2,185 research outputs found
Vertex Operators in 4D Quantum Gravity Formulated as CFT
We study vertex operators in 4D conformal field theory derived from quantized
gravity, whose dynamics is governed by the Wess-Zumino action by Riegert and
the Weyl action. Conformal symmetry is equal to diffeomorphism symmetry in the
ultraviolet limit, which mixes positive-metric and negative-metric modes of the
gravitational field and thus these modes cannot be treated separately in
physical operators. In this paper, we construct gravitational vertex operators
such as the Ricci scalar, defined as space-time volume integrals of them are
invariant under conformal transformations. Short distance singularities of
these operator products are computed and it is shown that their coefficients
have physically correct sign. Furthermore, we show that conformal algebra holds
even in the system perturbed by the cosmological constant vertex operator as in
the case of the Liouville theory shown by Curtright and Thorn.Comment: 26 pages, rewrote review part concisely, added explanation
Recursion Relations in Liouville Gravity coupled to Ising Model satisfying Fusion Rules
The recursion relations of 2D quantum gravity coupled to the Ising model
discussed by the author previously are reexamined. We study the case in which
the matter sector satisfies the fusion rules and only the primary operators
inside the Kac table contribute. The theory involves unregularized divergences
in some of correlators. We obtain the recursion relations which form a closed
set among well-defined correlators on sphere, but they do not have a beautiful
structure that the bosonized theory has and also give an inconsistent result
when they include an ill-defined correlator with the divergence. We solve them
and compute the several normalization independent ratios of the well-defined
correlators, which agree with the matrix model results.Comment: Latex, 22 page
Supersymmetric Wilson Loops in IIB Matrix Model
We show that the supersymmetric Wilson loops in IIB matrix model give a
transition operator from reduced supersymmetric Yang-Mills theory to
supersymmetric space-time theory. In comparison with Green-Schwarz superstring
we identify the supersymmetric Wilson loops with the asymptotic states of IIB
superstring. It is pointed out that the supersymmetry transformation law of the
Wilson loops is the inverse of that for the vertex operators of massless modes
in the U(N) open superstring with Dirichlet boundary condition.Comment: 10 pages, Latex, minor typos correcte
Renormalizable 4D Quantum Gravity as A Perturbed Theory from CFT
We study the renormalizable quantum gravity formulated as a perturbed theory
from conformal field theory (CFT) on the basis of conformal gravity in four
dimensions. The conformal mode in the metric field is managed
non-perturbatively without introducing its own coupling constant so that
conformal symmetry becomes exact quantum mechanically as a part of
diffeomorphism invariance. The traceless tensor mode is handled in the
perturbation with a dimensionless coupling constant indicating asymptotic
freedom, which measures a degree of deviation from CFT. There are no massive
ghosts because they are not gauge invariant in this formulation. Higher order
renormalization is carried out using dimensional regularization, in which the
Wess-Zumino integrability condition is applied to reduce indefiniteness
existing in higher-derivative actions. The effective action of quantum gravity
improved by renormalization group is obtained. We then make clear that
conformal anomalies are indispensable quantities to preserve diffeomorphism
invariance. Anomalous scaling dimensions of the cosmological constant and the
Planck mass are calculated. The effective cosmological constant is obtained in
the large number limit of matter fields.Comment: 51 pages, 12 figure
Exponential lower bound on the highest fidelity achievable by quantum error-correcting codes
On a class of memoryless quantum channels which includes the depolarizing
channel, the highest fidelity of quantum error-correcting codes of length n and
rate R is proven to be lower bounded by 1-exp[-nE(R)+o(n)] for some function
E(R). The E(R) is positive below some threshold R', which implies R' is a lower
bound on the quantum capacity.Comment: Ver.4. In vers.1--3, I claimed Theorem 1 for general quantum
channels. Now I claim this only for a slight generalization of depolarizing
channel in this paper because Lemma 2 in vers.1--3 was wrong; the original
general statement is proved in quant-ph/0112103. Ver.5. Text sectionalized.
