10,247 research outputs found
Temperature Power Law of Equilibrium Heavy Particle Density
A standard calculation of the energy density of heavy stable particles that
may pair-annihilate into light particles making up thermal medium is performed
to second order of coupling, using the technique of thermal field theory. At
very low temperatures a power law of temperature is derived for the energy
density of the heavy particle. This is in sharp contrast to the exponentially
suppressed contribution estimated from the ideal gas distribution function. The
result supports a previous dynamical calculation based on the Hartree
approximation, and implies that the relic abundance of dark matter particles is
enhanced compared to that based on the Boltzmann equation.Comment: 12 pages, LATEX file with 6 PS figure
Noise Tolerance of the BB84 Protocol with Random Privacy Amplification
We prove that BB84 protocol with random privacy amplification is secure with
a higher key rate than Mayers' estimate with the same error rate. Consequently,
the tolerable error rate of this protocol is increased from 7.5 % to 11 %. We
also extend this method to the case of estimating error rates separately in
each basis, which enables us to securely share a longer key.Comment: 26 pages, 1 figure, version 2 fills a logical gap in the proof.
Version 3 includes an upper bound on the mutual information with finete code
length by using the decoding error probability of the code. Version 4 adds a
paragraph clarifying that no previous paper has proved that the BB84 with
random privacy amplification can tolerate the 11% error rat
Robustly Unstable Eigenmodes of the Magnetoshearing Instability in Accretion Disk
The stability of nonaxisymmetric perturbations in differentially rotating
astrophysical accretion disks is analyzed by fully incorporating the properties
of shear flows. We verify the presence of discrete unstable eigenmodes with
complex and pure imaginary eigenvalues, without any artificial disk edge
boundaries, unlike Ogilvie & Pringle(1996)'s claim. By developing the
mathematical theory of a non-self-adjoint system, we investigate the nonlocal
behavior of eigenmodes in the vicinity of Alfven singularities at
omega_D=omega_A, where omega_D is the Doppler-shifted wave frequency and
omega_A=k_// v_A is the Alfven frequency. The structure of the spectrum of
discrete eigenmodes is discussed and the magnetic field and wavenumber
dependence of the growth rate are obtained. Exponentially growing modes are
present even in a region where the local dispersion relation theory claims to
have stable eigenvalues. The velocity field created by an eigenmode is
obtained, which explains the anomalous angular momentum transport in the
nonlinear stage of this stability.Comment: 11pages, 11figures, to be published in ApJ. For associated eps files,
see http://dino.ph.utexas.edu/~knoguchi
Randomly Diluted e_g Orbital-Ordered Systems
Dilution effects on the long-range ordered state of the doubly degenerate
orbital are investigated. Quenched impurities without the orbital degree
of freedom are introduced in the orbital model where the long-range order is
realized by the order-from-disorder mechanism. It is shown by the Monte-Carlo
simulation and the cluster-expansion method that a decrease in the orbital
ordering temperature by dilution is remarkable in comparison with that in the
randomly diluted spin models. Tiltings of orbitals around impurity cause this
unique dilution effects on the orbital systems. The present theory provides a
new view point for the recent experiments in KCuZnF.Comment: 4 pages, 4 figure
On Witten multiple zeta-functions associated with semisimple Lie algebras IV
In our previous work, we established the theory of multi-variable Witten
zeta-functions, which are called the zeta-functions of root systems. We have
already considered the cases of types , , , and . In
this paper, we consider the case of -type. We define certain analogues of
Bernoulli polynomials of -type and study the generating functions of them
to determine the coefficients of Witten's volume formulas of -type. Next
we consider the meromorphic continuation of the zeta-function of -type and
determine its possible singularities. Finally, by using our previous method, we
give explicit functional relations for them which include Witten's volume
formulas.Comment: 22 pag
Generalized -conformal change and special Finsler spaces
In this paper, we investigate the change of Finslr metrics which we refer to as a
generalized -conformal change. Under this change, we study some special
Finsler spaces, namely, quasi C-reducible, semi C-reducible, C-reducible,
-like, -like and -like Finsler spaces. We also obtain the
transformation of the T-tensor under this change and study some interesting
special cases. We then impose a certain condition on the generalized
-conformal change, which we call the b-condition, and investigate the
geometric consequences of such condition. Finally, we give the conditions under
which a generalized -conformal change is projective and generalize some
known results in the literature.Comment: References added, some modifications are performed, LateX file, 24
page
Single Impurity Effects in Multiband Superconductors with Different Sign Order Parameters
A single impurity problem is investigated for multiband s-wave
superconductors with different sign order parameters (+-s-wave superconductors)
suggested in Fe-pnictide superconductors. Not only intraband but also interband
scattering is considered at the impurity. The latter gives rise to
impurity-induced local boundstates close to the impurity. We present an exact
form of the energy of the local boundstates as a function of strength of the
two types of impurity scattering. The essential role of the impurity is
unchanged in finite number of impurities. The main conclusions for a single
impurity problem help us understand effects of dense impurities in the +-s-wave
superconductors. Local density of states around the single impurity is also
investigated. We suggest impurity site nuclear magnetic resonance as a suitable
experiment to probe the local boundstates that is peculiar to the +-s-wave
state. We find that the +-s-wave model is mapped to a chiral dx2-y2+-idxy-wave,
reflecting the unconventional nature of the sign reversing order parameter. For
a quantum magnetic impurity, interband scattering destabilizes the Kondo
singlet.Comment: 23 pages, 7 figures, to be published in J. Phys. Soc. Jpn. (2009) No.
A Note on the Slim Accretion Disk Model
We show that when the gravitational force is correctly calculated in dealing
with the vertical hydrostatic equilibrium of black hole accretion disks, the
relationship that is valid for geometrically thin disks, i.e., constant, where is the sound speed, is the Keplerian
angular velocity, and is the half-thickness of the disk, does not hold for
slim disks. More importantly, by adopting the correct vertical gravitational
force in studies of thermal equilibrium solutions, we find that there exists a
maximally possible accretion rate for each radius in the outer region of
optically thick accretion flows, so that only the inner region of these flows
can possibly take the form of slim disks, and strong outflows from the outer
region are required to reduce the accretion rate in order for slim disks to be
realized.Comment: 14 pages, 5 figures, accepted by Ap
- âŠ