Dark matter as integration constant in Horava-Lifshitz gravity

In the non-relativistic theory of gravitation recently proposed by Horava, the Hamiltonian constraint is not a local equation satisfied at each spatial point but an equation integrated over a whole space. The global Hamiltonian constraint is less restrictive than its local version, and allows a richer set of solutions than in general relativity. We show that a component which behaves like pressureless dust emerges as an "integration constant" of dynamical equations and momentum constraint equations. Consequently, classical solutions to the infrared limit of Horava-Lifshitz gravity can mimic general relativity plus cold dark matter.Comment: 16 pages; (non-)conservation equation for "dark matter" added (v2); note added to comment on some recent preprints (v3); version accepted for publication in PRD (v4

Long Live the Lie Bill!

What successful defamation plaintiffs typically desire and doctrinally deserve is to have their reputations restored. Presently, however, a plaintiff who has established that she was defamed by the defendant is entitled only to an award of damages, which does nothing to restore reputation. This Note proposes that in addition to a damages award, courts-- if they are to take seriously their obligation to compensate the plaintiff-- should order the defendant to retract the defamatory statement. Contrary to the prevailing view, this Note argues that the proposed retraction order does not jeopardize the First Amendment guarantee of free expression

Adiabatic quantum computation and quantum phase transitions

We analyze the ground state entanglement in a quantum adiabatic evolution algorithm designed to solve the NP-complete Exact Cover problem. The entropy of entanglement seems to obey linear and universal scaling at the point where the mass gap becomes small, suggesting that the system passes near a quantum phase transition. Such a large scaling of entanglement suggests that the effective connectivity of the system diverges as the number of qubits goes to infinity and that this algorithm cannot be efficiently simulated by classical means. On the other hand, entanglement in Grover's algorithm is bounded by a constant.Comment: 5 pages, 4 figures, accepted for publication in PR

Bigravity and Lorentz-violating Massive Gravity

Bigravity is a natural arena where a non-linear theory of massive gravity can be formulated. If the interaction between the metrics $f$ and $g$ is non-derivative, spherically symmetric exact solutions can be found. At large distances from the origin, these are generically Lorentz-breaking bi-flat solutions (provided that the corresponding vacuum energies are adjusted appropriately). The spectrum of linearized perturbations around such backgrounds contains a massless as well as a massive graviton, with {\em two} physical polarizations each. There are no propagating vectors or scalars, and the theory is ghost free (as happens with certain massive gravities with explicit breaking of Lorentz invariance). At the linearized level, corrections to GR are proportional to the square of the graviton mass, and so there is no vDVZ discontinuity. Surprisingly, the solution of linear theory for a static spherically symmetric source does {\em not} agree with the linearization of any of the known exact solutions. The latter coincide with the standard Schwarzschild-(A)dS solutions of General Relativity, with no corrections at all. Another interesting class of solutions is obtained where $f$ and $g$ are proportional to each other. The case of bi-de Sitter solutions is analyzed in some detail.Comment: 25 pages. v3 Typos corrected, references added. v4 Introduction extende

Simple proof of equivalence between adiabatic quantum computation and the circuit model

We prove the equivalence between adiabatic quantum computation and quantum computation in the circuit model. An explicit adiabatic computation procedure is given that generates a ground state from which the answer can be extracted. The amount of time needed is evaluated by computing the gap. We show that the procedure is computationally efficient.Comment: 5 pages, 2 figures. v2: improved gap estimates and added some more detail

Spontaneous Lorentz Breaking and Massive Gravity

We study a theory where the presence of an extra spin-two field coupled to gravity gives rise to a phase with spontaneously broken Lorentz symmetry. In this phase gravity is massive, and the Weak Equivalence Principle is respected. The newtonian potentials are in general modified, but we identify an non-perturbative symmetry that protects them. The gravitational waves sector has a rich phenomenology: sources emit a combination of massless and massive gravitons that propagate with distinct velocities and also oscillate. Since their velocities differ from the speed of light, the time of flight difference between gravitons and photons from a common source could be measured.Comment: 4 page

Liderança critica aplicada através da lens latinas: um abordagem alternativo do liderança educacional

