892 research outputs found
Future Foam
We study pocket universes which have zero cosmological constant and
non-trivial boundary topology. These arise from bubble collisions in eternal
inflation. Using a simplified dust model of collisions we find that boundaries
of any genus can occur. Using a radiation shell model we perform analytic
studies in the thin wall limit to show the existence of geometries with a
single toroidal boundary. We give plausibility arguments that higher genus
boundaries can also occur. In geometries with one boundary of any genus a
timelike observer can see the entire boundary. Geometries with multiple
disconnected boundaries can also occur. In the spherical case with two
boundaries the boundaries are separated by a horizon. Our results suggest that
the holographic dual description for eternal inflation, proposed by Freivogel,
Sekino, Susskind and Yeh, should include summation over the genus of the base
space of the dual conformal field theory. We point out peculiarities of this
genus expansion compared to the string perturbation series.Comment: 23 pages, 6 figure
Occurrence of an Ocean Sunfish (Mola mola) Larva in the Florida Current
During a yearlong ichthyoplankton survey conducted in the Florida Current, a single ocean sunfish, Mola mola, was found from the 284 samples and 1,454 identified specimens. This sunfish larva is one of only 17 on record from the Gulf of Mexico and northwest Atlantic
Comment on ``Inflation and flat directions in modular invariant superstring effective theories''
The inflation model of Gaillard, Lyth and Murayama is revisited, with a
systematic scan of the parameter space for dilaton stabilization during
inflation.Comment: 7 pages, 2 figure
A Renormalization Group for Hamiltonians: Numerical Results
We describe a renormalization group transformation that is related to the
breakup of golden invariant tori in Hamiltonian systems with two degrees of
freedom. This transformation applies to a large class of Hamiltonians, is
conceptually simple, and allows for accurate numerical computations. In a
numerical implementation, we find a nontrivial fixed point and determine the
corresponding critical index and scaling. Our computed values for various
universal constants are in good agreement with existing data for
area-preserving maps. We also discuss the flow associated with the nontrivial
fixed point.Comment: 11 Pages, 2 Figures. For future updates, check
ftp://ftp.ma.utexas.edu/pub/papers/koch
Understanding the current and future usage of donor human milk in hospitals: An online survey of UK neonatal units
The use of donor human milk (DHM) where there is a shortfall of maternal milk can benefit both infant and maternal outcomes but DHM supply is not always assured. This study aimed to understand current DHM usage in UK neonatal units and potential future demand to inform service planning. An online survey was disseminated to all UK neonatal units using Smart Survey or by telephone between February and April 2022 after development alongside neonatal unit teams. Surveys were completed by 55.4% of units (108/195) from all 13 Operational Delivery Networks. Only four units reported not using DHM, and another two units only if infants are transferred on DHM feeds. There was marked diversity in DHM implementation and usage and unit protocols varied greatly. Five of six units with their own milk bank had needed to source milk from an external milk bank in the last year. Ninety units (84.9%) considered DHM was sometimes (n = 35) or always (n = 55) supportive of maternal breastfeeding, and three units (2.9%) responded that DHM was rarely supportive of breastfeeding. Usage was predicted to increase by 37 units (34.9%), and this drive was principally a result of parental preference, clinical trials and improved evidence. These findings support the assumption that UK hospital DHM demand will increase after updated recommendations from the World Health Organization (WHO) and the British Association of Perinatal Medicine. These data will assist service delivery planning, underpinned by an ongoing programme of implementation science and training development, to ensure future equity of access to DHM nationally
The Cost of Stability in Coalitional Games
A key question in cooperative game theory is that of coalitional stability,
usually captured by the notion of the \emph{core}--the set of outcomes such
that no subgroup of players has an incentive to deviate. However, some
coalitional games have empty cores, and any outcome in such a game is unstable.
In this paper, we investigate the possibility of stabilizing a coalitional
game by using external payments. We consider a scenario where an external
party, which is interested in having the players work together, offers a
supplemental payment to the grand coalition (or, more generally, a particular
coalition structure). This payment is conditional on players not deviating from
their coalition(s). The sum of this payment plus the actual gains of the
coalition(s) may then be divided among the agents so as to promote stability.
We define the \emph{cost of stability (CoS)} as the minimal external payment
that stabilizes the game.
We provide general bounds on the cost of stability in several classes of
games, and explore its algorithmic properties. To develop a better intuition
for the concepts we introduce, we provide a detailed algorithmic study of the
cost of stability in weighted voting games, a simple but expressive class of
games which can model decision-making in political bodies, and cooperation in
multiagent settings. Finally, we extend our model and results to games with
coalition structures.Comment: 20 pages; will be presented at SAGT'0
Analytic Study for the String Theory Landscapes via Matrix Models
We demonstrate a first-principle analysis of the string theory landscapes in
the framework of non-critical string/matrix models. In particular, we discuss
non-perturbative instability, decay rate and the true vacuum of perturbative
string theories. As a simple example, we argue that the perturbative string
vacuum of pure gravity is stable; but that of Yang-Lee edge singularity is
inescapably a false vacuum. Surprisingly, most of perturbative minimal string
vacua are unstable, and their true vacuum mostly does not suffer from
non-perturbative ambiguity. Importantly, we observe that the instability of
these tachyon-less closed string theories is caused by ghost D-instantons (or
ghost ZZ-branes), the existence of which is determined only by non-perturbative
completion of string theory.Comment: v1: 5 pages, 2 figures; v2: references and footnote added; v3: 7
pages, 4 figures, organization changed, explanations expanded, references
added, reconstruction program from arbitrary spectral curves shown explicitl
M Theory As A Matrix Model: A Conjecture
We suggest and motivate a precise equivalence between uncompactified eleven
dimensional M-theory and the N = infinity limit of the supersymmetric matrix
quantum mechanics describing D0-branes. The evidence for the conjecture
consists of several correspondences between the two theories. As a consequence
of supersymmetry the simple matrix model is rich enough to describe the
properties of the entire Fock space of massless well separated particles of the
supergravity theory. In one particular kinematic situation the leading large
distance interaction of these particles is exactly described by supergravity .
The model appears to be a nonperturbative realization of the holographic
principle. The membrane states required by M-theory are contained as
excitations of the matrix model. The membrane world volume is a noncommutative
geometry embedded in a noncommutative spacetime.Comment: Typo and tex error corrected. 41 pages, harvma
Phases of Josephson Junction Ladders
We study a Josephson junction ladder in a magnetic field in the absence of
charging effects via a transfer matrix formalism. The eigenvalues of the
transfer matrix are found numerically, giving a determination of the different
phases of the ladder. The spatial periodicity of the ground state exhibits a
devil's staircase as a function of the magnetic flux filling factor . If the
transverse Josephson coupling is varied a continuous superconducting-normal
transition in the transverse direction is observed, analogous to the breakdown
of the KAM trajectories in dynamical systems.Comment: 12 pages with 3 figures, REVTE
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