Topology and chiral symmetry breaking in SU(Nc ) gauge theories
Physical Review D 66:9 (2002)
Abstract:
We study the low-lying eigenmodes of the lattice overlap Dirac operator for SV(Nc) gauge theories with Nc=2, 3, 4 and 5 colors. We define a fermionic topological charge from the zero modes of this operator and show that, as Nc grows, any disagreement with the topological charge obtained by cooling the fields becomes rapidly less likely. By examining the fields where there is a disagreement, we are able to show that the Dirac operator does not resolve instantons below a critical size of about ρ≃2.5a, but resolves the larger, more physical instantons. We investigate the local chirality of the near-zero modes and how it changes as we go to larger Nc. We observe that the local chirality of these modes, which is prominent for SU(2) and SU(3), becomes rapidly weaker for larger N c and is consistent with disappearing entirely in the limit of N c = ∞. We find that this is not simply due to the observed disappearance of small instantons at larger Nc. © 2002 The American Physical Society.
A reconstruction of the initial conditions of the Universe by optimal mass transportation
Nature, 2022, Volume 417, Issue 6886, pp. 260-262
Abstract:
Reconstructing the density fluctuations in the early Universe that evolved into the distribution of galaxies we see today is a challenge to modern cosmology. An accurate reconstruction would allow us to test cosmological models by simulating the evolution starting from the reconstructed primordial state and comparing it to observations. Several reconstruction techniques have been proposed, but they all suffer from lack of uniqueness because the velocities needed to produce a unique reconstruction usually are not known. Here we show that reconstruction can be reduced to a well-determined problem of optimization, and present a specific algorithm that provides excellent agreement when tested against data from N-body simulations. By applying our algorithm to the redshift surveys now under way, we will be able to recover reliably the properties of the primeval fluctuation field of the local Universe, and to determine accurately the peculiar velocities (deviations from the Hubble expansion) and the true positions of many more galaxies than is feasible by any other method.
Big-bang nucleosynthesis (New)
(2002)
Cosmological Parameters and the Baryon Density from CMB and Galaxy Fluctuations
Astrophysics and Space Science Library Springer Nature 274 (2002) 303-308
Could the end be in sight for ultrahigh-energy cosmic rays?
PHYSICS WORLD 15:9 (2002) 23-24