42 research outputs found
Gapless Excitation above a Domain Wall Ground State in a Flat Band Hubbard Model
We construct a set of exact ground states with a localized ferromagnetic
domain wall and with an extended spiral structure in a deformed flat-band
Hubbard model in arbitrary dimensions. We show the uniqueness of the ground
state for the half-filled lowest band in a fixed magnetization subspace. The
ground states with these structures are degenerate with all-spin-up or
all-spin-down states under the open boundary condition. We represent a spin
one-point function in terms of local electron number density, and find the
domain wall structure in our model. We show the existence of gapless
excitations above a domain wall ground state in dimensions higher than one. On
the other hand, under the periodic boundary condition, the ground state is the
all-spin-up or all-spin-down state. We show that the spin-wave excitation above
the all-spin-up or -down state has an energy gap because of the anisotropy.Comment: 26 pages, 1 figure. Typos are fixe
Ferromagnetic Domain Wall Ground States in One-Dimensional Deformed Flat-Band Hubbard Model
We construct a set of exact ground states with a localized ferromagnetic
domain wall and an extended spiral structure in a quasi-one-dimensional
deformed flat-band Hubbard model. In the case of quarter filling, we show the
uniqueness of the ground state with a fixed magnetization. The ground states
with these structures are degenerate with the all-spin-up and all-spin-down
states. This property of the degeneracy is the same as the domain wall
solutions in the XXZ Heisenberg-Ising model. We derive a useful recursion
relation for the normalization of the domain wall ground state. Using this
recursion relation, we discuss the convergence of the ground state expectation
values of arbitrary local operators in the infinite-volume limit. In the ground
state of the infinite-volume system, the translational symmetry is
spontaneously broken by this structure. We prove that the cluster property
holds for the domain wall ground state and excited states. We also estimate
bounds of the ground state expectation values of several observables, such as
one- and two-point functions of spin and electron number density.Comment: 34 pages, 3 figures, to be published in J. Stat. Phy
Activin E Controls Energy Homeostasis in Both Brown and White Adipose Tissues as a Hepatokine
Brown adipocyte activation or beige adipocyte emergence in white adipose tissue (WAT) increases energy expenditure, leading to a reduction in body fat mass and improved glucose metabolism. We found that activin E functions as a hepatokine that enhances thermogenesis in response to cold exposure through beige adipocyte emergence in inguinal WAT (ingWAT). Hepatic activin E overexpression activated thermogenesis through Ucp1 upregulation in ingWAT and other adipose tissues including interscapular brown adipose tissue and mesenteric WAT. Hepatic activin E-transgenic mice exhibited improved insulin sensitivity. Inhibin βE gene silencing inhibited cold-induced Ucp1 induction in ingWAT. Furthermore, in vitro experiments suggested that activin E directly stimulated expression of Ucp1 and Fgf21, which was mediated by transforming growth factor-β or activin type I receptors. We uncovered a function of activin E to stimulate energy expenditure through brown and beige adipocyte activation, suggesting a possible preventive or therapeutic target for obesity
Moments of vicious walkers and M\"obius graph expansions
A system of Brownian motions in one-dimension all started from the origin and
conditioned never to collide with each other in a given finite time-interval
is studied. The spatial distribution of such vicious walkers can be
described by using the repulsive eigenvalue-statistics of random Hermitian
matrices and it was shown that the present vicious walker model exhibits a
transition from the Gaussian unitary ensemble (GUE) statistics to the Gaussian
orthogonal ensemble (GOE) statistics as the time is going on from 0 to .
In the present paper, we characterize this GUE-to-GOE transition by presenting
the graphical expansion formula for the moments of positions of vicious
walkers. In the GUE limit , only the ribbon graphs contribute and the
problem is reduced to the classification of orientable surfaces by genus.
Following the time evolution of the vicious walkers, however, the graphs with
twisted ribbons, called M\"obius graphs, increase their contribution to our
expansion formula, and we have to deal with the topology of non-orientable
surfaces. Application of the recent exact result of dynamical correlation
functions yields closed expressions for the coefficients in the M\"obius
expansion using the Stirling numbers of the first kind.Comment: REVTeX4, 11 pages, 1 figure. v.2: calculations of the Green function
and references added. v.3: minor additions and corrections made for
publication in Phys.Rev.