Genus Topology of the Cosmic Microwave Background from the WMAP 3-Year Data

We have independently measured the genus topology of the temperature fluctuations in the cosmic microwave background seen in the Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data. A genus analysis of the WMAP data indicates consistency with Gaussian random-phase initial conditions, as predicted by standard inflation. We set 95% confidence limits on non-linearities of -101 < f_{nl} < 107. We also find that the observed low l (l <= 8) modes show a slight anti-correlation with the Galactic foreground, but not exceeding 95% confidence, and that the topology defined by these modes is consistent with that of a Gaussian random-phase distribution (within 95% confidence).Comment: MNRAS LaTeX style (mn2e.cls), EPS and JPEG figure

States near Dirac points of rectangular graphene dot in a magnetic field

In neutral graphene dots the Fermi level coincides with the Dirac points. We have investigated in the presence of a magnetic field several unusual properties of single electron states near the Fermi level of such a rectangular-shaped graphene dot with two zigzag and two armchair edges. We find that a quasi-degenerate level forms near zero energy and the number of states in this level can be tuned by the magnetic field. The wavefunctions of states in this level are all peaked on the zigzag edges with or without some weight inside the dot. Some of these states are magnetic field-independent surface states while the others are field-dependent. We have found a scaling result from which the number of magnetic field-dependent states of large dots can be inferred from those of smaller dots.Comment: Physical review B in pres

Regularization, Renormalization and Range: The Nucleon-Nucleon Interaction from Effective Field Theory

Regularization and renormalization is discussed in the context of low-energy effective field theory treatments of two or more heavy particles (such as nucleons). It is desirable to regulate the contact interactions from the outset by treating them as having a finite range. The low energy physical observables should be insensitive to this range provided that the range is of a similar or greater scale than that of the interaction. Alternative schemes, such as dimensional regularization, lead to paradoxical conclusions such as the impossibility of repulsive interactions for truly low energy effective theories where all of the exchange particles are integrated out. This difficulty arises because a nonrelativistic field theory with repulsive contact interactions is trivial in the sense that the $S$ matrix is unity and the renormalized coupling constant zero. Possible consequences of low energy attraction are also discussed. It is argued that in the case of large or small scattering lengths, the region of validity of effective field theory expansion is much larger if the contact interactions are given a finite range from the beginning.Comment: 7 page

Remarks on the Scalar Graviton Decoupling and Consistency of Horava Gravity

Recently Horava proposed a renormalizable gravity theory with higher derivatives by abandoning the Lorenz invariance in UV. But there have been confusions regarding the extra scalar graviton mode and the consistency of the Horava model. I reconsider these problems and show that, in the Minkowski vacuum background, the scalar graviton mode can be consistency decoupled from the usual tensor graviton modes by imposing the (local) Hamiltonian as well as the momentum constraints.Comment: Some clarifications regarding the projectable case added, Typos corrected, Comments (Footnote No.9, Note Added) added, References updated, Accepted in CQ

Diffuse Dark and Bright Objects in the Hubble Deep Field

In the Hubble Deep Field (HDF) we have identified candidate regions where primordial galaxies might be forming. These regions are identified from negative or positive peaks in the difference maps obtained from the HDF maps smoothed over 0.8'' and 4''. They have apparent V magnitudes typically between 29 and 31 (missing flux below the local average level for the dark objects). The identified objects are shown to be real by two ways. First, the cross-correlations of these peaks detected in different filters are strong. Second, their auto-correlation functions indicate that these faint diffuse objects are self-clustered. The subset of objects dark in the F450W and F606W bandpasses, but bright in F814W, also shows stronger correlation compared to the whole dark sample. This further supports that our samples are indeed physical objects. The amplitude and slope of the angular correlation function of the bright objects indicates that these objects are ancestors of the present nearby bright galaxies. We have inspected individual bright objects and noted that they have several tiny spots embedded in extended backgrounds. They are likely to be the primordial galaxies at high redshifts in the process of active star formation and merging. Our subset of dark objects is thought to be the `intergalactic dark clouds' he blocking the background far UV light (at the rest frame) at high redshifts instead of empty spaces between the first galaxies at the edge of the universe of galaxies.Comment: ApJ, submitted.10 pages including 8 figures(1 large postscript figure file) uses kjhantwo.sty .Also available at http://astro.snu.ac.kr/preprint1997.htm

New attractor mechanism for spherically symmetric extremal black holes

We introduce a new attractor mechanism to find the entropy for spherically symmetric extremal black holes. The key ingredient is to find a two-dimensional (2D) dilaton gravity with the dilaton potential $V(\phi)$. The condition of an attractor is given by $\nabla^2\phi=V(\phi_0)$ and $\bar{R}_2=-V^{\prime}(\phi_0)$ and for a constant dilaton $\phi=\phi_0$, these are also used to find the location of the degenerate horizon $r=r_{e}$ of an extremal black hole. As a nontrivial example, we consider an extremal regular black hole obtained from the coupled system of Einstein gravity and nonlinear electrodynamics. The desired Bekenstein-Hawking entropy is successfully recovered from the generalized entropy formula combined with the 2D dilaton gravity, while the entropy function approach does not work for obtaining this entropy.Comment: 20 pages, 4 figures, Accepted for publication in Physical Review D. This version includes revisions suggested by the refere