asymmetry in t tbar production as measured by the CDF and D0 experiments. We investigate the role of this state in a plethora of flavor changing neutral current processes and precision observables of down-quarks and charged leptons. Our analysis includes tree- and loop-level mediated observables in the K and B systems, the charged lepton sector, as well as the Z to b bbar decay width. We perform a global fit of the relevant scalar couplings. This approach can explain the (g-2)_mu anomaly while tensions among the CP violating observables in the quark sector, most notably the nonstandard CP phase (and width difference) in the Bs system cannot be fully relaxed. The results are interpreted in a class of grand unified models which allow for a light colored scalar with a mass below 1TeV. We find that the renormalizable SU(5) scenario is not compatible with our global fit, while in the SO(10) case the viability requires the presence of both the 126- and 120-dimensional representations.Comment: 26 pages, 7 figures; version as publishe

Quantitative Characterization of the T Cell Receptor Repertoire of Naive and Memory subsets Using an Integrated experimental and Computational Pipeline Which Is Robust, economical, and Versatile

The T cell receptor (TCR) repertoire can provide a personalized biomarker for infectious and non-infectious diseases. We describe a protocol for amplifying, sequencing, and analyzing TCRs which is robust, sensitive, and versatile. The key experimental step is ligation of a single-stranded oligonucleotide to the 3′ end of the TCR cDNA. This allows amplification of all possible rearrangements using a single set of primers per locus. It also introduces a unique molecular identifier to label each starting cDNA molecule. This molecular identifier is used to correct for sequence errors and for effects of differential PCR amplification efficiency, thus producing more accurate measures of the true TCR frequency within the sample. This integrated experimental and computational pipeline is applied to the analysis of human memory and naive subpopulations, and results in consistent measures of diversity and inequality. After error correction, the distribution of TCR sequence abundance in all subpopulations followed a power law over a wide range of values. The power law exponent differed between naïve and memory populations, but was consistent between individuals. The integrated experimental and analysis pipeline we describe is appropriate to studies of T cell responses in a broad range of physiological and pathological contexts

Polarized Single Top Production at Leptonic Colliders from Broken R Parity Interactions Incorporating CP Violation

The contribution from the R parity violating interactions in the associated production of a top quark with a charm antiquark is examined for high energy leptonic colliders. We concentrate on the reactions associated with the semileptonic top decay. A set of characteristic dynamical distributions for the signal events is evaluated and the results contrasted against those from the standard model W-boson pair production background. Next, we turn to a study of a CP-odd observable, associated with the top spin, which leads to an asymmetry in the energy distribution of the emitted charged leptons for the pair of CP-conjugate final states, $b \bar l \nu \bar c$ and $\bar b l \bar \nu c$. A non vanishing asymmetry arises from a CP-odd phase, embedded in the R parity violating coupling constants, through interference terms between the R parity violating amplitudes at both the tree and loop levels.Comment: revtex file. 17 pages. 7 postscript figures. 1 table. The revised version includes an estimate of experimental uncertainties. Submitted to Phys. Rev.

Single top quark production as a probe of R-parity-violating SUSY at pp and p\bar p colliders

We investigate the ability of single top quark production via qq'-> squark->tb and q \bar q'->slepton->t\bar b at the LHC and Tevatron to probe the strength of R-parity violating couplings in the minimal supersymmetric model. We found that given the existing bounds on R-parity violating couplings, single top quark production may be greatly enhanced over that predicted by the standard model, and that both colliders can either discover R-parity violating SUSY or set strong constraints on the relevant R-parity violating couplings. We further found that the LHC is much more powerful than the Tevatron in probing the squark couplings, but the two colliders have comparable sensitivity for the slepton couplings.Comment: 15 pages, 4 figure

Can Doubly Strange Dibaryon Resonances be Discovered at RHIC?

The baryon-baryon continuum invariant mass spectrum generated from relativistic nucleus + nucleus collision data may reveal the existence of doubly-strange dibaryons not stable against strong decay if they lie within a few MeV of threshold. Furthermore, since the dominant component of these states is a superposition of two color-octet clusters which can be produced intermediately in a color-deconfined quark-gluon plasma (QGP), an enhanced production of dibaryon resonances could be a signal of QGP formation. A total of eight, doubly-strange dibaryon states are considered for experimental search using the STAR detector (Solenoidal Tracker at RHIC) at the new Relativistic Heavy Ion Collider (RHIC). These states may decay to Lambda-Lambda and/or proton-Cascade-minus, depending on the resonance energy. STAR's large acceptance, precision tracking and vertex reconstruction capabilities, and large data volume capacity, make it an ideal instrument to use for such a search. Detector performance and analysis sensitivity are studied as a function of resonance production rate and width for one particular dibaryon which can directly strong decay to proton-Cascade-minus but not Lambda-Lambda. Results indicate that such resonances may be discovered using STAR if the resonance production rates are comparable to coalescence model predictions for dibaryon bound states.Comment: 28 pages, 5 figures, revised versio

Single Top Production as a Window to Physics Beyond the Standard Model

Production of single top quarks at a high energy hadron collider is studied as a means to identify physics beyond the standard model related to the electroweak symmetry breaking. The sensitivity of the $s$-channel $W^*$ mode, the $t$-channel $W$-gluon fusion mode, and the \tw mode to various possible forms of new physics is assessed, and it is found that the three modes are sensitive to different forms of new physics, indicating that they provide complimentary information about the properties of the top quark. Polarization observables are also considered, and found to provide potentially useful information about the structure of the interactions of top.Comment: References added and minor discussion improvements; results unchanged; Version to be published in PR