Artículos con la etiqueta ‘High Energy Astrophysical Phenomena (astro-ph.HE)’

Is the CMB telling us that dark matter is weaker than weakly interacting?

Por • 9 jul, 2013 • Category: Leyes

If moduli, or other long-lived heavy states, decay in the early universe in part into light and feebly interacting particles (such as axions), these decay products could account for the additional energy density in radiation that is suggested by recent measurements of the CMB. These moduli decays will also, however, alter the expansion history of the early universe, potentially diluting the thermal relic abundance of dark matter. If this is the case, then dark matter particles must annihilate with an even lower cross section than required in the standard thermal scenario (sigma v < 3×10^-26 cm^3/s) if they are to make up the observed density of dark matter. This possibility has significant implications for direct and indirect searches for dark matter.



The most powerful particles in the Universe: a cosmic smash

Por • 9 may, 2013 • Category: Crítica

This year we are celebrating 101 years since the discovery of cosmic rays. They are whizzing all around the Universe, and they occur at very different energies, including the highest particle energies that exist. However, theory predicts an abrupt suppression (a «cutoff») above a specific huge energy. This is difficult to verify, the measurements are controversial, but it provides a unique opportunity to probe established concepts of physics – like Lorentz Invariance – under extreme conditions. If the observations will ultimately contradict this «cutoff», this could require a fundamental pillar of physics to be revised.



Constraints on the Universe as a Numerical Simulation

Por • 27 dic, 2012 • Category: Opinion

Observable consequences of the hypothesis that the observed universe is a numerical simulation performed on a cubic space-time lattice or grid are explored. The simulation scenario is first motivated by extrapolating current trends in computational resource requirements for lattice QCD into the future. Using the historical development of lattice gauge theory technology as a guide, we assume that our universe is an early numerical simulation with unimproved Wilson fermion discretization and investigate potentially-observable consequences. Among the observables that are considered are the muon g-2 and the current differences between determinations of alpha, but the most stringent bound on the inverse lattice spacing of the universe, b^(-1) >~ 10^(11) GeV, is derived from the high-energy cut off of the cosmic ray spectrum. The numerical simulation scenario could reveal itself in the distributions of the highest energy cosmic rays exhibiting a degree of rotational symmetry breaking that reflects the structure of the underlying lattice.