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## Magneto-transport characteristics of a 2D electron system driven to negative magneto-conductivity by microwave photoexcitation

Mani, R. G.; Kriisa, A.
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Negative diagonal magneto-conductivity/resistivity is a spectacular- and thought provoking-property of driven, far-from-equilibrium, low dimensional electronic systems. The physical response of this exotic electronic state is not yet fully understood since it is rarely encountered in experiment. The microwave-radiation-induced zero-resistance state in the high mobility GaAs/AlGaAs 2D electron system is believed to be an example where negative magneto-conductivity/resistivity is responsible for the observed phenomena. Here, we examine the magneto-transport characteristics of this negative conductivity/resistivity state in the microwave photo-excited two-dimensional electron system (2DES) through a numerical solution of the associated boundary value problem. The results suggest, surprisingly, that a bare negative diagonal conductivity/resistivity state in the 2DES under photo-excitation should yield a positive diagonal resistance, with a concomitant sign reversal in the Hall voltage.

## Restaurant Marquees: A Help or Hindrance'?

Dienhart, John R.; Lefever, Michael M.
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Português
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The marquee is one of the most common and cost-effective forms of advertising, but it can be a restaurant's worst enemy. Here are some surprising facts about its use and misuse.

## Charged Higgs Boson Effects in the Production and Decay of a Heavy Majorana Neutrino at the LHC

Bar-Shalom, Shaouly; Eilam, Gad; Han, Tao; Soni, Amarjit
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We consider a new interaction between a heavy Majorana neutrino (N) and a charged Higgs boson (H+) and show that it can have drastic implications on lepton number violating (LNV) signal of same-sign dileptons at the LHC. The LNV signal of heavy Majorana neutrinos previously considered at the LHC, pp -> l+ N -> l+ l+ W-, may be overwhelmed by pp -> l+ N -> l+ l+ H-. With the subsequent decays H- -> b t(bar) or H- -> W- H^0, the heavy Majorana neutrino production leads to the spectacular events of l+ l+ b b(bar) + 2 jets. We also explore the case m_N < m_{H+}, where the decay H+ -> l+ N can become the dominant N-production mechanism at the LHC. In particular, we show that the process g b -> t H- followed by t -> b W+ and H- -> l- N -> l- l- W+ could lead to another type of spectacular events of l- l- b + 4 jets.; Comment: revtex4, 16 pages, 2 figures

## Waiting for Clear Signals of New Physics in B and K Decays

Buras, Andrzej J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We classify the extensions of the Standard Model (SM) according to the structure of local operators in the weak effective Hamiltonian and the presence or absence of new flavour and CP-violating interactions beyond those represented by the CKM matrix. In particular we review characteristic properties of models with minimal flavour violation (MFV), models with significant contributions from Higgs penguins and models with enhanced Z^0 penguins carrying a large new CP-violating phase. Within the latter models, the anomalous behaviour of certain B\to\pi K observables implies large departures from the SM predictions for rare and CP-violating K and B decays. Most spectacular is the enhancement of Br(K_L->pi^0 nu nubar) by one order of magnitude and a strong violation of the MFV relation (\sin2\beta)_{\pi\nu\bar\nu}=(\sin2\beta)_{\psi K_S}. On the other hand our prediction for (\sin2\beta)_{\phi K_S}\approx 0.9 differs from the Belle result by the sign but is consistent with the BaBar value. We give a personal shopping list for the coming years.; Comment: Main latex-file, 4 figures, 22 pages

## Frozen light in periodic metamaterials

Figotin, A.; Vitebskiy, I.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Wave propagation in spatially periodic media, such as photonic crystals, can be qualitatively different from any uniform substance. The differences are particularly pronounced when the electromagnetic wavelength is comparable to the primitive translation of the periodic structure. In such a case, the periodic medium cannot be assigned any meaningful refractive index. Still, such features as negative refraction and/or opposite phase and group velocities for certain directions of light propagation can be found in almost any photonic crystal. The only reservation is that unlike hypothetical uniform left-handed media, photonic crystals are essentially anisotropic at frequency range of interest. Consider now a plane wave incident on a semi-infinite photonic crystal. One can assume, for instance, that in the case of positive refraction, the normal components of the group and the phase velocities of the transmitted Bloch wave have the same sign, while in the case of negative refraction, those components have opposite signs. What happens if the normal component of the transmitted wave group velocity vanishes? Let us call it a "zero-refraction" case. At first sight, zero normal component of the transmitted wave group velocity implies total reflection of the incident wave. But we demonstrate that total reflection is not the only possibility. Instead...

