Can effects of quantum gravity be observed in the cosmic microwave background?

We investigate the question whether small quantum-gravitational effects can be observed in the anisotropy spectrum of the cosmic microwave background radiation. An observation of such an effect is needed in order to discriminate between different approaches to quantum gravity. Using canonical quantum gravity with the Wheeler-DeWitt equation, we find a suppression of power at large scales. Current observations only lead to an upper bound on the energy scale of inflation, but the framework is general enough to study other situations in which such effects might indeed be seen.Comment: 5 pages, 1 figure, essay awarded first prize in the Gravity Research Foundation essay competition 201

Properties of cryogenically worked metals

A program was conducted to determine whether the mechanical properties of cryogenically worked 17-7PH stainless steel are suitable for service from ambient to cryogenic temperatures. It was determined that the stress corrosion resistance of the cryo-worked material is quite adequate for structural service. The tensile properties and fracture toughness at room temperature were comparable to titanium alloy 6Al-4V. However, at cryogenic temperatures, the properties were not sufficient to recommend consideration for structural service

Comments on Critical Electric and Magnetic Fields from Holography

We discuss some aspects of critical electric and magnetic fields in a field theory with holographic dual description. We extend the analysis of arxiv:1109.2920, which finds a critical electric field at which the Schwinger pair production barrier drops to zero, to the case of magnetic fields. We first find that, unlike ordinary weakly coupled theories, the magnetic field is not subject to any perturbative instability originating from the presence of a tachyonic ground state in the W-boson spectrum. This follows from the large value of the 't Hooft coupling \lambda, which prevents the Zeeman interaction term to overcome the particle mass at high B. Consequently, we study the next possible B-field instability, i.e. monopole pair production, which is the S-dual version of the Schwinger effect. Also in this case a critical magnetic field is expected when the tunneling barrier drops to zero. These Schwinger-type criticalities are the holographic duals, in the bulk, to the fields E or B reaching the tension of F1 or D1 strings respectively. We then discuss how this effect is modified when electric and magnetic fields are present simultaneously and dyonic states in the spectrum can be pair produced by a generic E - B background. Finally, we analyze finite temperature effects on Schwinger criticalities, i.e. in the AdS-Schwarzshild black hole background.Comment: 33 pages, 4 figures; v2: refs added; v3: typos corrected, to appear on JHE

What can quantum cosmology say about the inflationary universe?

We propose a method to extract predictions from quantum cosmology for inflation that can be confronted with observations. Employing the tunneling boundary condition in quantum geometrodynamics, we derive a probability distribution for the inflaton field. A sharp peak in this distribution can be interpreted as setting the initial conditions for the subsequent phase of inflation. In this way, the peak sets the energy scale at which the inflationary phase has started. This energy scale must be consistent with the energy scale found from the inflationary potential and with the scale found from a potential observation of primordial gravitational waves. Demanding a consistent history of the universe from its quantum origin to its present state, which includes decoherence, we derive a condition that allows one to constrain the parameter space of the underlying model of inflation. We demonstrate our method by applying it to two models: Higgs inflation and natural inflation.Comment: 13 pages, 2 figures. Contribution to the Proceedings of the DICE14 meeting, Castiglioncello, September 201

Quantum cosmological consistency condition for inflation

We investigate the quantum cosmological tunneling scenario for inflationary models. Within a path-integral approach, we derive the corresponding tunneling probability distribution. A sharp peak in this distribution can be interpreted as the initial condition for inflation and therefore as a quantum cosmological prediction for its energy scale. This energy scale is also a genuine prediction of any inflationary model by itself, as the primordial gravitons generated during inflation leave their imprint in the B-polarization of the cosmic microwave background. In this way, one can derive a consistency condition for inflationary models that guarantees compatibility with a tunneling origin and can lead to a testable quantum cosmological prediction. The general method is demonstrated explicitly for the model of natural inflation.Comment: 1+16 pages, 3 figures. v2: typos corrected, minor improvement of the discussio

Measurement Theory and General Relativity

The theory of measurement is employed to elucidate the physical basis of general relativity. For measurements involving phenomena with intrinsic length or time scales, such scales must in general be negligible compared to the (translational and rotational) scales characteristic of the motion of the observer. Thus general relativity is a consistent theory of coincidences so long as these involve classical point particles and electromagnetic rays (geometric optics). Wave optics is discussed and the limitations of the standard theory in this regime are pointed out. A nonlocal theory of accelerated observers is briefly described that is consistent with observation and excludes the possibility of existence of a fundamental scalar field in nature.Comment: LaTeX springer style lamu.cls, 2 figures, 16 pages, published in: Black Holes: Theory and Observation: Proceedings of the 179th W.E. Heraeus Seminar, held August 1997 in Bad Honnef, Germany. F.W. Hehl et al.(eds). (Springer, Berlin Heidelberg 1998

Crogenic alloy screening Interim report

Evaluation of mechanical properties and fracture strength of aluminum alloys and stainless stee

Determination of low-temperature fatigue properties of structural metal alloys Final report, Jul. 1964 - Aug. 1965

Fatigue testing and determination of low temperature properties of structural metal alloys - aluminum alloy, stainless steel, and nickel alloy