7,830 research outputs found
On Mirror Symmetry for Calabi-Yau Fourfolds with Three-Form Cohomology
We study the action of mirror symmetry on two-dimensional N=(2,2) effective
theories obtained by compactifying Type IIA string theory on Calabi-Yau
fourfolds. Our focus is on fourfold geometries with non-trivial three-form
cohomology. The couplings of the massless zero-modes arising by expanding in
these forms depend both on the complex structure deformations and the Kahler
structure deformations of the Calabi-Yau fourfold. We argue that two
holomorphic functions of the deformation moduli capture this information. These
are exchanged under mirror symmetry, which allows us to derive them at the
large complex structure and large volume point. We discuss the application of
the resulting explicit expression to F-theory compactifications and their weak
string coupling limit. In the latter orientifold settings we demonstrate
compatibility with mirror symmetry of Calabi-Yau threefolds at large complex
structure. As a byproduct we find an interesting relation of no-scale like
conditions on Kahler potentials to the existence of chiral and twisted-chiral
descriptions in two dimensions.Comment: 36 page
Relativistic Hartree approach including both positive- and negative-energy bound states
We develop a relativistic model to describe the bound states of positive
energy and negative energy in finite nuclei at the same time. Instead of
searching for the negative-energy solution of the nucleon's Dirac equation, we
solve the Dirac equations for the nucleon and the anti-nucleon simultaneously.
The single-particle energies of negative-energy nucleons are obtained through
changing the sign of the single-particle energies of positive-energy
anti-nucleons. The contributions of the Dirac sea to the source terms of the
meson fields are evaluated by means of the derivative expansion up to the
leading derivative order for the one-meson loop and one-nucleon loop. After
refitting the parameters of the model to the properties of spherical nuclei,
the results of positive-energy sector are similar to that calculated within the
commonly used relativistic mean field theory under the no-sea approximation.
However, the bound levels of negative-energy nucleons vary drastically when the
vacuum contributions are taken into account. It implies that the
negative-energy spectra deserve a sensitive probe to the effective interactions
in addition to the positive-energy spectra.Comment: 38 pages, Latex, 8 figures included; Int. J. Mod. Phys. E, in pres
Calculation of electron-positron production in supercritical uranium-uranium collisions near the Coulomb barrier
The time-dependent Dirac equation was solved for zero-impact-parameter bare
U-U collisions in the monopole approximation using a mapped Fourier grid matrix
representation. A total of 2048 states including bound, as well as positive-
and negative-energy states for an N=1024 spatial grid were propagated to
generate occupation amplitudes as a function of internuclear separation. From
these amplitudes spectra were calculated for total inclusive positron and
electron production, and also the correlated spectra for () pair
production. These were analyzed as a function of nuclear sticking time in order
to establish signatures of spontaneous pair creation, i.e., QED vacuum decay.
Subcritical Fr-Fr and highly supercritical Db-Db collisions both at the Coulomb
barrier were also studied and contrasted with the U-U results.Comment: 20 pages, 4 page
The phase-space structure of the Klein-Gordon field
The formalism based on the equal-time Wigner function of the two-point
correlation function for a quantized Klein--Gordon field is presented. The
notion of the gauge-invariant Wigner transform is introduced and equations for
the corresponding phase-space calculus are formulated. The equations of motion
governing the Wigner function of the Klein--Gordon field are derived. It is
shown that they lead to a relativistic transport equation with electric and
magnetic forces and quantum corrections. The governing equations are much
simpler than in the fermionic case which has been treated earlier. In addition
the newly developed formalism is applied towards the description of spontaneous
symmetry breakdown.Comment: 27 pages, LaTeX, UFTP 317/199
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