arXiv subjects
Publications and source records attributed to W. Fischler.
We argue that the correlation between the modular Hamiltonians of two causal diamonds related by a finite time translation is equal to the uncertainty in the modular Hamiltonian of the diamond in their overlap. In a separate section we investigate the relation between entropy fluctuations in a diamond, and length fluctuations calculated from the 't Hooft commutation relations.
The Holographic Space-time (HST) model of inflation has a potential explanation for dark matter as tiny primordial black holes. Motivated by a recent paper of Barrau\cite{barrau} we propose a version of this model where some of the Inflationary Black Holes (IBHs), whose decay gives rise to the Hot Big Bang, carry the smallest value of a discrete symmetry charge. The fraction $f$ of IBHs carrying this charge is difficult to estimate from first principles, but we fix it by requiring that the crossover between radiation and matter domination occurs at the correct temperature $T_{eq} \sim 1 eV = 10^{-28} M_P$. The fraction is small, $f \sim 2\times 10^{-9}$ so we believe this gives an extremely plausible model of dark matter.
This essay outlines the Holographic Space-time (HST) theory of cosmology and its relation to conventional theories of inflation. The predictions of the theory are compatible with observations, and one must hope for data on primordial gravitational waves or non-Gaussian fluctuations to distinguish it from conventional models. The model predicts an early era of structure formation, prior to the Big Bang. Understanding the fate of those structures requires complicated simulations that have not yet been done. The result of those calculations might falsify the model, or might provide a very economical framework for explaining dark matter and the generation of the baryon asymmetry.
We use the formalisms of Holographic Space-time (HST) and Matrix Theory[11] to investigate the claim of [1] that old black holes contain a firewall, i.e. an in-falling detector encounters highly excited states at a time much shorter than the light crossing time of the Schwarzschild radius. In both formalisms there is no dramatic change in particle physics inside the horizon until a time of order the Schwarzschild radius. The Matrix Theory formalism has been shown to give rise to an S-matrix, which coincides with effective supergravity for an infinite number of low energy amplitudes. We conclude that the firewall results from an inappropriate use of quantum effective field theory to describe fine details of localized events near a black hole horizon. In both HST and Matrix Theory, the real quantum gravity Hilbert space in a localized region contains many low energy degrees of freedom that are not captured in QU(antum) E(ffective) F(ield) T(heory) and omits many of the high energy DOF in QUEFT.
We use the formalism of Holographic Space-time (HST) to investigate the claim of [1] that old black holes contain a firewall, i.e. an in-falling observer encounters highly excited states at a time much shorter than the light crossing time of the Schwarzschild radius. This conclusion is much less dramatic in HST than in the hypothetical models of quantum gravity used in [1]. In HST there is no dramatic change in particle physics inside the horizon until a time of order the Schwarzschild radius.
We generalize to string theory a construction, originally proposed in field theory, that generates a hierarchy in the splittings between members of super-multiplets in various sectors of the theory.
We explore how to generate hierarchies in the splittings between superpartners. Some of the consequences are the existence of invisible components of dark matter, new inflaton candidates, invisible monopoles and a number of invisible particles that might dominate during various eras, in particular between BBN and recombination and decay subsequently.
We study the growth of perturbations in an expanding Bianchi type-I metric that evolves according to an energy density that includes dust and a cosmological constant. Assuming an epoch where the cosmological constant is subdominant, we find that, for a reasonably large set of initial conditions, the metric fluctuations grow fast enough to make the metric inhomogeneous before the cosmological constant becomes the dominant form of energy. We have examined values for the cosmological constant that are in the interval $10^{10} {GeV}$ to $10^{16} {GeV}$.
We examine recent claims for a considerable amount of leptogenesis, in some inflationary scenarios, through the gravitational anomaly in the lepton number current. We find that when the short distances contributions are properly included the amount of lepton number generated is actually much smaller.
We conjecture that space-like singularities are simply regions in which all available degrees of freedom are excited, and the system cycles randomly through generic quantum states in its Hilbert space. There is no simple geometric description of the interior of such a region, but if it is embedded in a semi-classical space-time an external observer sees it as a black hole. Big Bang and Crunch singularities, for which there is no such embedding, must be described in purely quantum terms. We present several possible descriptions of such cosmologies.
dS/CFT gives a perturbatively gauge invariant definition of particle masses in de Sitter (dS) space. We show, in a toy model in which the graviton is replaced with a minimally coupled massless scalar field, that loop corrections to these masses are infrared (IR) divergent. We argue that this implies anomalous dependence of masses on the cosmological constant, in a true theory of quantum gravity. This is in accord with the hypothesis of Cosmological SUSY Breaking (CSB).
We review the successes and challenges of the holographic approach to cosmology. The model predicts an exactly scale invariant fluctuation spectrum with long and short distance cut-offs. It can account for the observed fluctuations in the CMB and might explain the low power at large scales. We outline various cosmological histories compatible with holographic initial conditions. This paper is based on talks given by the authors at Cosmo 04 in Toronto, and the 2004 Tamura Symposium in Austin
We present a complete quantum mechanical description of a flat FRW universe with equation of state p=ρ. We find a detailed correspondence with our heuristic picture of such a universe as a dense black hole fluid. Features of the geometry are derived from purely quantum input.
The observational limits on the present energy density of the Universe allow for a component that redshifts like $1/a^2$ and can contribute significantly to the total. We show that a possible origin for such a contribution is that the universe has a toroidal topology with "wound" scalar fields around its cycles.
We describe a cosmology of the very early universe, based on the holographic principle of 't Hooft and Susskind. We have described the initial state as a dense black hole fluid. Here we present a mathematical model of this heuristic picture, as well as a non-rigorous discussion of how a more normal universe could evolve out of such a state. The gross features of the cosmology depend on a few parameters, which cannot yet be calculated from first principles. For some range of these parameters, microwave background fluctuations originate from fluctuations in the black hole fluid, and have characteristics different from those of most inflationary models.
If the present acceleration of the universe is due to an asymptotically de Sitter universe with small cosmological constant, and the principle of Cosmological Complementarity is valid, then the number of e-foldings during inflation is bounded.
We present a new version of holographic cosmology, which is compatible with present observations. A primordial $p=ρ$ phase of the universe is followed by a brief matter dominated era and a brief period of inflation, whose termination heats the universe. The flatness and horizon problems are solved by the $p=ρ$ dynamics. The model is characterized by two parameters, which should be calculable in a more fundamental approach to the theory. For a large range in the phenomenologically allowed parameter space, the observed fluctuations in the cosmic microwave background were generated during the $p=ρ$ era, and are exactly scale invariant. The scale invariant spectrum cuts off sharply at both upper and lower ends, and this may have observational consequences. We argue that the amplitude of fluctuations is small but cannot yet calculate it precisely.
If the present acceleration of the universe is due to a cosmological constant, λ, then the entropy of the microwave background is bounded. It cannot exceed λ^{-3/4} \sim 10^{91}, which is much less than the entropy of empty de Sitter space λ^{-1} \sim 10^{122}. This is due to the limited efficiency of storing entropy by local field theoretical degrees of freedom. The observed entropy of the microwave background is of O(10^{85}).