Appeared in PRA. The PRA article is typographically slightly crude: The LaTeX
symbol star, used as superscripts, was capriciously replaced by the asterisk
in several places after my proof readin
Tema Con Variazioni: Quantum Channel Capacity
Channel capacity describes the size of the nearly ideal channels, which can
be obtained from many uses of a given channel, using an optimal error
correcting code. In this paper we collect and compare minor and major
variations in the mathematically precise statements of this idea which have
been put forward in the literature. We show that all the variations considered
lead to equivalent capacity definitions. In particular, it makes no difference
whether one requires mean or maximal errors to go to zero, and it makes no
difference whether errors are required to vanish for any sequence of block
sizes compatible with the rate, or only for one infinite sequence.Comment: 32 pages, uses iopart.cl
Evidence of different climatic adaptation strategies in humans and non-human primates
Abstract: To understand human evolution it is critical to clarify which adaptations enabled our colonisation of novel ecological niches. For any species climate is a fundamental source of environmental stress during range expansion. Mammalian climatic adaptations include changes in size and shape reflected in skeletal dimensions and humans fit general primate ecogeographic patterns. It remains unclear however, whether there are also comparable amounts of adaptation in humans, which has implications for understanding the relative importance of biological/behavioural mechanisms in human evolution. We compare cranial variation between prehistoric human populations from throughout Japan and ecologically comparable groups of macaques. We compare amounts of intraspecific variation and covariation between cranial shape and ecological variables. Given equal rates and sufficient time for adaptation for both groups, human conservation of non-human primate adaptation should result in comparable variation and patterns of covariation in both species. In fact, we find similar amounts of intraspecific variation in both species, but no covariation between shape and climate in humans, contrasting with strong covariation in macaques. The lack of covariation in humans may suggest a disconnect in climatic adaptation strategies from other primates. We suggest this is due to the importance of human behavioural adaptations, which act as a buffer from climatic stress and were likely key to our evolutionary success
On Electron Transport in ZrB12, ZrB2 and MgB2
We report on measurements of the temperature dependence of resistivity,
, for single crystal samples of ZrB, ZrB and
polycrystalline samples of MgB. It is shown that cluster compound
ZrB behaves like a simple metal in the normal state, with a typical
Bloch -- Gr\"uneisen dependence. However, the resistive Debye
temperature, , is three times smaller than obtained from
specific heat data. We observe the term in of these borides,
which could be interpreted as an indication of strong electron-electron
interaction. Although the dependence of ZrB reveals a sharp
superconductive transition at , no superconductivity was observed
for single crystal samples of ZrB down to .Comment: 5 pages, 4 figure
Nontrivial behavior of the Fermi arc in the staggered-flux ordered phase
The doping and temperature dependences of the Fermi arc in the
staggered-flux, or the d-density wave, ordered phase of the t-J model are
analyzed by the U(1) slave boson theory. Nontrivial behavior is revealed by the
self-consistent calculation. At low doped and finite-temperature region, both
the length of the Fermi arc and the width of the Fermi pocket are proportional
to and the area of the Fermi pocket is proportional to .
This behavior is completely different from that at the zero temperature, where
the area of the Fermi pocket becomes . This behavior should be
observed by detailed experiments of angle-resolved photoemission spectroscopy
in the pseudogap phase of high-T_c cuprates if the pseudogap phase is the
staggered-flux ordered phase.Comment: 4 pages, 4 figure
Pressure Effects in Manganites with Layered Perovskite Structure
Pressure effects on the charge and spin dynamics in the bilayer manganite
compounds are studied theoretically by taking into
account the orbital degrees of freedom. The orbital degrees are active in the
layered crystal structure, and applied hydrostatic pressure stabilizes the
orbital in comparison with . The change of the
orbital states weakens the interlayer charge and spin couplings, and suppresses
the three dimensional ferromagnetic transition. Numerical results, based on an
effective Hamiltonian which includes the energy level difference of the
orbitals, show that the applied pressure controls the dimensionality of the
spin and charge dynamics through changes of the orbital states.Comment: 5 pages, 2 figure
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