17,910 research outputs found
The complex plank problem
It is shown that if is a sequence of norm in a complex Hilbert space and is a sequence of nonnegative numbers satisfying
then there is a unit vector z for which
$|\langle v_{j}, z \rangle|\geq t_{j}
for every j. The result is a strong, complex analogue of the author's real plank theorem
CDT and the Big Bang
We describe a CDT-like model where breaking of W3 symmetry will lead to the
emergence of time and subsequently of space. Surprisingly the simplest such
models which lead to higher dimensional spacetimes are based on the four
"magical" Jordan algebras of 3x3 Hermitian matrices with real, complex,
quaternion and octonion entries, respectively. The simplest symmetry breaking
leads to universes with spacetime dimensions 3, 4, 6, and 10
Cosmological Models and Renormalization Group Flow
We study cosmological solutions of Einstein gravity with a positive
cosmological constant in diverse dimensions. These include big-bang models that
re-collapse, big-bang models that approach de Sitter acceleration at late
times, and bounce models that are both past and future asymptotically de
Sitter. The re-collapsing and the bounce geometries are all tall in the sense
that entire spatial slices become visible to a comoving observer before the end
of conformal time, while the accelerating big-bang geometries can be either
short or tall. We consider the interpretation of these cosmological solutions
as renormalization group flows in a dual field theory and give a geometric
interpretation of the associated c-function as the area of the apparent
cosmological horizon in Planck units. The covariant entropy bound requires
quantum effects to modify the early causal structure of some of our big-bang
solutions.Comment: 26 pages, 11 figures, v2: improved discussion of entropy bounds,
references added, v3: minor changes, reference adde
Hot big bang or slow freeze?
We confront the big bang for the beginning of the universe with an equivalent
picture of a slow freeze - a very cold and slowly evolving universe. In the
freeze picture the masses of elementary particles increase and the
gravitational constant decreases with cosmic time, while the Newtonian
attraction remains unchanged. The freeze and big bang pictures both describe
the same observations or physical reality. We present a simple "crossover
model" without a big bang singularity. In the infinite past space-time is flat.
Our model is compatible with present observations, describing the generation of
primordial density fluctuations during inflation as well as the present
transition to a dark energy dominated universe.Comment: new material on absence of singularity, 9 pages, 1 figur
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