4,729 research outputs found
Stopping in central Pb + Pb collisions at SPS energies and beyond
We investigate stopping and baryon transport in central relativistic Pb + Pb
and Au + Au collisions. At energies reached at the CERN Super Proton
Synchrotron [sqrt(s_NN) = 6.3-17.3 GeV] and at RHIC (62.4 GeV), we determine
the fragmentation-peak positions from the data. The resulting linear growth of
the peak positions with beam rapidity is in agreement with our results from a
QCD-based approach that accounts for gluon saturation. No discontinuities in
the net-proton fragmentation peak positions occur in the expected transition
region from partons to hadrons at 6-10 GeV.Comment: 5 pages, 3 figures, 1 table. Figures updated, table shortened, 1
reference adde
Universal four-body states in heavy-light mixtures with positive scattering length
The number of four-body states known to behave universally is small. This
work adds a new class of four-body states to this relatively short list. We
predict the existence of a universal four-body bound state for heavy-light
mixtures consisting of three identical heavy fermions and a fourth
distinguishable lighter particle with mass ratio and
short-range interspecies interaction characterized by a positive s-wave
scattering length. The structural properties of these universal states are
discussed and finite-range effects are analyzed. The bound states can be
experimentally realized and probed utilizing ultracold atom mixtures.Comment: 5 page
Constructive Decision Theory
Contemporary approaches to decision making describe a decision problem by sets of states and outcomes, and a rich set of acts: functions from states to outcomes over which the decision maker (DM) has preferences. Real problems do not come so equipped. It is often unclear what the state and outcome spaces would be. We present an alternative foundation for decision making, in which the primitive objects of choice are syntactic programs. We show that if the DM's preference relation on objects of choice satisfies appropriate axioms, then we can find states, outcomes, and an embedding of the programs into Savage acts such that preferences can be represented by EU in the Savage framework. A modeler can test for SEU behavior without having access to the subjective states and outcomes. We illustrate the power of our approach by showing that it can represent DMs who are subject to framing effects.Decision theory, subjective expected utility, behavioral anomalies
Effective renormalized multi-body interactions of harmonically confined ultracold neutral bosons
We calculate the renormalized effective 2-, 3-, and 4-body interactions for N
neutral ultracold bosons in the ground state of an isotropic harmonic trap,
assuming 2-body interactions modeled with the combination of a zero-range and
energy-dependent pseudopotential. We work to third-order in the scattering
length a defined at zero collision energy, which is necessary to obtain both
the leading-order effective 4-body interaction and consistently include
finite-range corrections for realistic 2-body interactions. The leading-order,
effective 3- and 4-body interaction energies are U3 = -(0.85576...)(a/l)^2 +
2.7921(1)(a/l)^3 + O[(a/l)^4] and U4 = +(2.43317...)(a/l)^3 + O[(a\l)^4], where
w and l are the harmonic oscillator frequency and length, respectively, and
energies are in units of hbar*w. The one-standard deviation error 0.0001 for
the third-order coefficient in U3 is due to numerical uncertainty in estimating
a slowly converging sum; the other two coefficients are either analytically or
numerically exact. The effective 3- and 4-body interactions can play an
important role in the dynamics of tightly confined and strongly correlated
systems. We also performed numerical simulations for a finite-range boson-boson
potential, and it was comparison to the zero-range predictions which revealed
that finite-range effects must be taken into account for a realistic
third-order treatment. In particular, we show that the energy-dependent
pseudopotential accurately captures, through third order, the finite-range
physics, and in combination with the multi-body effective interactions gives
excellent agreement with the numerical simulations, validating our theoretical
analysis and predictions.Comment: Updated introduction, correction of a few typos and sign error
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