1,610 research outputs found

    Black hole binaries in cubic Horndeski theories

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    We study black hole binary mergers in certain cubic Horndeski theories of gravity, treating them fully nonlinearly. In the regime of validity of effective field theory, the mismatch of the gravitational wave strain between Horndeski and general relativity (coupled to a scalar field) can be as large as 10%-13% in the Advanced LIGO mass range. The initial data and coupling constants are chosen such the theory remains in the weakly coupled regime throughout the evolution. In all cases that we have explored, we observe that the waveform in the Horndeski theory is shifted by an amount much larger than the smallness parameter that controls the initial data. This effect is generic and may be present in other theories of gravity involving higher derivatives

    Stable non-uniform black strings below the critical dimension

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    The higher-dimensional vacuum Einstein equation admits translationally non-uniform black string solutions. It has been argued that infinitesimally non-uniform black strings should be unstable in 13 or fewer dimensions and otherwise stable. We construct numerically non-uniform black string solutions in 11, 12, 13, 14 and 15 dimensions. Their stability is investigated using local Penrose inequalities. Weakly non-uniform solutions behave as expected. However, in 12 and 13 dimensions, strongly non-uniform solutions appear to be stable and can have greater horizon area than a uniform string of the same mass. In 14 and 15 dimensions all non-uniform black strings appear to be stable.Comment: 26 pages, 11 figures. V2: reference added, matches published versio

    Trust and trustworthiness under information asymmetry and ambiguity

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    We introduce uncertainty and ambiguity in the standard investment game. In the uncertainty treatment, investors are informed that the return of the investment is drawn from a publicly known distribution function. In the ambiguity treatment, investors are not informed about the distribution function. We find that both trust and trustworthiness are robust to the introduction of these changes

    Information asymmetry and deception

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    Situations such as an entrepreneur overstating a project’s value, or a superior choosing to under or overstate the gains from a project to a subordinate are common and may result in acts of deception. In this paper we modify the standard investment game in the economics literature to study the nature of deception. In this game a trustor (investor) can send a given amount of money to a trustee (or investee). The amount received is multiplied by a certain amount, k, and the investee then decides on how to divide the total amount received. In our modified game the information on the multiplier, k, is known only to the investee and she can send a nonbinding message to the investor regarding its value. We find that 66% of the investees send false messages with both under and over, statement being observed. Investors are naive and almost half of them believe the message received. We find greater lying when the distribution of the multiplier is unknown by the investors than when they know the distribution. Further, messages make beliefs about the multiplier more pessimistic when the investors know the distribution of the multiplier, while the opposite is true when they do not know the distribution

    Real-Time Dynamics of Plasma Balls from Holography

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    Plasma balls are droplets of deconfined plasma surrounded by a confining vacuum. We present the first holographic simulation of their real-time evolution via the dynamics of localized, finite-energy black holes in the five-dimensional anti–de Sitter (AdS) soliton background. The dual gauge theory is four-dimensional N = 4 super Yang-Mills theory compactified on a circle with supersymmetry-breaking boundary conditions. We consider horizonless initial data sourced by a massless scalar field. Prompt scalar field collapse produces an excited black hole at the bottom of the geometry together with gravitational and scalar radiation. The radiation disperses to infinity in the noncompact directions and corresponds to particle production in the dual gauge theory. The black hole evolves toward the dual of an equilibrium plasma ball on a time scale longer than naively expected. This feature is a direct consequence of confinement and is caused by long-lived, periodic disturbances bouncing between the bottom of the AdS soliton and the AdS boundary

    Nonspherically Symmetric Collapse in Asymptotically AdS Spacetimes

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    We numerically simulate gravitational collapse in asymptotically anti-de Sitter spacetimes away from spherical symmetry. Starting from initial data sourced by a massless real scalar field, we solve the Einstein equations with a negative cosmological constant in five spacetime dimensions and obtain a family of non-spherically symmetric solutions, including those that form two distinct black holes on the axis. We find that these configurations collapse faster than spherically symmetric ones of the same mass and radial compactness. Similarly, they require less mass to collapse within a fixed time

    Absolute magnitudes and kinematics of CP stars from Hipparcos data

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    The position in the HR diagram and the kinematic characteristics of different kinds of CP stars of the upper main sequence are obtained using the LM method (Luri et al., 1996). Most of the CP stars are main sequence stars occupying the whole width of the sequence. From a kinematic point of view, they belong to the young disk population (ages < 1.5 Gyr). It has also been found that, on kinematic grounds, the behaviour of lambda Bootis stars is similar to the one observed for normal stars of the same spectral range. On the other hand, roAp and noAp stars show the same kinematic characteristics. The peculiar velocity distribution function has been decomposed into a sum of three dimensional gaussians and the presence of Pleiades, Sirius and Hyades moving groups has been clearly established. Finally, a small number of CP stars are found to be high-velocity objects.Comment: 8 pages, 1 figure, to appear in: Proc. of the 26th workshop of the European Working Group on CP stars, eds. P. North, A. Schnell and J. Ziznovsky, Contrib. Astr. Obs. Skalnate Pleso Vol. 27, No

    Non-abelian magnetic black strings versus black holes

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    We present d+1d+1-dimensional pure magnetic Yang-Mills (YM) black strings (or 11-branes) induced by the dd-dimensional Einstein-Yang-Mills-Dilaton black holes. Born-Infeld version of the YM field makes our starting point which goes to the standard YM field through a limiting procedure. The lifting from black holes to black strings, (with less number of fields) is by adding an extra, compact coordinate. This amounts to the change of horizon topology from Sd2S^{d-2} to a product structure. Our black string in 55-dimensions is a rather special one, with uniform Hawking temperature and non-asymptotically flat structure. As the YM charge becomes large the string gets thinner to tend into a breaking point and transform into a 44-% dimensional black hole.Comment: 5 pages no figure; Final version to appear in EPJ
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