The aims and objectives of this research were to investigate and better understand ways in which race and gender play out as differences of significant consequence in applied leadership practice. Utilizing qualitative case study methodology coupled with counter-story, a critical race theory approach, the authors analyze data on two Mexican descent educational leaders in the US: one Latino K-6 principal and one Chicana university Dean. Findings indicate evidence supporting positive identity leadership traits as practiced through raced and gender lenses, resulting in effective socially just and equitable leadership outcomes for the participants in the study. These findings are new and particularly relevant as demographic shifts in the US and the world include high numbers of Latino/a and Mexican descent individuals. The strategies employed by participants suggest subaltern ways of educational leadership not previously considered in research and literature. The authors discuss evidence of characteristics supporting applied critical leadership (ACL), an emerging leadership theory, in the leadership practices of the participants. Finally, mainstream implications and guidelines are provided for application in multiple educational leadership contextsEl propósito y objetivos de esta investigación fueron investigar y comprender mejor las formas en las que la raza y el género generan importantes consecuencias en la práctica del liderazgo aplicado. Se realiza un estudio de caso cualitativo con contra-historia con un enfoque teórico-crítico sobre raza,. Los autores analizan datos sobre dos líderes educativos de ascendencia mexicana en los EE.UU.: uno director de una escuela K-6 latina y el otro, director de una universidad chicana. Los hallazgos evidencian rasgos de identidad positiva de los líderes que permite la puesta en práctica de un liderazgo equitativo y socialmente justo entre los participantes del estudio. Estos hallazgos son novedosos y especialmente relevantes en EEUU y en el resto de países donde viven un alto número de descendientes de latinos y mexicanos. Las estrategias empleadas por los participantes sugieren alternar formas de liderazgo no consideradas ni en la investigación ni en la literatura. Los autores discuten las evidencias encontradas que definen la teoría emergente del liderazgo crítico aplicado (ACL). Por último, se aportan directrices para su aplicación en diferentes contextosA finalidade e objetivos desta pesquisa foram investigar e entender melhor as maneiras em que raça e gênero têm implicações importantes para a prática da liderança aplicada. Foi feito um estudo de caso qualitativo com contra-história é com uma abordagem teórica e crítica à raça e gênero. Os autores analisaram dados de dois líderes educacionais de ascendência mexicana em EUA: um director de um K-6 escola latina e no outro, diretor do faculdade chicana. Os resultados mostram traços de identidade positiva de líderes, que permite a implementação de uma liderança justa e socialmente justa entre os participantes do estudo. Estes resultados são novos e particularmente relevante em os EUA e outros países onde vivem um elevado número de descendentes de latinos e mexicanos. As estratégias empregadas pelos participantes sugerem formas alternativas de liderança não considerado ou pesquisa ou literatura. Os autores discutem as evidências encontradas que definem a teoria emergente de liderança crítica aplicada (ACL). Finalmente, orientações para a aplicação em diferentes contextos são fornecido

Electrochemical evaluation of the de-/re-activation of oxygen evolving Ir oxide

Understanding the influence of dynamic and stationary polarization on the deactivation of state-of-the-art IrOx catalysts is imperative for the design and operation of robust and efficient proton exchange membrane water electrolyzers. In this work, the deactivation and activity regeneration of a commercial IrOx catalyst investigated under potentiodynamic and potentiostatic conditions in acidic media by means of rotating disk electrode and electrogravimetry. Systematic electrochemical protocols were designed to decouple reversible from irreversible activity losses. Cyclic voltammetry provided a metric of the active surface area and traced the charge growth under different oxygen evolution reaction conditions. A direct logt dependent charge growth is observed, accompanied by the same fractional kinetic activity decay under potentiodynamic conditions. The loss is essentially recoverable after electrochemical reductive treatment, however at the expense of mild material dissolution. In contrast, extended potentiostatic operation induced irreversible intrinsic degradation after a critical time (0.5-1 h), accompanied by stability enhancement. This irreversible deactivation attributed to a gradual transformation of the hydrated IrOx to a dehydrated condensed oxide. Our results suggest that Ir dissolution during the regenerative treatment is not prohibitive, as long as the low potential modulations are not frequent