## Gravitational Shock Waves and Their Scattering in Brane-Induced Gravity

Kaloper, Nemanja
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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In this paper, following hep-th/0501028, we present a detailed derivation and discussion of the exact gravitational field solutions for a relativistic particle localized on a tensional brane in brane-induced gravity. Our derivation yields the metrics for both the normal branch and the self-inflating branch DGP braneworlds. They generalize the 4D gravitational shock waves in de Sitter space, and so we compare them to the corresponding 4D General Relativity solution and to the case when gravity resides only in the 5D bulk, and there are no brane-localized graviton kinetic terms. We write down the solutions in terms of two-variable hypergeometric functions and find that at short distances the shock wave profiles look exactly the same as in 4D Minkowski space, thus recovering the limit one expects if gravity is to be mediated by a metastable, but long-lived, bulk resonance. The corrections far from the source differ from the long distance corrections in 4D de Sitter space, coming in with odd powers of the distance. We discuss in detail the limiting case on the self-inflating branch when gravity is modified exactly at de Sitter radius, and energy can be lost into the bulk by resonance-like processes. Finally, we consider Planckian scattering on the brane...

## Three-body Supersymmetric Top Decays

Belyaev, Alexander; Ellis, John; Lola, Smaragda
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We discuss three-body supersymmetric top decays, in schemes both with and without R-parity conservation, assuming that sfermion masses are larger than m_t. We find that MSSM top decays into chargino/neutralino pairs have a strong kinematic suppression in the region of the supersymmetric parameter space consistent with the LEP limits, with a decay width =< 10^{-5} GeV. MSSM top decays into neutralino pairs have less kinematical suppression, but require a flavour-changing vertex, and are likely to have a smaller rate. On the other hand, R-violating decays to single charginos, neutralinos and conventional fermions can be larger for values of the R-violating couplings still permitted by other upper limits. The cascade decays of the charginos and neutralinos may lead to spectacular signals with explicit lepton-number violation, such as like-sign lepton events.; Comment: CERN-TH/2000-60, 13 pages, LaTex, 10 figures

## Boosting Searches for Natural SUSY with RPV via Gluino Cascades

Han, Zhenyu; Katz, Andrey; Son, Minho; Tweedie, Brock
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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In the presence of even minuscule baryonic R-parity violation, the stop can be the lightest superpartner and evade LHC searches because it decays into two jets. In order to cover this interesting possibility, we here consider new searches for RPV stops produced in gluino cascades. While typical searches for gluinos decaying to stops rely on same-sign dileptons, the RPV cascades usually have fewer hard leptons, less excess missing energy, and more jets than R-parity conserving cascades. If the gluino is a Dirac fermion, same-sign dilepton signals are also often highly depleted. We therefore explore search strategies that use single-lepton channels, and combat backgrounds using HT, jet counting, and more detailed multijet kinematics or jet substructure. We demonstrate that the stop mass peaks can be fully reconstructed over a broad range of spectra, even given the very high jet multiplicities. This would not only serve as a "double-discovery" opportunity, but would also be a spectacular confirmation that the elusive top-partner has been hiding in multijets.; Comment: 26 pages, 6 figures. V2: Constraints from Atlas search for b's are considered and discussed in detail in newly added subsection II E. Other parts of the paper and the conclusions are intact

