2,884 research outputs found
The String Tension in Two Dimensional Gauge Theories
We review and elaborate on properties of the string tension in
two-dimensional gauge theories. The first model we consider is massive QED in
the limit. We evaluate the leading string tension both in the
fermionic and bosonized descriptions. We discuss the next to leading
corrections in . The next-to-leading terms in the long distance behavior
of the quark-antiquark potential, are evaluated in a certain region of external
versus dynamical charges. The finite temperature behavior is also determined.
In we review the results for the string tension of quarks in cases with
dynamical quarks in the fundamental, adjoint, symmetric and antisymmetric
representations. The screening nature of is re-derived.Comment: 25 pages, Latex. v2: several changes, mainly in section
Resonance ionization spectroscopy of thorium isotopes - towards a laser spectroscopic identification of the low-lying 7.6 eV isomer of Th-229
In-source resonance ionization spectroscopy was used to identify an efficient
and selective three step excitation/ionization scheme of thorium, suitable for
titanium:sapphire (Ti:sa) lasers. The measurements were carried out in
preparation of laser spectroscopic investigations for an identification of the
low-lying Th-229m isomer predicted at 7.6 +- 0.5 eV above the nuclear ground
state. Using a sample of Th-232, a multitude of optical transitions leading to
over 20 previously unknown intermediate states of even parity as well as
numerous high-lying odd parity auto-ionizing states were identified. Level
energies were determined with an accuracy of 0.06 cm-1 for intermediate and
0.15 cm-1 for auto-ionizing states. Using different excitation pathways an
assignment of total angular momenta for several energy levels was possible. One
particularly efficient ionization scheme of thorium, exhibiting saturation in
all three optical transitions, was studied in detail. For all three levels in
this scheme, the isotope shifts of the isotopes Th-228, Th-229, and Th-230
relative to Th-232 were measured. An overall efficiency including ionization,
transport and detection of 0.6 was determined, which was predominantly limited
by the transmission of the mass spectrometer ion optics
Isomeric states close to doubly magic Sn studied with JYFLTRAP
The double Penning trap mass spectrometer JYFLTRAP has been employed to
measure masses and excitation energies for isomers in Cd,
Cd, Cd and Te, for isomers in In and
In, and for isomers in Sn and Sb. These first
direct mass measurements of the Cd and In isomers reveal deviations to the
excitation energies based on results from beta-decay experiments and yield new
information on neutron- and proton-hole states close to Sn. A new
excitation energy of 144(4) keV has been determined for Cd. A good
agreement with the precisely known excitation energies of Cd,
Sn, and Sb has been found.Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Exotic Non-Supersymmetric Gauge Dynamics from Supersymmetric QCD
We extend Seiberg's qualitative picture of the behavior of supersymmetric QCD
to nonsupersymmetric models by adding soft supersymmetry breaking terms. In
this way, we recover the standard vacuum of QCD with flavors and
colors when . However, for , we find new exotic
states---new vacua with spontaneously broken baryon number for , and
a vacuum state with unbroken chiral symmetry for . These exotic
vacua contain massless composite fermions and, in some cases, dynamically
generated gauge bosons. In particular Seiberg's electric-magnetic duality seems
to persist also in the presence of (small) soft supersymmetry breaking. We
argue that certain, specially tailored, lattice simulations may be able to
detect the novel phenomena. Most of the exotic behavior does not survive the
decoupling limit of large SUSY breaking parameters.Comment: 36 pages, latex + 2 figures (uuencoded ps
A Soluble String Theory of Hadrons
We consider Penrose limits of the Klebanov-Strassler and Maldacena-Nunez
holographic duals to N =1 supersymmetric Yang-Mills. By focusing in on the IR
region we obtain exactly solvable string theory models. These represent the
nonrelativistic motion and low-lying excitations of heavy hadrons with mass
proportional to a large global charge. We argue that these hadrons, both
physically and mathematically, take the form of heavy nonrelativistic strings;
we term them "annulons." A simple toy model of a string boosted along a compact
circle allows us considerable insight into their properties. We also calculate
the Wilson loop carrying large global charge and show the effect of confinement
is quadratic, not linear, in the string tension.Comment: 40 pages, 1 figure; v2: typos correcte
Supergravity and The Large N Limit of Theories With Sixteen Supercharges
We consider field theories with sixteen supersymmetries, which includes U(N)
Yang-Mills theories in various dimensions, and argue that their large N limit
is related to certain supergravity solutions. We study this by considering a
system of D-branes in string theory and then taking a limit where the brane
worldvolume theory decouples from gravity. At the same time we study the
corresponding D-brane supergravity solution and argue that we can trust it in
certain regions where the curvature (and the effective string coupling, where
appropriate) are small. The supergravity solutions typically have several
weakly coupled regions and interpolate between different limits of
string-M-theory.Comment: 24 pages, latex. v2: reference added, v3: typos correcte
Integrability of Type II Superstrings on Ramond-Ramond Backgrounds in Various Dimensions
We consider type II superstrings on AdS backgrounds with Ramond-Ramond flux
in various dimensions. We realize the backgrounds as supercosets and analyze
explicitly two classes of models: non-critical superstrings on AdS_{2d} and
critical superstrings on AdS_p\times S^p\times CY. We work both in the
Green--Schwarz and in the pure spinor formalisms. We construct a one-parameter
family of flat currents (a Lax connection) leading to an infinite number of
conserved non-local charges, which imply the classical integrability of both
sigma-models. In the pure spinor formulation, we use the BRST symmetry to prove
the quantum integrability of the sigma-model. We discuss how classical
\kappa-symmetry implies one-loop conformal invariance. We consider the addition
of space-filling D-branes to the pure spinor formalism.Comment: LaTeX2e, 56 pages, 1 figure, JHEP style; v2: references added, typos
fixed in some equations; v3: typos fixed to match the published versio
Non-holomorphic terms in N=2 SUSY Wilsonian actions and RG equation
In this paper we first investigate the Ansatz of one of the present authors
for K(\Psi,\bar\Psi), the adimensional modular invariant non-holomorphic
correction to the Wilsonian effective Lagrangian of an N=2 globally
supersymmetric gauge theory. The renormalisation group beta-function of the
theory crucially allows us to express K(\Psi,\bar\Psi) in a form that easily
generalises to the case in which the theory is coupled to N_F hypermultiplets
in the fundamental representation of the gauge group. This function satisfies
an equation which should be viewed as a fully non-perturbative ``non-chiral
superconformal Ward identity". We also determine its renormalisation group
equation. Furthermore, as a first step towards checking the validity of this
Ansatz, we compute the contribution to K(\Psi,\bar\Psi) from instantons of
winding number k=1 and k=2. As a by-product of our analysis we check a
non-renormalisation theorem for N_F=4.Comment: 39 pages, LaTex file, no figure
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