5,914 research outputs found

    Static Analysis of Parity Games: Alternating Reachability Under Parity

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    It is well understood that solving parity games is equivalent, up to polynomial time, to model checking of the modal mu-calculus. It is a long-standing open problem whether solving parity games (or model checking modal mu-calculus formulas) can be done in polynomial time. A recent approach to studying this problem has been the design of partial solvers, algorithms that run in polynomial time and that may only solve parts of a parity game. Although it was shown that such partial solvers can completely solve many practical benchmarks, the design of such partial solvers was somewhat ad hoc, limiting a deeper understanding of the potential of that approach. We here mean to provide such robust foundations for deeper analysis through a new form of game, alternating reachability under parity. We prove the determinacy of these games and use this determinacy to define, for each player, a monotone fixed point over an ordered domain of height linear in the size of the parity game such that all nodes in its greatest fixed point are won by said player in the parity game. We show, through theoretical and experimental work, that such greatest fixed points and their computation leads to partial solvers that run in polynomial time. These partial solvers are based on established principles of static analysis and are more effective than partial solvers studied in extant work

    Analyzing the Fierz Rearrangement Freedom for Local Chiral Two-Nucleon Potentials

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    Chiral effective field theory is a framework to derive systematic nuclear interactions. It is based on the symmetries of quantum chromodynamics and includes long-range pion physics explicitly, while shorter-range physics is expanded in a general operator basis. The number of low-energy couplings at a particular order in the expansion can be reduced by exploiting the fact that nucleons are fermions and therefore obey the Pauli exclusion principle. The antisymmetry permits the selection of a subset of the allowed contact operators at a given order. When local regulators are used for these short-range interactions, however, this "Fierz rearrangement freedom" is violated. In this paper, we investigate the impact of this violation at leading order (LO) in the chiral expansion. We construct LO and next-to-leading order (NLO) potentials for all possible LO-operator pairs and study their reproduction of phase shifts, the 4{}^4He ground-state energy, and the neutron-matter energy at different densities. We demonstrate that the Fierz rearrangement freedom is partially restored at NLO where subleading contact interactions enter. We also discuss implications for local chiral three-nucleon interactions.Comment: 11 pages, 5 figure

    The Fast Wandering of Slow Birds

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    I study a single "slow" bird moving with a flock of birds of a different, and faster (or slower) species. I find that every "species" of flocker has a characteristic speed γv0\gamma\ne v_0, where v0v_0 is the mean speed of the flock, such that, if the speed vsv_s of the "slow" bird equals γ\gamma, it will randomly wander transverse to the mean direction of flock motion far faster than the other birds will: its mean-squared transverse displacement will grow in d=2d=2 with time tt like t5/3t^{5/3}, in contrast to t4/3t^{4/3} for the other birds. In d=3d=3, the slow bird's mean squared transverse displacement grows like t5/4t^{5/4}, in contrast to tt for the other birds. If vsγv_s\neq \gamma, the mean-squared displacement of the "slow" bird crosses over from t5/2t^{5/2} to t4/3t^{4/3} scaling in d=2d=2, and from t5/4t^{5/4} to tt scaling in d=3d=3, at a time tct_c that scales according to tcvsγ2t_c \propto|v_s-\gamma|^{-2}.Comment: 10 pages; 5 pages of which did not appear in earlier versions, but were added in response to referee's suggestion

    Searching for t-bar t Resonances at the Large Hadron Collider

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    Many new physics models predict resonances with masses in the TeV range which decay into a pair of top quarks. With its large cross section, t-bar t production at the Large Hadron Collider (LHC) offers an excellent opportunity to search for such particles. We present a detailed study of the discovery potential of the CERN Large Hadron Collider for Kaluza-Klein (KK) excitations of the gluon in bulk Randall-Sundrum (RS) models in the t-bar t -> ell^+/- nu b-bar bq-bar q' (ell=e, mu) final state. We utilize final states with one or two tagged b-quarks, and two, three or four jets (including b-jets). Our calculations take into account the finite resolution of detectors, the energy loss due to b-quark decays, the expected reduced b-tagging efficiency at large t-bar t invariant masses, and include the background originating from Wb-bar b+jets, (Wb+W-bar b)+jets, W+jets, and single top + jets production. We derive semi-realistic 5 sigma discovery limits for nine different KK gluon scenarios, and compare them with those for KK gravitons, and a Z_H boson in the Littlest Higgs model. We also analyze the capabilities of the LHC experiments to differentiate between individual KK gluon models and measure the couplings of KK gluons to quarks. We find that, for the parameters and models chosen, KK gluons with masses up to about 4 TeV can be discovered at the LHC. The ability of the LHC to discriminate between different bulk RS models, and to measure the couplings of the KK gluons is found to be highly model dependent.Comment: revtex3, 27 pages, 5 tables, 6 figure

