16,929 research outputs found

    Is the New Resonance Spin 0 or 2? Taking a Step Forward in the Higgs Boson Discovery

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    The observation of a new boson of mass \sim 125\gev at the CERN LHC may finally have revealed the existence of a Higgs boson. Now we have the opportunity to scrutinize its properties, determining its quantum numbers and couplings to the standard model particles, in order to confirm or not its discovery. We show that by the end of the 8 TeV run, combining the entire data sets of ATLAS and CMS, it will be possible to discriminate between the following discovery alternatives: a scalar JP=0+J^P=0^+ or a tensor JP=2+J^P=2^+ particle with minimal couplings to photons, at a 5σ5\sigma statistical confidence level at least, using only diphotons events. Our results are based on the calculation of a center-edge asymmetry measure of the reconstructed {\it sPlot} scattering polar angle of the diphotons. The results based on asymmetries are shown to be rather robust against systematic uncertainties with comparable discrimination power to a log likelihood ratio statistic.Comment: 11 pages, 6 figures, 1 table. References added, minor typos correcte

    Activity Dependent Branching Ratios in Stocks, Solar X-ray Flux, and the Bak-Tang-Wiesenfeld Sandpile Model

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    We define an activity dependent branching ratio that allows comparison of different time series XtX_{t}. The branching ratio bxb_x is defined as bx=E[ξx/x]b_x= E[\xi_x/x]. The random variable ξx\xi_x is the value of the next signal given that the previous one is equal to xx, so ξx={Xt+1Xt=x}\xi_x=\{X_{t+1}|X_t=x\}. If bx>1b_x>1, the process is on average supercritical when the signal is equal to xx, while if bx<1b_x<1, it is subcritical. For stock prices we find bx=1b_x=1 within statistical uncertainty, for all xx, consistent with an ``efficient market hypothesis''. For stock volumes, solar X-ray flux intensities, and the Bak-Tang-Wiesenfeld (BTW) sandpile model, bxb_x is supercritical for small values of activity and subcritical for the largest ones, indicating a tendency to return to a typical value. For stock volumes this tendency has an approximate power law behavior. For solar X-ray flux and the BTW model, there is a broad regime of activity where bx1b_x \simeq 1, which we interpret as an indicator of critical behavior. This is true despite different underlying probability distributions for XtX_t, and for ξx\xi_x. For the BTW model the distribution of ξx\xi_x is Gaussian, for xx sufficiently larger than one, and its variance grows linearly with xx. Hence, the activity in the BTW model obeys a central limit theorem when sampling over past histories. The broad region of activity where bxb_x is close to one disappears once bulk dissipation is introduced in the BTW model -- supporting our hypothesis that it is an indicator of criticality.Comment: 7 pages, 11 figure

    Standard Model Top Quark Asymmetry at the Fermilab Tevatron

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    Top quark pair production at proton-antiproton colliders is known to exhibit a forward-backward asymmetry due to higher-order QCD effects. We explore how this asymmetry might be studied at the Fermilab Tevatron, including how the asymmetry depends on the kinematics of extra hard partons. We consider results for top quark pair events with one and two additional hard jets. We further note that a similar asymmetry, correlated with the presence of jets, arises in specific models for parton showers in Monte Carlo simulations. We conclude that the measurement of this asymmetry at the Tevatron will be challenging, but important both for our understanding of QCD and for our efforts to model it.Comment: 26 p., 10 embedded figs., comment added, version to appear in PR

    Wong-Zakai approximation of solutions to reflecting stochastic differential equations on domains in Euclidean spaces II

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    The strong convergence of Wong-Zakai approximations of the solution to the reflecting stochastic differential equations was studied in [2]. We continue the study and prove the strong convergence under weaker assumptions on the domain.Comment: To appear in "Stochastic Analysis and Applications 2014-In Honour of Terry Lyons", Springer Proceedings in Mathematics and Statistic

    Changes in the diet and body size of a small herbivorous mammal (hispid cotton rat, \u3ci\u3eSigmodon hispidus\u3c/i\u3e) following the late Pleistocene megafauna extinction

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    The catastrophic loss of large-bodied mammals during the terminal Pleistocene likely led to cascading effects within communities. While the extinction of the top consumers probably expanded the resources available to survivors of all body sizes, little work has focused on the responses of the smallest mammals. Here, we use a detailed fossil record from the southwestern United States to examine the response of the hispid cotton rat Sigmodon hispidus to biodiversity loss and climatic change over the late Quaternary. In particular, we focus on changes in diet and body size. We characterize diet through carbon (δ13C) and nitrogen (δ15N) isotope analysis of bone collagen in fossil jaws and body size through measurement of fossil teeth; the abundance of material allows us to examine population level responses at millennial scale for the past 16 ka. Sigmodon was not present at the cave during the full glacial, first appearing at ~16 ka after ice sheets were in retreat. It remained relatively rare until ~12 ka when warming tempera­tures allowed it to expand its species range northward. We find variation in both diet and body size of Sigmodon hispidus over time: the average body size of the population varied by ~20% (90–110 g) and mean δ13C and δ15N values ranged between −13.5 to −16.5‰ and 5.5 to 7.4‰ respectively. A state–space model suggested changes in mass were influenced by diet, maximum temperature and community structure, while the modest changes in diet were most influenced by community structure. Sigmodon maintained a fairly similar dietary niche over time despite contemporaneous changes in climate and herbivore community composition that followed the megafauna extinc­tion. Broadly, our results suggest that small mammals may be as sensitive to shifts in local biotic interactions within their ecosystem as they are to changes in climate and large-scale biodiversity loss

    Raman Response in Doped Antiferromagnets

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    The resonant part of the B1gB_{1g} electronic Raman scattering response is calculated within the tJt-J model on a planar lattice as a function of temperature and hole doping, using a finite-temperature diagonalization method for small systems. Results, directly applicable to experiments on cuprates, reveal on doping a very pronounced increase of the width of the two-magnon Raman peak, accompanied by a decrease of the total intensity. At the same time the peak position does not shift substantially in the underdoped regime.Comment: 11 pages revtex, 3 postscript figures. Minor corrections and changes from previous version, to be published in Phys. Rev.
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