32,094 research outputs found
Superradiance in rotating stars and pulsar-timing constraints on dark photons
In the presence of massive bosonic degrees of freedom, rotational
superradiance can trigger an instability that spins down black holes. This
leads to peculiar gravitational-wave signatures and distribution in the
spin-mass plane, which in turn can impose stringent constraints on ultralight
fields. Here, we demonstrate that there is an analogous spindown effect for
conducting stars. We show that rotating stars amplify low frequency
electromagnetic waves, and that this effect is largest when the time scale for
conduction within the star is of the order of a light crossing time. This has
interesting consequences for dark photons, as massive dark photons would cause
stars to spin down due to superradiant instabilities. The time scale of the
spindown depends on the mass of the dark photon, and on the rotation rate,
compactness, and conductivity of the star. Existing measurements of the
spindown rate of pulsars place direct constraints on models of dark sectors.
Our analysis suggests that dark photons of mass eV are
excluded by pulsar-timing observations. These constraints also exclude
superradiant instabilities triggered by dark photons as an explanation for the
spin limit of observed pulsars.Comment: 13 pages, 4 figure
Collider Searches for Long-Lived Particles Beyond the Standard Model
Experimental tests of the Standard Model of particle physics (SM) find
excellent agreement with its predictions. Since the original formation of the
SM, experiments have provided little guidance regarding the explanations of
phenomena outside the SM, such as the baryon asymmetry and dark matter. Nor
have we understood the aesthetic and theoretical problems of the SM, despite
years of searching for physics beyond the Standard Model (BSM) at particle
colliders. Some BSM particles can be produced at colliders yet evade being
discovered, if the reconstruction and analysis procedures not matched to
characteristics of the particle. An example is particles with large lifetimes.
As interest in searches for such long-lived particles (LLPs) grows rapidly, a
review of the topic is presented in this article. The broad range of
theoretical motivations for LLPs and the experimental strategies and methods
employed to search for them are described. Results from decades of LLP searches
are reviewed, as are opportunities for the next generation of searches at both
existing and future experiments.Comment: 79 pages, 36 figures, submitted to Progress in Particle and Nuclear
Physic
Catalytic ignition model in a monolithic reactor with in-depth reaction
Two transient models have been developed to study the catalytic ignition in a monolithic catalytic reactor. The special feature in these models is the inclusion of thermal and species structures in the porous catalytic layer. There are many time scales involved in the catalytic ignition problem, and these two models are developed with different time scales. In the full transient model, the equations are non-dimensionalized by the shortest time scale (mass diffusion across the catalytic layer). It is therefore accurate but is computationally costly. In the energy-integral model, only the slowest process (solid heat-up) is taken as nonsteady. It is approximate but computationally efficient. In the computations performed, the catalyst is platinum and the reactants are rich mixtures of hydrogen and oxygen. One-step global chemical reaction rates are used for both gas-phase homogeneous reaction and catalytic heterogeneous reaction. The computed results reveal the transient ignition processes in detail, including the structure variation with time in the reactive catalytic layer. An ignition map using reactor length and catalyst loading is constructed. The comparison of computed results between the two transient models verifies the applicability of the energy-integral model when the time is greater than the second largest time scale of the system. It also suggests that a proper combined use of the two models can catch all the transient phenomena while minimizing the computational cost
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