14,605 research outputs found
Massive Hyper-Kahler Sigma Models and BPS Domain Walls
With the non-Abelian Hyper-Kahler quotient by U(M) and SU(M) gauge groups, we
give the massive Hyper-Kahler sigma models that are not toric in the N=1
superfield formalism. The U(M) quotient gives N!/[M! (N-M)!] (N is a number of
flavors) discrete vacua that may allow various types of domain walls, whereas
the SU(M) quotient gives no discrete vacua. We derive BPS domain wall solution
in the case of N=2 and M=1 in the U(M) quotient model.Comment: 16 pages, 1 figure, contribution to the Proceedings of the
International Conference on "Symmetry Methods in Physics (SYM-PHYS10)" held
at Yerevan, Armenia, 13-19 Aug. 200
Distinguished self-adjoint extensions of Dirac operators via Hardy-Dirac inequalities
We prove some Hardy-Dirac inequalities with two different weights including
measure valued and Coulombic ones. Those inequalities are used to construct
distinguished self-adjoint extensions of Dirac operators for a class of
diagonal potentials related to the weights in the above mentioned inequalities.Comment: 16 page
Field evolution of the magnetic structures in ErTiO through the critical point
We have measured neutron diffraction patterns in a single crystal sample of
the pyrochlore compound ErTiO in the antiferromagnetic phase
(T=0.3\,K), as a function of the magnetic field, up to 6\,T, applied along the
[110] direction. We determine all the characteristics of the magnetic structure
throughout the quantum critical point at =2\,T. As a main result, all Er
moments align along the field at and their values reach a minimum. Using
a four-sublattice self-consistent calculation, we show that the evolution of
the magnetic structure and the value of the critical field are rather well
reproduced using the same anisotropic exchange tensor as that accounting for
the local paramagnetic susceptibility. In contrast, an isotropic exchange
tensor does not match the moment variations through the critical point. The
model also accounts semi-quantitatively for other experimental data previously
measured, such as the field dependence of the heat capacity, energy of the
dispersionless inelastic modes and transition temperature.Comment: 7 pages; 8 figure
Matrix representation of the time operator
In quantum mechanics the time operator satisfies the commutation
relation , and thus it may be thought of as being canonically
conjugate to the Hamiltonian . The time operator associated with a given
Hamiltonian is not unique because one can replace by , where satisfies the homogeneous condition
. To study this nonuniqueness the matrix elements of
for the harmonic-oscillator Hamiltonian are calculated in the
eigenstate basis. This calculation requires the summation of divergent series,
and the summation is accomplished by using zeta-summation techniques. It is
shown that by including appropriate homogeneous contributions, the matrix
elements of simplify dramatically. However, it is still not clear
whether there is an optimally simple representation of the time operator.Comment: 13 pages, 3 figure
On the Spectral Analysis of Quantum Electrodynamics with Spatial Cutoffs. I
In this paper, we consider the spectrum of a model in quantum electrodynamics
with a spatial cutoff. It is proven that (1) the Hamiltonian is self-adjoint;
(2) under the infrared regularity condition, the Hamiltonian has a unique
ground state for sufficiently small values of coupling constants. The spectral
scattering theory is studied as well and it is shown that asymptotic fields
exist and the spectral gap is closed
Amplitude dependence of image quality in atomically-resolved bimodal atomic microscopy
In bimodal FM-AFM, two flexural modes are excited simultaneously. The total
vertical oscillation deflection range of the tip is the sum of the peak-to-peak
amplitudes of both flexural modes (sum amplitude). We show atomically resolved
images of KBr(100) in ambient conditions in bimodal AFM that display a strong
correlation between image quality and sum amplitude. When the sum amplitude
becomes larger than about 200 pm, the signal-to-noise ratio (SNR) is
drastically decreased. We propose this is caused by the temporary presence of
one or more water layers in the tip-sample gap. These water layers screen the
short range interaction and must be displaced with each oscillation cycle.
Further decreasing the sum amplitude, however, causes a decrease in SNR.
Therefore, the highest SNR in ambient conditions is achieved when the sum
amplitude is slightly less than the thickness of the primary hydration layer.Comment: 3000 words, 3 Figures, 3 supplimentary figure
Femtosecond laser nanostructuring of transparent materials: from bulk to fiber lasers
Progress in high power ultra-short pulse lasers has opened new frontiers in the physics of light-matter interactions and laser material processing. Recently there has been considerable interest in the application of femtosecond lasers to writing inside transparent materials and in particular to fabrication of three-dimensional microstructures
Channel Capacity Enhancement by Pattern Controlled Handset Antenna
This paper presents a radiation pattern controlled antenna for handset terminals to reduce the correlation coefficient between antennas and enhance the channel capacity in MIMO applications. A pair of small inverted-F shaped antennas combined by a phase shifter provides a single port with controlled pattern. To enhance the channel capacity, the phase difference for the IFA array is optimized using the evaluation parameter of reception level, correlation coefficient and mean effective gain of the proposed array geometry. The channel capacity enhancement is verified by assuming Croneker scattering under Nakagami-Rice propagation model
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