Deconfined quantum critical points: symmetries and dualities

The deconfined quantum critical point (QCP), separating the N\'eel and valence bond solid phases in a 2D antiferromagnet, was proposed as an example of $2+1$D criticality fundamentally different from standard Landau-Ginzburg-Wilson-Fisher {criticality}. In this work we present multiple equivalent descriptions of deconfined QCPs, and use these to address the possibility of enlarged emergent symmetries in the low energy limit. The easy-plane deconfined QCP, besides its previously discussed self-duality, is dual to $N_f = 2$ fermionic quantum electrodynamics (QED), which has its own self-duality and hence may have an O(4)$\times Z_2^T$ symmetry. We propose several dualities for the deconfined QCP with ${\mathrm{SU}(2)}$ spin symmetry which together make natural the emergence of a previously suggested $SO(5)$ symmetry rotating the N\'eel and VBS orders. These emergent symmetries are implemented anomalously. The associated infra-red theories can also be viewed as surface descriptions of 3+1D topological paramagnets, giving further insight into the dualities. We describe a number of numerical tests of these dualities. We also discuss the possibility of "pseudocritical" behavior for deconfined critical points, and the meaning of the dualities and emergent symmetries in such a scenario.Comment: Published version, 44 pages + references, 4 figures. A summary of main results in p7-

Uncorrelated Measurements of the Cosmic Expansion History and Dark Energy from Supernovae

We present a method for measuring the cosmic expansion history H(z) in uncorrelated redshift bins, and apply it to current and simulated type Ia supernova data assuming spatial flatness. If the matter density parameter Omega_m can be accurately measured from other data, then the dark energy density history X(z)=rho_X(z)/rho_X(0) can trivially be derived from this expansion history H(z). In contrast to customary ``black box'' parameter fitting, our method is transparent and easy to interpret: the measurement of H(z)^{-1} in a redshift bin is simply a linear combination of the measured comoving distances for supernovae in that bin, making it obvious how systematic errors propagate from input to output. We find the Riess et al. (2004) ``gold'' sample to be consistent with the ``vanilla'' concordance model where the dark energy is a cosmological constant. We compare two mission concepts for the NASA/DOE Joint Dark Energy Mission (JDEM), the Joint Efficient Dark-energy Investigation (JEDI), and the Supernova Accelaration Probe (SNAP), using simulated data including the effect of weak lensing (based on numerical simulations) and a systematic bias from K-corrections. Estimating H(z) in seven uncorrelated redshift bins, we find that both provide dramatic improvements over current data: JEDI can measure H(z) to about 10% accuracy and SNAP to 30-40% accuracy.Comment: 7 pages, 4 color figures. Expanded and revised version; PRD in pres

Macrophage Migration Inhibitory Factor Polymorphisms And Tuberculosis Disease Susceptibility In Kwazulu-Natal, South Africa

Background: TB is a leading cause of mortality, infecting over one-third of the world’s population. Difficulties combating the disease are compounded by the fact that a majority of TB infections remain in an asymptomatic latent state. Macrophage migration inhibitory factor (MIF) is an innate cytokine that is encoded in a functionally polymorphic genetic locus with characterized allelic variants that correlate to TB progression. Understanding the genetic factors that regulate host immune responses to TB will help to identify individuals who are at higher risk of severe infection. Methods: A case-control study of HIV+ active pulmonary TB cases and HIV+ controls with no history of active TB was conducted on a South African cohort. With informed consent, we obtained demographics, clinical information, and blood samples for determination of MIF promoter polymorphisms: a functional -794 CATT5-8 microsatellite, and a closely associated -173 G/C SNP. Serum cytokine levels were quantified using ELISA. Results: Among 165 enrolled patients (100 cases, 65 controls), 79 were female (40 cases, 39 controls). Aggregate polymorphism assessment revealed non-significant distribution differences between cases and controls for both the 794 CATT5-8 (p = 0.3316) and -173 G/C (p = 0.7452) loci. However, stratification by gender reveals a near significant difference in the frequency of CATT5/5 (p-value = 0.0863) and -173 G/G (p-value = 0.0949) low expresser genotypes in female cases versus controls but not in males. ELISA showed a significant difference (P = 0.0056) in serum cytokine levels between cases and controls but not between different polymorphisms. Conclusions: The results from this study suggest that MIF polymorphisms might contribute to susceptibility to TB in a sex-dependent manner and that MIF low-expresser genotypes might confer higher risk for active TB. However, additional studies will need to be done to establish this relationship

PABO: Mitigating Congestion via Packet Bounce in Data Center Networks

In today's data center, a diverse mix of throughput-sensitive long flows and delay-sensitive short flows are commonly presented in shallow-buffered switches. Long flows could potentially block the transmission of delay-sensitive short flows, leading to degraded performance. Congestion can also be caused by the synchronization of multiple TCP connections for short flows, as typically seen in the partition/aggregate traffic pattern. While multiple end-to-end transport-layer solutions have been proposed, none of them have tackled the real challenge: reliable transmission in the network. In this paper, we fill this gap by presenting PABO -- a novel link-layer design that can mitigate congestion by temporarily bouncing packets to upstream switches. PABO's design fulfills the following goals: i) providing per-flow based flow control on the link layer, ii) handling transient congestion without the intervention of end devices, and iii) gradually back propagating the congestion signal to the source when the network is not capable to handle the congestion.Experiment results show that PABO can provide prominent advantage of mitigating transient congestions and can achieve significant gain on end-to-end delay