497 research outputs found
Wheeler-DeWitt Equation in 3 + 1 Dimensions
Physical properties of the quantum gravitational vacuum state are explored by
solving a lattice version of the Wheeler-DeWitt equation. The constraint of
diffeomorphism invariance is strong enough to uniquely determine the structure
of the vacuum wave functional in the limit of infinitely fine triangulations of
the three-sphere. In the large fluctuation regime the nature of the wave
function solution is such that a physically acceptable ground state emerges,
with a finite non-perturbative correlation length naturally cutting off any
infrared divergences. The location of the critical point in Newton's constant
, separating the weak from the strong coupling phase, is obtained, and it
is inferred from the structure of the wave functional that fluctuations in the
curvatures become unbounded at this point. Investigations of the vacuum wave
functional further suggest that for weak enough coupling, , a
pathological ground state with no continuum limit appears, where configurations
with small curvature have vanishingly small probability. One is then lead to
the conclusion that the weak coupling, perturbative ground state of quantum
gravity is non-perturbatively unstable, and that gravitational screening cannot
be physically realized in the lattice theory. The results we find are in
general agreement with the Euclidean lattice gravity results, and lend further
support to the claim that the Lorentzian and Euclidean lattice formulations for
gravity describe the same underlying non-perturbative physics.Comment: 44 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1207.375
Parametric Representation of Rank d Tensorial Group Field Theory: Abelian Models with Kinetic Term
We consider the parametric representation of the amplitudes of Abelian models
in the so-called framework of rank Tensorial Group Field Theory. These
models are called Abelian because their fields live on . We concentrate
on the case when these models are endowed with particular kinetic terms
involving a linear power in momenta. New dimensional regularization and
renormalization schemes are introduced for particular models in this class: a
rank 3 tensor model, an infinite tower of matrix models over
, and a matrix model over . For all divergent amplitudes, we
identify a domain of meromorphicity in a strip determined by the real part of
the group dimension . From this point, the ordinary subtraction program is
applied and leads to convergent and analytic renormalized integrals.
Furthermore, we identify and study in depth the Symanzik polynomials provided
by the parametric amplitudes of generic rank Abelian models. We find that
these polynomials do not satisfy the ordinary Tutte's rules
(contraction/deletion). By scrutinizing the "face"-structure of these
polynomials, we find a generalized polynomial which turns out to be stable only
under contraction.Comment: 69 pages, 35 figure
The Great Space Weather Event during February 1872 Recorded in East Asia
The study of historical great geomagnetic storms is crucial for assessing the
possible risks to the technological infrastructure of a modern society, caused
by extreme space-weather events. The normal benchmark has been the great
geomagnetic storm of September 1859, the so-called "Carrington Event". However,
there are numerous records of another great geomagnetic storm in February 1872.
This storm, about 12 years after the Carrington Event, resulted in comparable
magnetic disturbances and auroral displays over large areas of the Earth. We
have revisited this great geomagnetic storm in terms of the auroral and sunspot
records in the historical documents from East Asia. In particular, we have
surveyed the auroral records from East Asia and estimated the equatorward
boundary of the auroral oval to be near 24.3 deg invariant latitude (ILAT), on
the basis that the aurora was seen near the zenith at Shanghai (20 deg magnetic
latitude, MLAT). These results confirm that this geomagnetic storm of February
1872 was as extreme as the Carrington Event, at least in terms of the
equatorward motion of the auroral oval. Indeed, our results support the
interpretation of the simultaneous auroral observations made at Bombay (10 deg
MLAT). The East Asian auroral records have indicated extreme brightness,
suggesting unusual precipitation of high-intensity, low-energy electrons during
this geomagnetic storm. We have compared the duration of the East Asian auroral
displays with magnetic observations in Bombay and found that the auroral
displays occurred in the initial phase, main phase, and early recovery phase of
the magnetic storm.Comment: 28 pages, 5 figures, accepted for publication in the Astrophysical
Journal on 31 May 201
Competing Ground States of the New Class of Halogen-Bridged Metal Complexes
Based on a symmetry argument, we study the ground-state properties of
halogen-bridged binuclear metal chain complexes. We systematically derive
commensurate density-wave solutions from a relevant two-band Peierls-Hubbard
model and numerically draw the the ground-state phase diagram as a function of
electron-electron correlations, electron-phonon interactions, and doping
concentration within the Hartree-Fock approximation. The competition between
two types of charge-density-wave states, which has recently been reported
experimentally, is indeed demonstrated.Comment: 4 pages, 5 figures embedded, to appear in J. Phys. Soc. Jp
Quantum and Thermal Phase Transitions of Halogen-Bridged Binuclear Transition-Metal Complexes
Aiming to settle the controversial observations for halogen-bridged binuclear
transition-metal (MMX) complexes, finite-temperature Hartree-Fock calculations
are performed for a relevant two-band Peierls-Hubbard model. Thermal, as well
as quantum, phase transitions are investigated with particular emphasis on the
competition between electron itinerancy, electron-phonon interaction and
electron-electron correlation. Recently observed distinct thermal behaviors of
two typical MMX compounds Pt_2(CH_3CS_2)_4I and
(NH_4)_4[Pt_2(P_2O_5H_2)_4I]2H_2O are supported and further tuning of their
electronic states is predicted.Comment: 5 pages, 3 figures embedded, to be published in J. Phys. Soc. Jpn.