## Our Milky Way as a Pure-Disk Galaxy -- A Challenge for Galaxy Formation

Shen, Juntai; Rich, R. Michael; Kormendy, John; Howard, Christian D.; De Propris, Roberto; Kunder, Andrea
Tipo: Artigo de Revista Científica
Português
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Bulges are commonly believed to form in the dynamical violence of galaxy collisions and mergers. Here we model the stellar kinematics of the Bulge Radial Velocity Assay (BRAVA), and find no sign that the Milky Way contains a classical bulge formed by scrambling pre-existing disks of stars in major mergers. Rather, the bulge appears to be a bar, seen somewhat end-on, as hinted from its asymmetric boxy shape. We construct a simple but realistic N-body model of the Galaxy that self-consistently develops a bar. The bar immediately buckles and thickens in the vertical direction. As seen from the Sun, the result resembles the boxy bulge of our Galaxy. The model fits the BRAVA stellar kinematic data covering the whole bulge strikingly well with no need for a merger-made classical bulge. The bar in our best fit model has a half-length of ~ 4kpc and extends 20 degrees from the Sun-Galactic Center line. We use the new kinematic constraints to show that any classical bulge contribution cannot be larger than ~ 8% of the disk mass. Thus the Galactic bulge is a part of the disk and not a separate component made in a prior merger. Giant, pure-disk galaxies like our own present a major challenge to the standard picture in which galaxy formation is dominated by hierarchical clustering and galaxy mergers.; Comment: 5 pages; emulateapj format; minor changes to match the ApJL accepted version. A quicktime movie is available to illustrate the spectacular bending instability that gives rise to the boxy pseudobulge: http://www.as.utexas.edu/~shen/movies/2view_bending_inertialframe.mov

## Tracing the merger history of MACS clusters using the GMRT

Paul, S.; Datta, A.; Intema, H. T.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Galaxy-cluster merger shocks efficiently accelerate the ambient electrons through diffusive shock acceleration and amplify magnetic field by compressing the Inter Cluster Medium. As a result, such objects produce a significant amount of synchrotron radio emission. Radio halo and Mpc scale peripheral radio relics thus help us to trace back the cluster formation history. To study the dynamical state of the galaxy clusters and their relation to the merging scenario, as a pilot project, we thus observed four suitable candidates from the MACS (Massive Cluster Survey) cluster sample. Observations were carried out simultaneously at 610 and 235 MHz with the GMRT. We observed a rare phenomena in the cluster MACSJ0014.3-3022, which hosts both a peripheral spectacular radio relic and an unusually flat spectrum central giant radio halo of more than 1.5 Mpc dimension. We also report that another cluster MACSJ0152.5-2852 is possibly showing the sign of one of the earliest and young merging system where, we saw a faint 0.5 Mpc radio relic at the cluster periphery.; Comment: 4 pages, 2 figures, to appear in the proceedings of "The Metrewavelength Sky" conference, held at NCRA-TIFR in Pune, India, from December 9-13, 2013

## Same-sign single dilepton productions at the LHC

Chen, Chian-Shu; Geng, Chao-Qiang; Zhuridov, Dmitry V.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We examine the same-sign single dilepton productions of $\ell_i^{\pm}\ell_j^{\pm} (\ell_{i,j}=e,\mu)$ in high-energy proton-proton collisions at the Large Hadron Collider (LHC) in models with doubly charged Higgs scalars as well as heavy Majorana neutrinos. We demonstrate that these spectacular productions can be detected at the LHC for a class model in which the doubly charged Higgs scalars couple only to the right-handed charged leptons. The ranges of the possible doubly charged Higgs masses and mixings to observe the processes at the LHC are discussed.; Comment: 10 pages, 5 figures

## Optical Outburst of the Gamma-Ray Blazar S4 0954+658 in March-April 2011

Larionov, V. M.; Jorstad, S. G.; Marscher, A. P.; Morozova, D. A.; Troitsky, I. S.; Blinov, D. A.; Kopatskaya, E. N.; Larionova, E. G.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We present optical photopolarimetric observations of the BL Lac object S4 0954+658 obtained with the 70-cm telescope in Crimea, 40-cm telescope in St.Petersburg, and 1.8-m Perkins telescope at Lowell Observatory (Flagstaff, Az). After a faint state with a brightness level R ~17.6 mag registered in the first half of January 2011, the optical brightness of the source started to rise and reached ~14.8 mag during the middle of March, showing flare-like behavior. The most spectacular case of intranight variability was observed during the night of 2011 March 9, when the blazar brightened by ~0.7 mag within ~7 hours. During the rise of the flux the position angle of optical polarization rotated smoothly over more than 200 degrees. S4 0954+658 is a gamma-ray blazar with gamma-ray flux of (5{\pm}3)x10^{-10} phot/cm^2/s according to the Fermi 11-month Catalog Extragalactic Sources. Our analysis of contemporaneous Fermi LAT data does not show any sign of increased gamma-ray activity above the detection threshold except for an elevated flux on 2011 March 5, JD2455626, coincident with the local optical maximum.; Comment: 2011 Fermi Symposium proceedings - eConf C110509

