115154910
New self-dual solutions of SU(2) Yang-Mills theory in Euclidean Schwarzschild space
We present a systematic study of spherically symmetric self-dual solutions of SU(2) Yang-Mills theory on Euclidean Schwarzschild space. All the previously known solutions are recovered and a new one-parameter family of instantons is obtained. The newly found solutions have continuous actions and interpolate between the classic Charap and Duff instantons. We examine the physical properties of this family and show that it consists of dyons of unit (magnetic and electric) charge.
119273247
A solution of 2D QCD at Finite $N$ using a conformal basis
We study 2D QCD with a fundamental fermion at small-$N$ using the recently proposed conformal basis approach. We find that effective conformal dominance still holds, namely that the spectrum converges efficiently, with high scaling-dimension operators decoupling exponentially quickly from the stable single-particle states. Consequently, for these stable bound states, accurate, analytic expressions for wavefunctions and parton distribution functions can be given, even for $N=3$.
118488366
Solving 2D QCD with an adjoint fermion analytically
A bstractWe present an analytic approach to solving 1 + 1 dimensional QCD with an adjoint Majorana fermion. In the UV this theory is described by a trivial CFT containing free fermions. The quasi-primary operators of this CFT lead to a discrete basis of states which is useful for diagonalizing the Hamiltonian of the full strongly interacting theory. Working at large-N, we find that the decoupling of high scaling-dimension quasi-primary operators from the low-energy spectrum occurs exponentially fast in their scaling-dimension. This suggests a scheme, whereby, truncating the basis to operators of dimension below Δmax, one can calculate the low-energy spectrum, parametrically to an accuracy of e−Δmax (although the precise accuracy depends on the state). Choosing Δmax = 9.5 we find very good agreement with the known spectrum obtained earlier by numerical DLCQ methods. Specifically, below the first three-particle threshold, we are able to identify all six single-particle bound-states, as well as several two-particle thresholds.
118161188
Higgs mass naturalness and scale invariance in the UV
It has been suggested that electroweak symmetry breaking in the Standard Model may be natural if the Standard Model merges into a conformal field theory (CFT) at short distances. In such a scenario the Higgs mass would be protected from quantum corrections by the scale invariance of the CFT. In order for the Standard Model to merge into a CFT at least one new ultraviolet (UV) scale is required at which the couplings turn over from their usual Standard Model running to the fixed point behavior. We argue that the Higgs mass is sensitive to such a turn-over scale even if there are no associated massive particles and the scale arises purely from dimensional transmutation. We demonstrate this sensitivity to the turnover scale explicitly in toy models. Thus if scale invariance is responsible for Higgs mass naturalness, then the transition to CFT dynamics must occur near the TeV scale with observable consequences at colliders. In addition, the UV fixed point theory in such a scenario must be interacting because logarithmic running near a free fixed point constitutes hard breaking of scale invariance and spoils the Higgs mass protection.
30185395
Structural characterization of the intramolecular interaction between the SH3 and guanylate kinase domains of PSD-95.
PSD-95/SAP90 is a member of the MAGUK superfamily. In excitatory synapses, PSD-95 clusters receptors and ion channels at specific sites in the postsynaptic membrane and organizes downstream signaling and cytoskeletal molecules. We have determined the crystal structures of the apo and GMP-bound forms to 2.3 and 2.0 A resolutions, respectively, of a fragment containing the SH3, HOOK, and guanylate kinase (GK) domains of PSD-95. We observe an intramolecular interaction between the SH3 and GK domains involving the formation of a beta sheet including residues N- and C-terminal to the GK domain. Based on amino acid conservation and mutational data available in the literature, we propose that this intramolecular interaction is a common feature among MAGUK proteins.