3,223 research outputs found
Random matrix theory of unquenched two-colour QCD with nonzero chemical potential
We solve a random two-matrix model with two real asymmetric matrices whose
primary purpose is to describe certain aspects of quantum chromodynamics with
two colours and dynamical fermions at nonzero quark chemical potential mu. In
this symmetry class the determinant of the Dirac operator is real but not
necessarily positive. Despite this sign problem the unquenched matrix model
remains completely solvable and provides detailed predictions for the Dirac
operator spectrum in two different physical scenarios/limits: (i) the
epsilon-regime of chiral perturbation theory at small mu, where mu^2 multiplied
by the volume remains fixed in the infinite-volume limit and (ii) the
high-density regime where a BCS gap is formed and mu is unscaled. We give
explicit examples for the complex, real, and imaginary eigenvalue densities
including Nf=2 non-degenerate flavours. Whilst the limit of two degenerate
masses has no sign problem and can be tested with standard lattice techniques,
we analyse the severity of the sign problem for non-degenerate masses as a
function of the mass split and of mu.
On the mathematical side our new results include an analytical formula for
the spectral density of real Wishart eigenvalues in the limit (i) of weak
non-Hermiticity, thus completing the previous solution of the corresponding
quenched model of two real asymmetric Wishart matrices.Comment: 45 pages, 31 figures; references added, as published in JHE
Cosmological perturbation theory
This is a review on cosmological perturbation theory. After an introduction,
it presents the problem of gauge transformation. Gauge invariant variables are
introduced and the Einstein and conservation equations are written in terms of
these variables. Some examples, especially perfect fluids and scalar fields are
presented in detail. The generation of perturbations during inflation is
studied. Lightlike geodesics and their relevance for CMB anisotropies are
briefly discussed. Perturbation theory in braneworlds is also introduced.Comment: my course at the Second Aegean Summerschool on the Early Universe, 39
pages (I have corrected some typos
A small and light weight heat exchanger for on-board helium refrigerator
A small and light weight heat exchanger used for small helium refrigerator has been developed by Sumitomo Heavy Industries, Ltd. This heat exchanger is a laminated metal heat exchanger which consists of perforated aluminum metal plates and glassfiber reinforced plastic separators. The size is from 100 mm to 28 mm in diameter and about 300 mm in length. The weight is from 2.5 kg to 0.6 kg. Also it can be used between room temperature and liquid helium temperature. The thermal efficiency obtained has been more than 96%. The heat exchanger has been practically used for on-board helium refrigerator in Japanese National Railways' superconducting magnetic levitated trains
Double inflation in supergravity and the primordial black hole formation
We study a double inflation model (a hybrid inflation + a new inflation) in
supergravity and discuss the formation of primordial black holes (PBHs) with
mass \sim 10^{-20}-10^{5}M_{\odot}. We find that in a wide range of parameter
space, we obtain PBHs which amount to \Omega \simeq 1, i.e., PBH dark matter.
Also, we find a set of inflation parameters which produces PBHs evaporating
now. Those PBHs may be responsible for antiproton fluxes observed by the BESS
experiment.Comment: 14 pages, 2 figures (RevTeX file
Politics and eminent domain: Evidence from the 1879 California Constitution
This paper explores the politics of eminent domain, using a specific historical episode: the enactment of the new California constitution in 1879. It presents evidence that the failure of a constitutional provision that would have codified eminent domain powers for water development resulted from a complex interchange of economic interests among farmers, miners, and urban residents. This evidence was manifested in delegate behavior on the floor of the constitutional convention in 1878, including various roll-call votes, which are subjected to an econometric analysis. The results have implications for the interpretation of legislative eminent domain decisions, and the degree to which economic development processes are shaped by the institutional environment in which they occur
Judicial Deference and the Efficiency of the Common Law
Economists and legal scholars in the law-and-economics tradition have long been occupied with the question of whether, and the extent to which, the common law is efficient. There have been two main approaches taken in the scholarly literature. One approach has been to focus on judges, who are modeled having various motivations including, but not necessarily confined to, concern for efficient allocation of resources.1 However, to the extent they are concerned with efficiency, this attitude will be reflected in their opinions.2 This argument has been subject to criticism by scholars on various grounds, including questioning the assumption that judges are principally interested in promoting efficient resource use, at the expense of other arguments in their utility function such as ideology, fairness, and professional reputation and status
Transaction Costs in Water Transfers: The issue of local control
As water becomes increasingly scarce relative to demand, it becomes increasingly important to maximize the value that we derive from it. For years, economists have been advocating increased reliance on water markets as a means of rationalizing water use, the objective being to facilitate the allocation of water to its highest-value uses.1
Yet in many parts of the arid West, water markets have been surprisingly slow to take hold. Despite some recent progress, perhaps nowhere is this truer than in California.2 The conditions of extreme drought recently experienced by the state make it even more incumbent to better understand why water markets have been so slow to emerge
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