125 research outputs found
Dynamical Friction in Gravitational Atoms
Due to superradiant instabilities, clouds of ultralight bosons can
spontaneously grow around rotating black holes, creating so-called
"gravitational atoms". In this work, we study their dynamical effects on binary
systems. We first focus on open orbits, showing that the presence of a cloud
can increase the cross section for the dynamical capture of a compact object by
more than an order of magnitude. We then consider closed orbits and demonstrate
that the backreaction of the cloud's ionization on the orbital motion should be
identified as dynamical friction. Finally, we study for the first time
eccentric and inclined orbits. We find that, while ionization quickly
circularizes the binary, it barely affects the inclination angle. These results
enable a more realistic description of the dynamics of gravitational atoms in
binaries and pave the way for dedicated searches with future gravitational wave
detectors.Comment: 36 pages, 13 figure
Superradiance: Axionic Couplings and Plasma Effects
Spinning black holes can transfer a significant fraction of their energy to
ultralight bosonic fields via superradiance, condensing them in a co-rotating
structure or "cloud". This mechanism turns black holes into powerful particle
detectors for bosons with extremely feeble interactions. To explore its full
potential, the couplings between such particles and the Maxwell field in the
presence of plasma need to be understood. In this work, we study these
couplings using numerical relativity. We first focus on the coupled
axion-Maxwell system evolving on a black hole background. By taking into
account the axionic coupling concurrently with the growth of the cloud, we
observe for the first time that a new stage emerges: that of a stationary state
where a constant flux of electromagnetic waves is fed by superradiance, for
which we find accurate analytical estimates. Moreover, we show that the
existence of electromagnetic instabilities in the presence of plasma is
entirely controlled by the axionic coupling; even for dense plasmas, an
instability is triggered for high enough couplings.Comment: 32 pages, 23 figure
Disks, spikes, and clouds: distinguishing environmental effects on BBH gravitational waveforms
Future gravitational wave interferometers such as LISA, Taiji, DECIGO, and
TianQin, will enable precision studies of the environment surrounding black
holes. In this paper, we study intermediate and extreme mass ratio binary black
hole inspirals, and consider three possible environments surrounding the
primary black hole: accretion disks, dark matter spikes, and clouds of
ultra-light scalar fields, also known as gravitational atoms. We present a
Bayesian analysis of the detectability and measurability of these three
environments. Focusing for concreteness on the case of a detection with LISA,
we show that the characteristic imprint they leave on the gravitational
waveform would allow us to identify the environment that generated the signal,
and to accurately reconstruct its model parameters.Comment: 8 pages, 4 figures, 2 tables plus appendice
On structural properties of the value function for an unbounded jump Markov process with an application to a processor sharing retrial queue
The derivation of structural properties for unbounded jump Markov processes cannot be done using standard mathematical tools, since the analysis is hindered due to the fact that the system is not uniformizable. We present a promising technique, a smoothed rate truncation method, to overcome the limitations of standard techniques and allow for the derivation of structural properties. We introduce this technique by application to a processor sharing queue with impatient customers that can retry if they renege. We are interested in structural properties of the value function of the system as a function of the arrival rate
Comparing league formats with respect to match importance in Belgian football
Recently, most clubs in the highest Belgian football division have become convinced that the format of their league should be changed. Moreover, the TV station that broadcasts the league is pleading for a more attractive competition. However, the clubs have not been able to agree on a new league format, mainly because they have conflicting interests. In this paper, we compare the current league format, and three other formats that have been considered by the Royal Belgian Football Association. We simulate the course of each of these league formats, based on historical match results. We assume that the attractiveness of a format is determined by the importance of its games; our importance measure for a game is based on the number of teams for which this game can be decisive to reach a given goal. Furthermore, we provide an overview of how each league format aligns with the expectations and interests of each type of club
Random multi-index matching problems
The multi-index matching problem (MIMP) generalizes the well known matching
problem by going from pairs to d-uplets. We use the cavity method from
statistical physics to analyze its properties when the costs of the d-uplets
are random. At low temperatures we find for d>2 a frozen glassy phase with
vanishing entropy. We also investigate some properties of small samples by
enumerating the lowest cost matchings to compare with our theoretical
predictions.Comment: 22 pages, 16 figure
Types of Artemisia pollen season depending on the weather conditions in Wrocław (Poland), 2002–2011
Prediction of the birch pollen season characteristics in Cracow, Poland using an 18-year data series
Nonzero-sum Stochastic Games
This paper treats of stochastic games. We focus on nonzero-sum games and provide a detailed survey of
selected recent results. In Section 1, we consider stochastic Markov games. A correlation of strategies of the players, involving ``public signals'', is described, and a correlated equilibrium theorem proved recently by Nowak and Raghavan for discounted stochastic games with general state space is presented. We also report an extension of this result to a class of undiscounted stochastic games, satisfying some uniform ergodicity condition.
Stopping games are related to stochastic Markov games. In
Section 2, we describe a version of Dynkin's game related to
observation of a Markov process with random assignment mechanism of states to the players. Some recent contributions of the second author in this area are reported. The paper also contains a brief overview of the theory of nonzero-sum stochastic games and stopping games which is very far from being complete
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