848 research outputs found
In the beginning was game semantics
This article presents an overview of computability logic -- the
game-semantically constructed logic of interactive computational tasks and
resources. There is only one non-overview, technical section in it, devoted to
a proof of the soundness of affine logic with respect to the semantics of
computability logic. A comprehensive online source on the subject can be found
at http://www.cis.upenn.edu/~giorgi/cl.htmlComment: To appear in: "Games: Unifying Logic, Language and Philosophy". O.
Majer, A.-V. Pietarinen and T. Tulenheimo, eds. Springer Verlag, Berli
Perturbative Approach For Non Renormalizable Theories
Renormalization procedure is generalized to be applicable for non
renormalizable theories. It is shown that introduction of an extra expansion
parameter allows to get rid of divergences and express physical quantities as
series of finite number of interdependent expansion parameters. Suggested
method is applied to quantum (Einstein's) gravity.Comment: 14 pages (LaTEX file
Magnetization plateau in the S=1/2 spin ladder with alternating rung exchange
We have studied the ground state phase diagram of a spin ladder with
alternating rung exchange in
a magnetic filed, in the limit where the rung coupling is dominant. In this
limit the model is mapped onto an Heisenberg chain in a uniform and
staggered longitudinal magnetic fields, where the amplitude of the staggered
field is . We have shown that the magnetization curve of the
system exhibits a plateau at magnetization equal to the half of the saturation
value. The width of a plateau scales as , where in the
case of ladder with isotropic antiferromagnetic legs and in the case
of ladder with isotropic ferromagnetic legs. We have calculated four critical
fields ( and ) corresponding to transitions between
different magnetic phases of the system. We have shown that these transitions
belong to the universality class of the commensurate-incommensurate transition.Comment: 6 pages, 2 figure
Band-Insulator-Metal-Mott-Insulator transition in the half--filled ionic-Hubbard chain
We investigate the ground state phase diagram of the half-filled
repulsive Hubbard model in the presence of a staggered ionic
potential , using the continuum-limit bosonization approach. We find,
that with increasing on-site-repulsion , depending on the value of the
next-nearest-hopping amplitude , the model shows three different
versions of the ground state phase diagram. For , the ground state phase diagram consists of the following
three insulating phases: Band-Insulator at , Ferroelectric Insulator
at . For
there is only one transition from a spin gapped
metallic phase at .
Finally, for intermediate values of the next-nearest-hopping amplitude
we find that with increasing
on-site repulsion, at the model undergoes a second-order
commensurate-incommensurate type transition from a band insulator into a
metallic state and at larger there is a Kosterlitz-Thouless type
transition from a metal into a ferroelectric insulator.Comment: 9 pages 3 figure
General properties of phase diagrams of heavy-fermion metals
We study the temperature-magnetic field T-B phase diagrams of heavy fermion
(HF) metals, and show that at sufficiently high temperatures outside the
ordered phase the crossover temperature T*(B), regarded as the energy scale,
follows a linear B-dependence, crossing the origin of the T-B phase diagram.
This behavior of T*(B) constitutes the general property, and is formed by the
presence of fermion condensation quantum phase transition hidden within the
ordered phase. Our result is in good agreement with the experimental T-B phase
diagram of the HF metals YbRh2Si2, Yb(Rh{0.93}Co{0.07})2Si2, and
Yb(Rh{0.94}Ir{0.06})2Si2. To support our observations, we analyze the
isothermal magnetization M, and demonstrate that dM/dT exhibits a universal
temperature behavior over magnetic field scaling. The obtained results are in
good agreement with the corresponding data collected on YbRh2Si2 as a function
of magnetic field at different temperatures under hydrostatic pressure.Comment: 6 pages, 6 figures. arXiv admin note: substantial text overlap with
arXiv:1311.062
Heat transport in magnetic fields by quantum spin liquid in the organic insulators EtMe3Sb[Pd(dmit)2]2 and \kappa-(BEDT-TTF)2Cu2(CN)3
Measurements of the low-temperature thermal conductivity collected on
insulators with geometrical frustration produce important experimental facts
shedding light on the nature of quantum spin liquid composed of spinons. We
employ a model of strongly correlated quantum spin liquid located near the
fermion condensation phase transition to analyze the exciting measurements of
the low-temperature thermal conductivity in magnetic fields collected on the
organic insulators EtMe3Sb[Pd(dmit)_2]2 and \kappa-(BEDT-TTF)2Cu2(CN)3. Our
analysis of the conductivity allows us to reveal a strong dependence of the
effective mass of spinons on magnetic fields, to detect a scaling behavior of
the conductivity, and to relate it to both the spin-lattice relaxation rate and
the magnetoresistivity. Our calculations and observations are in a good
agreement with experimental data.Comment: 6 pages, 4 figure
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