Vol.70, No.5 (2001
Simulation of the Formation of a Solar Active Region
We present a radiative magnetohydrodynamics simulation of the formation of an
Active Region on the solar surface. The simulation models the rise of a buoyant
magnetic flux bundle from a depth of 7.5 Mm in the convection zone up into the
solar photosphere. The rise of the magnetic plasma in the convection zone is
accompanied by predominantly horizontal expansion. Such an expansion leads to a
scaling relation between the plasma density and the magnetic field strength
such that . The emergence of magnetic flux into the
photosphere appears as a complex magnetic pattern, which results from the
interaction of the rising magnetic field with the turbulent convective flows.
Small-scale magnetic elements at the surface first appear, followed by their
gradual coalescence into larger magnetic concentrations, which eventually
results in the formation of a pair of opposite polarity spots. Although the
mean flow pattern in the vicinity of the developing spots is directed radially
outward, correlations between the magnetic field and velocity field
fluctuations allow the spots to accumulate flux. Such correlations result from
the Lorentz-force driven, counter-streaming motion of opposite-polarity
fragments. The formation of the simulated Active Region is accompanied by
transient light bridges between umbrae and umbral dots. Together with recent
sunspot modeling, this work highlights the common magnetoconvective origin of
umbral dots, light bridges and penumbral filaments.Comment: Accepted for publication in Ap
Photoinduced charge separation in Q1D heterojunction materials: Evidence for electron-hole pair separation in mixed-halide solids
Resonance Raman experiments on doped and photoexcited single crystals of
mixed-halide complexes (=Pt; =Cl,Br) clearly indicate charge
separation: electron polarons preferentially locate on PtBr segments while hole
polarons are trapped within PtCl segments. This polaron selectivity,
potentially very useful for device applications, is demonstrated theoretically
using a discrete, 3/4-filled, two-band, tight-binding, extended Peierls-Hubbard
model. Strong hybridization of the PtCl and PtBr electronic bands is the
driving force for separation.Comment: n LaTeX, figures available by mail from JTG ([email protected]
The Horizontal Component of Photospheric Plasma Flows During the Emergence of Active Regions on the Sun
The dynamics of horizontal plasma flows during the first hours of the
emergence of active region magnetic flux in the solar photosphere have been
analyzed using SOHO/MDI data. Four active regions emerging near the solar limb
have been considered. It has been found that extended regions of Doppler
velocities with different signs are formed in the first hours of the magnetic
flux emergence in the horizontal velocity field. The flows observed are
directly connected with the emerging magnetic flux; they form at the beginning
of the emergence of active regions and are present for a few hours. The Doppler
velocities of flows observed increase gradually and reach their peak values
4-12 hours after the start of the magnetic flux emergence. The peak values of
the mean (inside the +/-500 m/s isolines) and maximum Doppler velocities are
800-970 m/s and 1410-1700 m/s, respectively. The Doppler velocities observed
substantially exceed the separation velocities of the photospheric magnetic
flux outer boundaries. The asymmetry was detected between velocity structures
of leading and following polarities. Doppler velocity structures located in a
region of leading magnetic polarity are more powerful and exist longer than
those in regions of following polarity. The Doppler velocity asymmetry between
the velocity structures of opposite sign reaches its peak values soon after the
emergence begins and then gradually drops within 7-12 hours. The peak values of
asymmetry for the mean and maximal Doppler velocities reach 240-460 m/s and
710-940 m/s, respectively. An interpretation of the observable flow of
photospheric plasma is given.Comment: 20 pages, 10 figures, 3 tables. The results of article were presented
at the ESPM-13 (12-16 September 2011, Rhodes, Greece, Abstract Book p. 102,
P.4.12,
http://astro.academyofathens.gr/espm13/documents/ESPM13_abstract_programme_book.pdf
Holographic Dark Energy Like in Gravity
We investigate the corresponding relation between gravity and
holographic dark energy. We introduce a kind of energy density from
which has role of the same as holographic dark energy.
We obtain the differential equation that specify the evolution of the
introduced energy density parameter based on varying gravitational constant. We
find out a relation for the equation of state parameter to low redshifts which
containing varying correction.Comment: 10 page
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