169 research outputs found
Standard Model bundles of the heterotic string
We show how to construct supersymmetric three-generation models with gauge
group and matter content of the Standard Model in the framework of
non-simply-connected elliptically fibered Calabi-Yau manifolds Z. The elliptic
fibration on a cover Calabi-Yau, where the model has 6 generations of SU(5) and
the bundle is given via the spectral cover description, has a second section
leading to the needed free involution. The relevant involution on the defining
spectral data of the bundle is identified for a general Calabi-Yau of this type
and invariant bundles are generally constructible.Comment: 23 pp; minor remarks adde
The Background Field Method for N = 2 Super Yang-Mills Theories in Harmonic Superspace
The background field method for N=2 super Yang-Mills theories in harmonic
superspace is developed. The ghost structure of the theory is investigated. It
is shown that the ghosts include two fermionic real omega-hypermultiplets
(Faddeev-Popov ghosts) and one bosonic real omega-hypermultiplet
(Nielsen-Kallosh ghost), all in the adjoint representation of the gauge group.
The one-loop effective action is analysed in detail and it is found that its
structure is determined only by the ghost corrections in the pure super
Yang-Mills theory. As applied to the case of N=4 super Yang-Mills theory,
realized in terms of N=2 superfields, the latter result leads to the remarkable
conclusion that the one-loop effective action of the theory does not contain
quantum corrections depending on the N=2 gauge superfield only. We show that
the leading low-energy contribution to the one-loop effective action in the N=2
SU(2) super Yang-Mills theory coincides with Seiberg's perturbative holomorphic
effective action.Comment: 17 pages, Late
Ionization corrections in a multi-phase interstellar medium: Lessons from a z~2 sub-DLA
We present a high resolution (FWHM=2.7 km/s), high S/N echelle spectrum for
the z = 2.26 QSO J2123-0050 and determine elemental abundances for the z = 2.06
sub-DLA in its line of sight. This high redshift sub-DLA has a complex
kinematic structure and harbours detections of neutral (SI, CI), singly (e.g.
CII, SII) and multiply ionized (e.g. CIV, SiIV) species as well as molecular H
and HD. The plethora of detected transitions in various ionization stages is
indicative of a complex multi-phase structure present in this high redshift
galaxy. We demonstrate that the ionization corrections in this sub-DLA are
significant (up to ~0.7 dex). For example, if no ionization correction is
applied, a super-solar metallicity is derived ([S/H] = +0.36), whereas a single
phase ionization correction reduces this to [S/H] = -0.19. The theoretical
impact of a multi-phase medium is investigated through Cloudy modelling and it
is found that the abundances of Si, S and Fe are always over-estimated (by up
to 0.15 dex in our experiments) if a single-phase is assumed. Therefore,
although Cloudy models improve estimates of metal column densities, the
simplification of a single phase medium leaves a systematic error in the
result, so that even ionization-corrected abundances may still be too high.
Without ionization corrections the properties of this sub-DLA appear to require
extreme scenarios of nucleosynthetic origins. After ionization corrections are
applied the ISM of this galaxy appears to be similar to some of the sightlines
through the Milky Way.Comment: Accepted for publication in MNRA
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