Philosophical Implications of Inflationary Cosmology

Recent developments in cosmology indicate that every history having a nonzero probability is realized in infinitely many distinct regions of spacetime. Thus, it appears that the universe contains infinitely many civilizations exactly like our own, as well as infinitely many civilizations that differ from our own in any way permitted by physical laws. We explore the implications of this conclusion for ethical theory and for the doomsday argument. In the infinite universe, we find that the doomsday argument applies only to effects which change the average lifetime of all civilizations, and not those which affect our civilization alone.Comment: 25 pages; v2: revised version to appear in British Journal for the Philosophy of Scienc

Reionization from cosmic string loops

Loops formed from a cosmic string network at early times would act as seeds for early formation of halos, which would form galaxies and lead to early reionization. With reasonable guesses about astrophysical and string parameters, the cosmic string scale $G\mu$ must be no more than about $3\times 10^{-8}$ to avoid conflict with the reionization redshift found by WMAP. The bound is much stronger for superstring models with a small string reconnection probability. For values near the bound, cosmic string loops may explain the discrepancy between the WMAP value and theoretical expectations.Comment: 7 pp., RevTeX, no figure

Scaling of cosmic string loops

We study the spectrum of loops as a part of a complete network of cosmic strings in flat spacetime. After a long transient regime, characterized by production of small loops at the scale of the initial conditions, it appears that a true scaling regime takes over. In this final regime the characteristic length of loops scales as $0.1 t$, in contrast to earlier simulations which found tiny loops. We expect the expanding-universe behavior to be qualitatively similar. The large loop sizes have important cosmological implications. In particular, the nucleosynthesis bound becomes $G\mu \lesssim 10^{-7}$, much tighter than before.Comment: Added discussion of gravitational wave bounds; other minor change

Forward-Backward Asymmetry as a Discovery Tool for Z' Bosons at the LHC

The Forward-Backward Asymmetry (AFB) in Z' physics is commonly only perceived as the observable which possibly allows one to interpret a Z' signal by distinguishing different models of such (heavy) spin-1 bosons. In this paper, we examine the potential of AFB in setting bounds on or even discovering a Z' boson at the Large Hadron Collider (LHC) and show that it might be a powerful tool for this purpose. We analyse two different scenarios: Z' bosons with a narrow and wide width, respectively. We find that, in the first case, the significance of the AFB search can be comparable with that of the bump search usually adopted by the experimental collaborations; however, being a ratio of (differential) cross sections the AFB has the advantage of reducing systematical errors. In the second case, the AFB search can win over the bump search in terms of event shape, as the structure of the AFB distribution as a function of the invariant mass of the reconstructed Z'boson could nail down the new broad resonance much better than the event counting strategy usually adopted in such cases.Comment: 27 pages, 17 figure

Complementarity of Forward-Backward Asymmetry for discovery of Z' bosons at the Large Hadron Collider

The Forward-Backward Asymmetry (AFB) in Z' physics is commonly only thought of as an observable which possibly allows one to profiling a Z' signal by distinguishing different models embedding such (heavy) spin-1 bosons. In this brief review, we examine the potential of AFB in setting bounds on or even discovering a Z' at the Large Hadron Collider (LHC) and proof that it might be a powerful tool for this purpose. We analyse two different scenarios: Z's with a narrow and wide width, respectively. We find that, in both cases, AFB can complement the conventional searches in accessing Z' signals traditionally based on cross section measurements only.Comment: arXiv admin note: substantial text overlap with arXiv:1504.0316