27,391 research outputs found
On spectral hypergraph theory of the adjacency tensor
We study both and -eigenvalues of the adjacency tensor of a uniform
multi-hypergraph and give conditions for which the largest positive or
-eigenvalue corresponds to a strictly positive eigenvector. We also
investigate when the -spectrum of the adjacency tensor is symmetric
Toward a Theory of Marginally Efficient Markets
Empirical evidence suggests that even the most competitive markets are not
strictly efficient. Price histories can be used to predict near future returns
with a probability better than random chance. Many markets can be considered as
{\it favorable games}, in the sense that there is a small probabilistic edge
that smart speculators can exploit. We propose to identify this probability
using conditional entropy concept. A perfect random walk has this entropy
maximized, and departure from the maximal value represents a price history's
predictability. We propose that market participants should be divided into two
categories: producers and speculators. The former provides the negative entropy
into the price, upon which the latter feed. We show that the residual negative
entropy can never be arbitraged away: infinite arbitrage capital is needed to
make the price a perfect random walk.Comment: 9 pages, 3 ps figure
Thermal Spin-Transfer Torques in Magnetoelectronic Devices
We predict that the magnetization direction of a ferromagnet can be reversed
by the spin-transfer torque accompanying spin-polarized thermoelectric heat
currents. We illustrate the concept by applying a finite-element theory of
thermoelectric transport in disordered magnetoelectronic circuits and devices
to metallic spin valves. When thermalization is not complete, a spin heat
accumulation vector is found in the normal metal spacer, i.e., a directional
imbalance in the temperature of majority and minority spins.Comment: Accepted for publication by Physical Review Letter
Dark Matter and Neutrino Mass from the Smallest Non-Abelian Chiral Dark Sector
All pieces of concrete evidence for phenomena outside the standard model (SM)
- neutrino masses and dark matter - are consistent with the existence of new
degrees of freedom that interact very weakly, if at all, with those in the SM.
We propose that these new degrees of freedom organize themselves into a simple
dark sector, a chiral SU(3) x SU(2) gauge theory with the smallest nontrivial
fermion content. Similar to the SM, the dark SU(2) is spontaneously broken
while the dark SU(3) confines at low energies. At the renormalizable level, the
dark sector contains massless fermions - dark leptons - and stable massive
particles - dark protons. We find that dark protons with masses between 10-100
TeV satisfy all current cosmological and astrophysical observations concerning
dark matter even if dark protons are a symmetric thermal relic. The dark
leptons play the role of right-handed neutrinos and allow simple realizations
of the seesaw mechanism or the possibility that neutrinos are Dirac fermions.
In the latter case, neutrino masses are also parametrically different from
charged-fermion masses and the lightest neutrino is predicted to be massless.
Since the new "neutrino" and "dark matter" degrees of freedom interact with one
another, these two new-physics phenomena are intertwined. Dark leptons play a
nontrivial role in early universe cosmology while indirect searches for dark
matter involve, decisively, dark matter annihilations into dark leptons. These,
in turn, may lead to observable signatures at high-energy neutrino and
gamma-ray observatories, especially once one accounts for the potential
Sommerfeld enhancement of the annihilation cross-section, derived from the
low-energy dark-sector effective theory, a possibility we explore
quantitatively in some detail.Comment: 35 pages, 7 figures. Matches published versio
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