3,148 research outputs found
On the effective potential in higher-derivative superfield theories
We study the one-loop quantum corrections for higher-derivative superfield
theories, generalizing the approach for calculating the superfield effective
potential. In particular, we calculate the effective potential for two versions
of higher-derivative chiral superfield models. We point out that the
equivalence of the higher-derivative theory for the chiral superfield and the
one without higher derivatives but with an extended number of chiral
superfields occurs only when the mass term is contained in the general
Lagrangian. The presence of divergences can be taken as an indication of this
equivalence.Comment: 14 page
Exact propagators in harmonic superspace
Within the background field formulation in harmonic superspace for quantum N
= 2 super Yang-Mills theories, the propagators of the matter, gauge and ghost
superfields possess a complicated dependence on the SU(2) harmonic variables
via the background vector multiplet. This dependence is shown to simplify
drastically in the case of an on-shell vector multiplet. For a covariantly
constant background vector multiplet, we exactly compute all the propagators.
In conjunction with the covariant multi-loop scheme developed in
hep-th/0302205, these results provide an efficient (manifestly N = 2
supersymmetric) technical setup for computing multi-loop quantum corrections to
effective actions in N = 2 supersymmetric gauge theories, including the N = 4
super Yang-Mills theory.Comment: Latex, 12 pages; V2: a reference added; V3: typos in eq. (3)
corrected, the version to appear in PLB; V4: typos in eq. (47) correcte
Partial Supersymmetry Breaking and N=2 U(N_c) Gauge Model with Hypermultiplets in Harmonic Superspace
We provide a manifestly N=2 supersymmetric formulation of the N=2 U(N_c)
gauge model constructed in terms of N=1 superfields in hep-th/0409060. The
model is composed of N=2 vector multiplets in harmonic superspace and can be
viewed as the N=2 U(N_c) Yang-Mills effective action equipped with the electric
and magnetic Fayet-Iliopoulos terms. We generalize this gauge model to an N=2
U(N_c) QCD model by introducing N=2 hypermultiplets in harmonic superspace
which include both the fundamental representation of U(N_c) and the adjoint
representation of U(N_c). The effect of the magnetic Fayet-Iliopoulos term is
to shift the auxiliary field by an imaginary constant. Examining vacua of the
model, we show that N=2 supersymmetry is spontaneously broken down to N=1.Comment: 26 pages; typos fixed; version to appear in Nucl.Phys.B; eqn.(2.4)
and typos correcte
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
On the D = 4, N = 2 Non-Renormalization Theorem
Using the harmonic superspace background field formulation for general D=4,
N=2 super Yang-Mills theories, with matter hypermultiplets in arbitrary
representations of the gauge group, we present the first rigorous proof of the
N=2 non-renormalization theorem; specifically, the absence of ultraviolet
divergences beyond the one-loop level. Another simple consequence of the
background field formulation is the absence of the leading non-holomorphic
correction to the low-energy effective action at two loops.Comment: 16 pages, LATEX, uses FEYMAN macros, minor change
Covariant Harmonic Supergraphity for N = 2 Super Yang--Mills Theories
We review the background field method for general N = 2 super Yang-Mills
theories formulated in the N = 2 harmonic superspace. The covariant harmonic
supergraph technique is then applied to rigorously prove the N=2
non-renormalization theorem as well as to compute the holomorphic low-energy
action for the N = 2 SU(2) pure super Yang-Mills theory and the leading
non-holomorphic low-energy correction for N = 4 SU(2) super Yang-Mills theory.Comment: 17 pages, LAMUPHYS LaTeX, no figures; based on talks given by I.
Buchbinder and S. Kuzenko at the International Seminar ``Supersymmetries and
Quantum Symmetries'', July 1997, Dubna; to be published in the proceeding
Five-dimensional supersymmetric Chern-Simons action as a hypermultiplet quantum correction
Building on the covariant supergraph techniques in 4D N = 2 harmonic
superspace, we develop a manifestly 5D N = 1 supersymmetric and gauge covariant
formalism to compute the one-loop effective action for a hypermultiplet coupled
to a background vector multiplet. As a simple application, we demonstrate the
generation of a supersymmetric Chern-Simons action at the quantum level, both
in the Coulomb and the non-Abelian phases. These superfield results are in
agreement with the earlier component considerations of Seiberg et al. Our
analysis suggests that similar calculations in terms of hybrid 4D superfields
or within the 5D projective superspace approach may allow one to extract
suitable formulations for the non-Abelian 5D supersymmetric Chern-Simons
theory.Comment: 12 page
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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