123,035 research outputs found
Algebraic spin liquid as the mother of many competing orders
We study the properties of a class of two-dimensional interacting critical
states -- dubbed algebraic spin liquids -- that can arise in two-dimensional
quantum magnets. A particular example that we focus on is the staggered flux
spin liquid, which plays a key role in some theories of underdoped cuprate
superconductors. We show that the low-energy theory of such states has much
higher symmetry than the underlying microscopic spin system. This symmetry has
remarkable consequences, leading in particular to the unification of a number
of seemingly unrelated competing orders. The correlations of these orders --
including, in the staggered flux state, the Neel vector and the order parameter
for the columnar and box valence-bond solid states -- all exhibit the SAME slow
power-law decay. Implications for experiments in the pseudogap regime of the
cuprates and for numerical calculations on model systems are discussed.Comment: Minor changes; final published version. 17 pages, 3 figure
Precision Gauge Unification from Extra Yukawa Couplings
We investigate the impact of extra vector-like GUT multiplets on the
predicted value of the strong coupling. We find in particular that Yukawa
couplings between such extra multiplets and the MSSM Higgs doublets can resolve
the familiar two-loop discrepancy between the SUSY GUT prediction and the
measured value of alpha_3. Our analysis highlights the advantages of the
holomorphic scheme, where the perturbative running of gauge couplings is
saturated at one loop and further corrections are conveniently described in
terms of wavefunction renormalization factors. If the gauge couplings as well
as the extra Yukawas are of O(1) at the unification scale, the relevant
two-loop correction can be obtained analytically. However, the effect persists
also in the weakly-coupled domain, where possible non-perturbative corrections
at the GUT scale are under better control.Comment: 26 pages, LaTeX. v6: Important early reference adde
Higher Loop Effects on Unification via Kaluza-Klein Thresholds
We discuss higher loop corrections to gauge coupling renormalization in the
context of gauge coupling unification via Kaluza-Klein thresholds. We show that
in the case N=1 supersymmetric compactifications the one-loop threshold
contributions are dominant, while the higher loop correction are subleading.
This is due to the fact that at heavy Kaluza-Klein levels the spectrum as well
as the interactions are N=2 supersymmetric. In particular, we give two
different arguments leading to this result - one is field theoretic, while the
second one utilizes the power of string perturbation techniques. To illustrate
our discussions we perform explicit two-loop computations of various
corrections to gauge couplings within this framework. We also remark on
phenomenological applications of our discussions in the context of TeV-scale
brane world.Comment: 27 pages, revtex; minor misprints corrected, some comments modified
(to appear in Nucl. Phys. B
Renormalizable Adjoint SU(5)
We investigate the possibility to find the simplest renormalizable grand
unified theory based on the SU(5) gauge symmetry. We find that it is possible
to generate all fermion masses with only two Higgs bosons, 5_H and 45_H. In
this context the neutrino masses are generated through the type III and type I
seesaw mechanisms. The predictions coming from the unification of gauge
couplings and the stability of the proton are discussed in detail. In this
theory the leptogenesis mechanism can be realized through the out of
equilibrium decays of the fermions in the adjoint representation.Comment: 6 pages, minor corrections, to appear in Physics Letters
Higher-order Linear Logic Programming of Categorial Deduction
We show how categorial deduction can be implemented in higher-order (linear)
logic programming, thereby realising parsing as deduction for the associative
and non-associative Lambek calculi. This provides a method of solution to the
parsing problem of Lambek categorial grammar applicable to a variety of its
extensions.Comment: 8 pages LaTeX, uses eaclap.sty, to appear EACL9
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