    Relationships of surface air temperature anomalies over Europe to persistence of atmospheric circulation patterns conducive to heat waves

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    Heat waves are among natural hazards with the most severe consequences for human society, including pronounced mortality impacts in mid-latitudes. Recent studies have hypothesized that the enhanced persistence of atmospheric circulation may affect surface climatic extremes, mainly the frequency and severity of heat waves. In this paper we examine relationships between the persistence of the Hess-Brezowsky circulation types conducive to summer heat waves and air temperature anomalies at stations over most of the European continent. We also evaluate differences between temperature anomalies during late and early stages of warm circulation types in all seasons. Results show that more persistent circulation patterns tend to enhance the severity of heat waves and support more pronounced temperature anomalies. Recent sharply rising trends in positive temperature extremes over Europe may be related to the greater persistence of the circulation types, and if similar changes towards enhanced persistence affect other mid-latitudinal regions, analogous consequences and implications for temperature extremes may be expected

    Jet shapes in ep collisions at HERA

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    New measurements of the jet shape in ep collisions at HERA using the k_T-cluster jet algorithm are presented.Comment: 7 pages, 3 figures; plenary talk given at the 3rd UK Phenomenology Workshop on HERA Physics, Durham, UK, September 199

    Warped Gravitons at the LHC and Beyond

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    We study the production and decay of Kaluza-Klein (KK) gravitons at the Large Hadron Collider (LHC), in the framework of a warped extra dimension in which the Standard Model (SM) fields propagate. Such a scenario can provide solutions to both the Planck-weak hierarchy problem and the flavor puzzle of the SM. In this scenario, the production via qqˉq \bar{q} annihilation and decays to the conventional photon and lepton channels are highly suppressed. However, we show that graviton production via gluon fusion followed by decay to longitudinal Z/WZ/W can be significant; vector boson fusion is found to be a sub-dominant production mode. In particular, the ``golden'' ZZZZ decay mode offers a distinctive 4-lepton signal that could lead to the observation at the LHC with 300 fb1^{-1} (SLHC with 3 ab1^{-1}) of a KK graviton with a mass up to 2\sim 2 (3\sim 3) TeV for the ratio of the AdS5_5 curvature to the Planck scale modestly above unity. We argue that (contrary to the lore) such a size of the curvature scale can still be within the regime of validity of the framework. Upgrades beyond the SLHC luminosity are required to discover gravitons heavier than 4\sim 4 TeV, as favored by the electroweak and flavor precision tests in the simplest such models.Comment: 9 pages, 5 figures. Minor modifications, reference adde

    Factorization for generic jet production

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    Factorization is the central ingredient in any theoretical prediction for collider experiments. We introduce a factorization formalism that can be applied to any desired observable, like event shapes or jet observables, for any number of jets and a wide range of jet algorithms in leptonic or hadronic collisions. This is achieved by using soft-collinear effective theory to prove the formal factorization of a generic fully-differential cross section in terms of a hard coefficient, and generic jet and soft functions. In this formalism, whether a given observable factorizes in the usual sense, depends on whether it is inclusive enough, so the jet functions can be calculated perturbatively. The factorization formula for any such observable immediately follows from our general result, including the precise definition of the jet and soft functions appropriate for the observable in question. As examples of our formalism, we work out several results in two-jet production for both e+e- and pp collisions. For the latter, we also comment on how our formalism allows one to treat underlying events and beam remnants.Comment: 33 pages, v2: minor typos corrected, journal versio

    Engineering evaluations and studies. Report for Ku-band studies, exhibit A

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    System performance aspects of the Ku band radar communication hardware and investigations into the Ku band/payload interfaces are discussed. The communications track problem caused by the excessive signal dynamic range at the servo input was investigated. The management/handover logic is discussed and a simplified description of the transmitter enable logic function is presented. Output noise produced by a voltage-controlled oscillator chip used in the SPA return-link channel 3 mid-bit detector is discussed. The deployed assembly (DA) and EA-2 critical design review data are evaluated. Cross coupling effects on antenna servo stability were examined. A series of meetings on the acceptance test specification for the deployed assembly is summarized

    A Reanalysis of the Hydrodynamic Theory of Fluid, Polar-Ordered Flocks

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    I reanalyze the hydrodynamic theory of fluid, polar ordered flocks. I find new linear terms in the hydrodynamic equations which slightly modify the anisotropy, but not the scaling, of the damping of sound modes. I also find that the nonlinearities allowed {\it in equilibrium} do not stabilize long ranged order in spatial dimensions d=2d=2; in accord with the Mermin-Wagner theorem. Nonequilibrium nonlinearities {\it do} stabilize long ranged order in d=2d=2, as argued by earlier work. Some of these were missed by earlier work; it is unclear whether or not they change the scaling exponents in d=2d=2.Comment: 6 pages, no figures. arXiv admin note: text overlap with arXiv:0909.195
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