15,994 research outputs found
The Invariant Measure of Random Walks in the Quarter-plane: Representation in Geometric Terms
We consider the invariant measure of homogeneous random walks in the
quarter-plane. In particular, we consider measures that can be expressed as a
finite linear combination of geometric terms and present conditions on the
structure of these linear combinations such that the resulting measure may
yield an invariant measure of a random walk. We demonstrate that each geometric
term must individually satisfy the balance equations in the interior of the
state space and further show that the geometric terms in an invariant measure
must have a pairwise-coupled structure. Finally, we show that at least one of
the coefficients in the linear combination must be negative
The invariant measure of homogeneous Markov processes in the quarter-plane: Representation in geometric terms
We consider the invariant measure of a homogeneous continuous-time Markov process in the quarter-plane. The basic solutions of the global balance equation are the geometric distributions. We first show that the invariant measure can not be a finite linear combination of basic geometric distributions, unless it consists of a single basic geometric distribution. Second, we show that a countable linear combination of geometric terms can be an invariant measure only if it consists of pairwise-coupled terms. As a consequence, we obtain a complete characterization of all countable linear combinations of geometric distributions that may yield an invariant measure for a homogeneous continuous-time Markov process in the quarter-plane
Altruism, Cooperation, and Efficiency: Agricultural Production in Polygynous Households
Altruism among family members can, in some cases, inhibit cooperation by increasing the utility that players expect to receive in a non-cooperative equilibrium. To test this, we examine agricultural productivity in polygynous households in West Africa. We find that cooperation is greater – production is more efficient – among co-wives than among husbands and wives because co-wives are less altruistic towards each other. The results are not driven by scale effects or self-selection into polygyny. Nor can they be explained by greater propensity for cooperation among women generally or by the household head acting as an enforcement mechanism for others' cooperative agreements.altruism, non-cooperative behavior, household bargaining, polygyny, Africa
Power Corrections to the Universal Heavy WIMP-Nucleon Cross Section
WIMP-nucleon scattering is analyzed at order in Heavy WIMP Effective
Theory. The power corrections, where is the WIMP mass,
distinguish between different underlying UV models with the same universal
limit and their impact on direct detection rates can be enhanced relative to
naive expectations due to generic amplitude-level cancellations at leading
order. The necessary one- and two-loop matching calculations onto the
low-energy effective theory for WIMP interactions with Standard Model quarks
and gluons are performed for the case of an electroweak SU(2) triplet WIMP,
considering both the cases of elementary fermions and composite scalars. The
low-velocity WIMP-nucleon scattering cross section is evaluated and compared
with current experimental limits and projected future sensitivities. Our
results provide the most robust prediction for electroweak triplet Majorana
fermion dark matter direct detection rates; for this case, a cancellation
between two sources of power corrections yields a small total correction,
and a total cross section close to the universal limit for . For the SU(2) composite scalar, the corrections
introduce dependence on underlying strong dynamics. Using a leading chiral
logarithm evaluation, the total correction has a larger magnitude and
uncertainty than in the fermionic case, with a sign that further suppresses the
total cross section. These examples provide definite targets for future direct
detection experiments and motivate large scale detectors capable of probing to
the neutrino floor in the TeV mass regime.Comment: 12 pages, 4 figures; references added, XENONnT projection included,
version to appear in Physics Letters
- …