8 research outputs found
Probabilities in the inflationary multiverse
Inflationary cosmology leads to the picture of a "multiverse," involving an
infinite number of (spatially infinite) post-inflationary thermalized regions,
called pocket universes. In the context of theories with many vacua, such as
the landscape of string theory, the effective constants of Nature are
randomized by quantum processes during inflation. We discuss an analytic
estimate for the volume distribution of the constants within each pocket
universe. This is based on the conjecture that the field distribution is
approximately ergodic in the diffusion regime, when the dynamics of the fields
is dominated by quantum fluctuations (rather than by the classical drift). We
then propose a method for determining the relative abundances of different
types of pocket universes. Both ingredients are combined into an expression for
the distribution of the constants in pocket universes of all types.Comment: 18 pages, RevTeX 4, 2 figures. Discussion of the full probability in
Sec.VI is sharpened; the conclusions are strengthened. Note added explaining
the relation to recent work by Easther, Lim and Martin. Some references adde
Probing reheating temperature of the universe with gravitational wave background
Thermal history of the universe after big-bang nucleosynthesis (BBN) is well
understood both theoretically and observationally, and recent cosmological
observations also begin to reveal the inflationary dynamics. However, the epoch
between inflation and BBN is scarcely known. In this paper we show that the
detection of the stochastic gravitational wave background around 1Hz provides
useful information about thermal history well before BBN. In particular, the
reheating temperature of the universe may be determined by future space-based
laser interferometer experiments such as DECIGO and/or BBO if it is around
10^{6-9} GeV, depending on the tensor-to-scalar ratio and dilution factor
.Comment: 20 pages, 8 figure
Modern tests of Lorentz invariance
Motivated by ideas about quantum gravity, a tremendous amount of effort over
the past decade has gone into testing Lorentz invariance in various regimes.
This review summarizes both the theoretical frameworks for tests of Lorentz
invariance and experimental advances that have made new high precision tests
possible. The current constraints on Lorentz violating effects from both
terrestrial experiments and astrophysical observations are presented.Comment: Modified and expanded discussions of various points. Numerous
references added. Version matches that accepted by Living Reviews in
Relativit
Quantum Spacetime Phenomenology
I review the current status of phenomenological programs inspired by
quantum-spacetime research. I stress in particular the significance of results
establishing that certain data analyses provide sensitivity to effects
introduced genuinely at the Planck scale. And my main focus is on
phenomenological programs that managed to affect the directions taken by
studies of quantum-spacetime theories.Comment: 125 pages, LaTex. This V2 is updated and more detailed than the V1,
particularly for quantum-spacetime phenomenology. The main text of this V2 is
about 25% more than the main text of the V1. Reference list roughly double
The origin of the universe as revealed through the polarization of the cosmic microwave background
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The Origin of the Universe as Revealed Through the Polarization of the Cosmic Microwave Background
Modern cosmology has sharpened questions posed for millennia about the origin of our cosmic habitat. The age-old questions have been transformed into two pressing issues primed for attack in the coming decade:
• How did the Universe begin?
The current cosmological paradigm successfully explains how the majestic structure observed in the Universe today grew out of small ripples in the density of matter. What is the physical origin of the primordial seeds which are ultimately responsible for the existence of galaxies, stars, planets, and people in the Universe? It is natural to expect (and many theories predict) that whatever produced the density ripples also produced gravity waves – undulations in the fabric of space-time which travel at the speed of light. Does the Universe contain a spectrum of primordial gravity waves produced by the same mechanism which produced the ripples in the density?
• What physical laws govern the Universe at the highest energies?
All explanations for the seeds of structure rely on physics at energies far beyond those probed by, e.g., CERN’s Large Hadron Collider. Experiments probing these seeds therefore may provide information about new particles, forces, or perhaps even extra dimensions of space that are visible only at the highest energies.
The clearest window onto these questions is the pattern of polarization in the Cosmic Microwave Background (CMB), which is uniquely sensitive to primordial gravity waves. A detection of the special pattern produced by gravity waves would be not only an unprecedented discovery, but also a direct probe of physics at the earliest observable instants of our Universe. Experiments which map CMB polarization over the coming decade will lead us on our first steps towards answering these age-old questions.Astronom