Sol-Gel Derived Ferroelectric Nanoparticles Investigated by Piezoresponse Force Microscopy

Piezoresponse force microscopy (PFM) was used to investigate the ferroelectric properties of sol-gel derived LiNbO$_3$ nanoparticles. To determine the degree of ferroelectricity we took large-area images and performed statistical image-analysis. The ferroelectric behavior of single nanoparticles was verified by poling experiments using the PFM tip. Finally we carried out simultaneous measurements of the in-plane and the out-of-plane piezoresponse of the nanoparticles, followed by measurements of the same area after rotation of the sample by 90$^{\circ}$ and 180$^{\circ}$. Such measurements basically allow to determine the direction of polarization of every single particle

Effects of the R-parity violation in the minimal supersymmetric standard model on dilepton pair production at the CERN LHC

We investigate in detail the effects of the R-parity lepton number violation in the minimal supersymmetric standard model (MSSM) on the parent process $pp \to e^+ e^- + X$ at the CERN Large Hadron Collider (LHC). The numerical comparisons between the contributions of the R-parity violating effects to the parent process via the Drell-Yan subprocess and the gluon-gluon fusion are made. We find that the R-violating effects on $e^+ e^-$ pair production at the LHC could be significant. The results show that the cross section of the $e^+ e^-$ pair productions via gluon-gluon collision at the LHC can be of the order of $10^2$ fb, and this subprocess maybe competitive with the production mechanism via the Drell-Yan subprocess. We give also quantitatively the analysis of the effects from both the mass of sneutrino and coupling strength of the R-parity violating interactions.Comment: 18 pages, 10 figures, accepted by Phys. Rev.

Increased Yield of ttbb at Hadron Colliders in Low-Energy Supersymmetry

Light bottom squarks and gluinos have been invoked to explain the b quark pair production excess at the Tevatron. We investigate the associated production of ttbb at hadron colliders in this scenario, and find that the rates for this process are enhanced over the Standard Model prediction. If light gluinos exist, it may be possible to detect them at the Tevatron, and they could easily be observed at the LHC.Comment: 5p, references added, version accepted to PR

Two Photon Radiation in W and Z Boson Production at the Tevatron Collider

We present a calculation of two photon radiation in W and Z boson production in hadronic collisions, based on the complete matrix elements for the processes q\bar q'\to\ell^\pm\nu\gamma\gamma and q\bar q\to\ell^+\ell^-\gamma\gamma, including finite charged lepton masses. In order to achieve stable numerical results over the full phase space, multiconfiguration Monte Carlo techniques are used to map the peaks in the differential cross section. Numerical results are presented for the Fermilab Tevatron.Comment: Revtex, 28 pages, 3 figure

Prospects for Searching for Excited Leptons during RunII of the Fermilab Tevatron

This letter presents a study of prospects of searching for excited leptons during RunII of the Fermilab Tevatron. We concentrate on single and pair production of excited electrons in the photonic decay channel in one CDF/DO detector equivalent for 2 fb^{-1}. By the end of RunIIa, the limits should be easily extended beyond those set by LEP and HERA for excited leptons with mass above about 190 GeV.Comment: 4 pages, 8 figure

Proton stopping in C+C, d+C, C+Ta and d+Ta collisions at 4.2A GeV/c

The shape of proton rapidity distributions is analysed in terms of their Gaussian components, and the average rapidity loss is determined in order to estimate the amount of stopping in C+C, d+C, C+Ta and d+Ta collisions at 4.2A GeV/c. Three Gaussians correspond to the nuclear transparency and describe well all peripheral and also C+C central collisions. Two-component shape is obtained in case of d+C and C+Ta central collisions. Finally one Gaussian, found in d+Ta central collisions, corresponds to the full stopping. The calculated values of the average rapidity loss support the qualitative relationship between the number of Gaussian components and the corresponding stopping power. It is also observed, in central collisions, that the average rapidity loss increases with the ratio of the number of target and the number of projectile participants.Comment: 9 pages REVTeX, 1 PS figure replaced, to be published in Phys.Rev.

Evaluation of bistable systems versus matched filters in detecting bipolar pulse signals

This paper presents a thorough evaluation of a bistable system versus a matched filter in detecting bipolar pulse signals. The detectability of the bistable system can be optimized by adding noise, i.e. the stochastic resonance (SR) phenomenon. This SR effect is also demonstrated by approximate statistical detection theory of the bistable system and corresponding numerical simulations. Furthermore, the performance comparison results between the bistable system and the matched filter show that (a) the bistable system is more robust than the matched filter in detecting signals with disturbed pulse rates, and (b) the bistable system approaches the performance of the matched filter in detecting unknown arrival times of received signals, with an especially better computational efficiency. These significant results verify the potential applicability of the bistable system in signal detection field.Comment: 15 pages, 9 figures, MikTex v2.

Storage capacity of a constructive learning algorithm

Upper and lower bounds for the typical storage capacity of a constructive algorithm, the Tilinglike Learning Algorithm for the Parity Machine [M. Biehl and M. Opper, Phys. Rev. A {\bf 44} 6888 (1991)], are determined in the asymptotic limit of large training set sizes. The properties of a perceptron with threshold, learning a training set of patterns having a biased distribution of targets, needed as an intermediate step in the capacity calculation, are determined analytically. The lower bound for the capacity, determined with a cavity method, is proportional to the number of hidden units. The upper bound, obtained with the hypothesis of replica symmetry, is close to the one predicted by Mitchinson and Durbin [Biol. Cyber. {\bf 60} 345 (1989)].Comment: 13 pages, 1 figur

Can MSSM with light sbottom and light gluino survive Z-peak constraints ?

In the framework of minimal supersymmetric model we examine the Z-peak constraints on the scenario of one light sbottom (2--5.5 GeV) and light gluino (12--16 GeV), which has been successfully used to explain the excess of bottom quark production in hadron collision. Such a scenario is found to be severely constrained by LEP Z-peak observables, especially by R_b, due to the large effect of gluino-sbottom loops. To account for the R_b data in this scenario, the other mass eigenstate of sbottom, i.e., the heavier one, must be lighter than 125 (195) GeV at 2-sigma (3-sigma) level, which should have been produced in association with the lighter one at LEP II and will probobaly be within the reach of Tevatron Run 2.Comment: discussion on SUSY-EW effects added, to appear in PR

Searching for prompt signatures of nearby core-collapse supernovae by a joint analysis of neutrino and gravitational-wave data

We discuss the science motivations and prospects for a joint analysis of gravitational-wave (GW) and low-energy neutrino data to search for prompt signals from nearby supernovae (SNe). Both gravitational-wave and low-energy neutrinos are expected to be produced in the innermost region of a core-collapse supernova, and a search for coincident signals would probe the processes which power a supernova explosion. It is estimated that the current generation of neutrino and gravitational-wave detectors would be sensitive to Galactic core-collapse supernovae, and would also be able to detect electromagnetically dark SNe. A joint GW-neutrino search would enable improvements to searches by way of lower detection thresholds, larger distance range, better live-time coverage by a network of GW and neutrino detectors, and increased significance of candidate detections. A close collaboration between the GW and neutrino communities for such a search will thus go far toward realizing a much sought-after astrophysics goal of detecting the next nearby supernova.Comment: 10 pages, 3 figures. To appear in Class. Quantum Gra