This Proposal addresses the question of how we would experimentally determine that our universe is a 3+1 dimensional brane (membrane) embedded in a higher dimensional space-time. The degrees of freedom that are localized on a flexible brane world generically include four dimensional vector fields. The model independent presence of such brane vectors in physical models with extra-dimensions may in fact provide a first glimpse into the extra dimensions if the brane vectors are lighter than any of the degrees of freedom that can propagate directly into the bulk. The main purpose of the proposed project is to employ a four dimensional effective field theory that describes, to some extent in a universal way, the coupling of the Standard Model fields to the brane vectors in order to study how current and future accelerator experiments and astro-physical observations can be used to probe and constrain scenarios with extra dimensions. The principal investigator and his collaborators have already started an initial study of the brane vector phenomenology. The brane oscillation world volume massive vector (Proca) fields is denoted by X and has a mass MX and a bilinear coupling to the energy-momentuma tensor of the form MX^2/FX ^4 . Data from the lepton colliders LEP-I and LEP-II has been employed to give excluded and allowed regions for the MX-FX parameter space. In particular the annihilation of an electron and positron to produce a single photon and two brane vectors which escape the detector as missing energy is used to delineate the regions of this parameter space. Once LHC is operating the PI intends to use experimental data to map out allowed regions of M-F parameter space. The project will create valuable research training in the field of particle physics for undergraduate students. The PI also plans to give general talks on physics to alumni and staff at the College.

Project Report

The encompassing objective of this project was to develop a better understanding of particle physics at very small scales. The concrete results of the sponsored work can be divided into several categories: 1. Further insight was obtained into the way particles potentially associated with the oscillations of physical space-time into hypothesized extra dimensions (gravi-vectors) would manifest themselves in particle collider experiments. A model was constructed that describes the properties of gravi-vectors and their interactions with conventional elementary particles that are included in the Standard Model. The non-observation of gravi-vectors in collider experiments to date was translated into limits on the nature of the space-time oscillations. The discovery range for gravi-vectors at particle accelerator experiments planned for the future was outlined as well. The potential decay of the Higgs boson into pairs of gravi-vectors was also considered, and its implications for the search for the Higgs boson were determined. 2. An economical model that potentially provides simultaneous particle physics explanations for inflation (the rapid early expansion of the Universe thought to be the reason for its current homogeneous and isotropic state), electroweak symmetry breaking (the mechanism that gives particles mass) and dark matter (the inert matter that so far only has been observed through its gravitational interactions but appears to far dominate the familiar visible matter in the Universe) was investigated. In the model the Higgs field plays a double role; it is responsible for both inflation and electroweak symmetry breaking. The dark matter is minimally realized as just a single type of scalar particle that only interacts with the Higgs boson. The results of this investigation specify the relations between the masses and interactions of the Higgs boson and the dark matter particle that are required for this scenario to be consistent with current experimental data and observations. 3. An alternative to the supersymmetric extension of the Standard Model was explored. In this model some Higgs bosons are elementary while others are composite structures held together by a novel strong interaction. An effective theoretical framework encoding the dynamics of just the light particles was constructed and a preliminary survey of its potential implications for particle collider experiments was completed. The NSF funding for this project provided support for research at a primarily undergraduate institution. Due in part to this support the principal investigator was able to provide advanced training opportunities for undergraduate students in all aspects of scientific research. Integration of teaching and research provides a highly effective path to prepare and inspire undergraduate students for careers in science and technology. Participating in this research project has proven to be a very successful gateway for its undergraduate student participants to enter other research opportunities and graduate programs. An important further impact of this project beyond its direct scientific merit, in particular when it is viewed in aggregate with similar projects at other primarily undergraduate institutions, is thus the strengthening of the nation’s base in science and technology.

Agency
National Science Foundation (NSF)
Institute
Division of Physics (PHY)
Application #
0758073
Program Officer
Keith R. Dienes
Project Start
Project End
Budget Start
2008-06-01
Budget End
2012-05-31
Support Year
Fiscal Year
2007
Total Cost
$60,000
Indirect Cost
Name
Macalester College
Department
Type
DUNS #
City
Saint Paul
State
MN
Country
United States
Zip Code
55105