## Events at Physics |

### Events on Friday, February 26th, 2010

**NPAC (Nuclear/Particle/Astro/Cosmo) Forum****Joint with Phenomenology****Comprehensive Solution to the Cosmological Constant, Zero-Point Energy, and Quantum Gravity Problems****Time:**2:30 pm**Place:**5280 Chamberlin**Speaker:**Philip Mannheim, University of Connecticut**Abstract:**We present a solution to the cosmological constant, the zero-point energy, and the quantum gravity problems within a single comprehensive framework.We show that in quantum theories of gravity in which the zero-point energy density of the gravitational field is well-defined, the cosmological

constant and zero-point energy problems solve each other by mutual

cancellation between the cosmological constant and the matter and

gravitational field zero-point energy densities. Because of this

cancellation, regulation of the matter field zero-point energy density is not needed, and thus does not cause any trace anomaly to arise. We exhibit our results in two theories of gravity that are well-defined quantum-mechanically. Both of these theories are locally conformal invariant, quantum Einstein gravity in two dimensions and Weyl-tensor-based quantum conformal gravity in four dimensions (a fourth-order derivative quantum theory of the type that Bender and Mannheim have recently shown to be ghost-free and unitary). Central to our approach is the requirement that any and all departures of the geometry from Minkowski are to be brought about by quantum mechanics alone. Consequently, there have to be no fundamental classical fields, and all mass scales have to be generated by dynamical condensates. In such a situation the trace of the matter field energy-momentum tensor is zero, a constraint that obliges its cosmological constant and zero-point contributions to cancel each other identically, no matter how large they might be. Quantization of the gravitational field is caused by its coupling to quantized matter fields, with the gravitational field not needing any independent quantization of its own. With there being no a priori classical curvature, one does not have to make it compatible with quantization.**Physics Department Colloquium****Special Joint Physics/Astronomy Colloquium Talk****Confronting the Dark Energy Crisis in Fundamental Physics****Time:**4:00 pm**Place:**2241 Chamberlin Hall (coffee at 3:30 pm)**Speaker:**Christopher Stubbs, Harvard University, Physics and Astronomy**Abstract:**The best evidence we currently have for physics beyond the standard model comes from astrophysical observations: Dark Energy (repulsive gravity in the vacuum!) , Dark Matter (ordinary matter is a minority component of the mass budget of the Universe), and even the cosmic abundance of matter over antimatter are each indications of shortcomings in our understanding of basic physics. I will describe our efforts to understand the nature of the Dark Energy, and why this particular problem merits our collective attention. I'll also present the status of PanSTARRS and the Large Synoptic Survey Telescope (LSST), two ambitious ground-based optical systems that will provide new capabilities for studying diverse topics in astronomy and astrophysics, and fundamental physics.**Host:**Karsten Heeger