## Neutralino dark matter confronted by the LHC constraints on Electroweak SUSY signals

Choudhury, Arghya; Datta, Amitava
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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The supersymmetric particles (sparticles) belonging exclusively to the electroweak sector of the minimal supersymmetric standard model (MSSM) may hold the key to the observed dark matter relic density in the universe even if all strongly interacting sparticles are very heavy. The importance of the light EW sparticles in DM physics and in producing spectacular collider signals is emphasized. It is shown that even the preliminary data on the direct searches of these sparticles at the LHC, significantly constrain the parameter space of the MSSM compatible with the observed relic density and provide useful hints about the future search prospects. If in addition to the electroweak sparticles the gluinos are also within the reach of the LHC experiments, then the gluino mass limits in the light slepton scenario obtained via the canonical jets + $\met$ channel may be relaxed by as much as 25 $%$ compared to the existing limits. But the corresponding same sign dilepton (SSD) + jets + $\met$ signal will yield enhanced limits competitive with the strongest limits currently available. This is illustrated with the help of benchmark scenarios at the generator level using PYTHIA. If the gluinos are just beyond the current reach of the LHC, then the generic n-lepton + m-jets + missing energy signal may discriminate between different DM producing mechanisms by comparing the signals corresponding to different values of n. This is illustrated by simulating the signals for n = 0 and n = 2 (the SSD signal).; Comment: 37 pages...

## New Signals for Gluinos and Squarks of Supergravity at the Tevatron Collider

Baer, H.; Kao, C.; Tata, X.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Within the supergravity framework, sleptons are expected to be considerably lighter than squarks if gluinos and squarks are approximately degenerate. This can lead to a significant enhancement in leptonic branching ratio for neutralinos, and sometimes, charginos. Using ISAJET 7.0/ISASUSY 1.0, we evaluate the multilepton signals from cascade decays of gluinos and squarks produced at the Fermilab Tevatron $p\bar p$ collider assuming squark and slepton masses are related as in supergravity models. We find observable cross sections for spectacular event topologies: $m$-lepton + $n$-jet + $\eslt$ events ($m \leq 4$, $n \geq 2$) and same-sign dilepton + $\eslt$ events and show that the SM backgrounds to the isolated trilepton, four lepton and same-sign dilepton signals are very small. These signals can extend the mass reach of the Tevatron experiments to $m_{\tg}\sim 300$~GeV if $m_{\tg}\sim m_{\tq}$ and ${\cal O}(1000)$ pb$^{-1}$ of data are collected.; Comment: 14 pages plus 2 figures available upon request (revtex file), FSU-HEP-930527

## Transport and magnetic properties of GdBaCo_{2}O_{5+x} single crystals: A cobalt oxide with square-lattice CoO_2 planes over a wide range of electron and hole doping

Taskin, A. A.; Lavrov, A. N.; Ando, Yoichi
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Single crystals of the layered perovskite GdBaCo_{2}O_{5+x} (GBCO) have been grown by the floating-zone method, and their transport, magnetic, and structural properties have been studied in detail over a wide range of oxygen contents. The obtained data are used to establish a rich phase diagram centered at the "parent'' compound GdBaCo_{2}O_{5.5} -- an insulator with Co ions in the 3+ state. An attractive feature of GBCO is that it allows a precise and continuous doping of CoO_{2} planes with either electrons or holes, spanning a wide range from the charge-ordered insulator at 50% electron doping (x=0) to the undoped band insulator (x=0.5), and further towards the heavily hole-doped metallic state. This continuous doping is clearly manifested in the behavior of thermoelectric power which exhibits a spectacular divergence with approaching x=0.5, where it reaches large absolute values and abruptly changes its sign. At low temperatures, the homogeneous distribution of doped carriers in GBCO becomes unstable, and both the magnetic and transport properties point to an intriguing nanoscopic phase separation. We also find that throughout the composition range the magnetic behavior in GBCO is governed by a delicate balance between ferromagnetic (FM) and antiferromagnetic (AF) interactions...

