2,437 research outputs found
Generalized Indiscernibles as Model-complete Theories
We give an almost entirely model-theoretic account of both Ramsey classes of
finite structures and of generalized indiscernibles as studied in special cases
in (for example) [7], [9]. We understand "theories of indiscernibles" to be
special kinds of companionable theories of finite structures, and much of the
work in our arguments is carried in the context of the model-companion. Among
other things, this approach allows us to prove that the companion of a theory
of indiscernibles whose "base" consists of the quantifier-free formulas is
necessarily the theory of the Fraisse limit of a Fraisse class of linearly
ordered finite structures (where the linear order will be at least
quantifier-free definable). We also provide streamlined arguments for the
result of [6] identifying extremely amenable groups with the automorphism
groups of limits of Ramsey classes.Comment: 21 page
Holographic entropy of Warped-AdS black holes
We study the asymptotic symmetries of three-dimensional Warped Anti-de Sitter
(WAdS) spaces in three-dimensional New Massive Gravity (NMG). For a specific
choice of asymptotic boundary conditions, we find that the algebra of charges
is infinite-dimensional and coincides with the semidirect sum of Virasoro
algebra with non-vanishing central charge and an affine
Ka\v{c}-Moody algebra. We show that the WAdS black hole configurations organize
in terms of two commuting Virasoro algebras. We identify the Virasoro
generators that expand the associated representations in the dual Warped
Conformal Field Theory (WCFT) and, by applying the Warped version of the Cardy
formula, we prove that the microscopic WCFT computation exactly reproduces the
entropy of black holes in WAdS space.Comment: 13 pages. v2 minor typos correcte
A monthly monetary model with banking intermediation for the euro area
JEL Classification: C32, E41, E43, E50, G21Banking intermediation, cointegration, Loan demand, Money demand, Structural VECM
Understanding recurrent crime as system-immanent collective behavior
Containing the spreading of crime is a major challenge for society. Yet,
since thousands of years, no effective strategy has been found to overcome
crime. To the contrary, empirical evidence shows that crime is recurrent, a
fact that is not captured well by rational choice theories of crime. According
to these, strong enough punishment should prevent crime from happening. To gain
a better understanding of the relationship between crime and punishment, we
consider that the latter requires prior discovery of illicit behavior and study
a spatial version of the inspection game. Simulations reveal the spontaneous
emergence of cyclic dominance between ''criminals'', ''inspectors'', and
''ordinary people'' as a consequence of spatial interactions. Such cycles
dominate the evolutionary process, in particular when the temptation to commit
crime or the cost of inspection are low or moderate. Yet, there are also
critical parameter values beyond which cycles cease to exist and the population
is dominated either by a stable mixture of criminals and inspectors or one of
these two strategies alone. Both continuous and discontinuous phase transitions
to different final states are possible, indicating that successful strategies
to contain crime can be very much counter-intuitive and complex. Our results
demonstrate that spatial interactions are crucial for the evolutionary outcome
of the inspection game, and they also reveal why criminal behavior is likely to
be recurrent rather than evolving towards an equilibrium with monotonous
parameter dependencies.Comment: 9 two-column pages, 5 figures; accepted for publication in PLoS ON
Asymptotic symmetries and dynamics of three-dimensional flat supergravity
A consistent set of asymptotic conditions for the simplest supergravity
theory without cosmological constant in three dimensions is proposed. The
canonical generators associated to the asymptotic symmetries are shown to span
a supersymmetric extension of the BMS algebra with an appropriate central
charge. The energy is manifestly bounded from below with the ground state given
by the null orbifold or Minkowski spacetime for periodic, respectively
antiperiodic boundary conditions on the gravitino. These results are related to
the corresponding ones in AdS supergravity by a suitable flat limit. The
analysis is generalized to the case of minimal flat supergravity with
additional parity odd terms for which the Poisson algebra of canonical
generators form a representation of the super-BMS algebra with an
additional central charge.Comment: 13 pages, no figure
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