## Magneto-transport characteristics of a 2D electron system driven to negative magneto-conductivity by microwave photoexcitation

Mani, R. G.; Kriisa, A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
17.016934%
Negative diagonal magneto-conductivity/resistivity is a spectacular- and thought provoking- property of driven, far-from-equilibrium, low dimensional electronic systems. The physical response of this exotic electronic state is not yet fully understood since it is rarely encountered in experiment. The microwave-radiation-induced zero-resistance state in the high mobility GaAs/AlGaAs 2D electron system is believed to be an example where negative magneto-conductivity/resistivity is responsible for the observed phenomena. Here, we examine the magneto-transport characteristics of this negative conductivity/resistivity state in the microwave photo-excited two-dimensional electron system (2DES) through a numerical solution of the associated boundary value problem. The results suggest, surprisingly, that a bare negative diagonal conductivity/resistivity state in the 2DES under photo-excitation should yield a positive diagonal resistance with a concomitant sign reversal in the Hall voltage.; Comment: 5 color figures

## Tau Signals of R-parity breaking at LEP 200

Godbole, Rohini M.; Roy, Probir; Tata, Xerxes
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The detectability at LEP 200 of explicit $R$-parity breaking by tau-number $(L_\tau)$ violating operators is considered. The assumption of $L_\tau$-violation is motivated by the relative lack of constraints on such couplings but similar considerations apply to explicit $L_e$- or $L_\mu$-violation. The $LSP$, now unstable, and not necessarily neutral, decays via $L_\tau$-violating modes. Only signals from the production and decays of $LSP$ pairs are considered, thereby avoiding any dependence on the sparticle mass spectrum. Rather spectacular signals are predicted: spherical events with $m$ leptons (usually containing at least one $\tau$) and $n$ jets $(m,n \leq 4)$, the most characteristic of which are like-sign $\tau\tau$ events. These signals are enumerated for each $LSP$ candidate and quantitative estimates are provided for the favoured case when the $LSP$ is a neutralino. Other new physics signals, which can mimic these signatures, are also briefly discussed.; Comment: 27 pages in PHYZZX, six figures (not included, available on request). TIFR/TH/92-29,UH-511-751-92,CERN-TH.6613/92

## Seesaw at LHC through Left - Right Symmetry

Senjanovic, Goran
Tipo: Artigo de Revista Científica
Português
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I argue that LHC may shed light on the nature of neutrino mass through the probe of the seesaw mechanism. The smoking gun signature is lepton number violation through the production of same sign lepton pairs, a collider analogy of the neutrinoless double beta decay. I discuss this in the context of L-R symmetric theories, which led originally to neutrino mass and the seesaw mechanism. A W_R gauge boson with a mass in a few TeV region could easily dominate neutrinoless double beta decay, and its discovery at LHC would have spectacular signatures of parity restoration and lepton number violation. Moreover, LHC can measure the masses of the right-handed neutrinos and the right-handed leptonic mixing matrix, which could in turn be used to predict the rates for neutrinoless double decay and lepton flavor violating violating processes. The LR scale at the LHC energies offers great hope of observing these low energy processes in the present and upcoming experiments.; Comment: 14 pages. Based on the plenary talk at the Conference in Honour of Murray Gell-Mann's 80th Birthday, NTU, Singapore, February 2010. Added discussion on mirror fermions, additional references. The version to appear in the International Journal of Modern Physics A

## Brane-Induced Gravity's Shocks

Kaloper, Nemanja
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
17.016934%
We construct exact gravitational field solutions for a relativistic particle localized on a tensional brane in brane-induced gravity. They are a generalization of gravitational shock waves in 4D de Sitter space. We provide the metrics for both the normal branch and the self-inflating branch DGP braneworlds, and compare them to the 4D Einstein gravity solution and to the case when gravity resides only in the 5D bulk, without any brane-localized curvature terms. At short distances the wave profile looks the same as in four dimensions. The corrections appear only far from the source, where they differ from the long distance corrections in 4D de Sitter space. We also discover a new non-perturbative channel for energy emission into the bulk from the self-inflating branch, when gravity is modified at the de Sitter radius.; Comment: 4 pages, revtex4; v4: a sign error corrected; the correction tantamount to swapping normal and self-inflating branch solutions; the only significant change is that the spectacular new instability is on the self-inflating branch in the limit of vanishing brane tension; more details available in hep-th/0502035

Alsalti, Wesam