Renewal of Support for Short-range Tests of Gravity at Humboldt State University

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This award supports research in the Humboldt State University Gravitational Physics Laboratory (HSU GPL). Precision experiments will test the Weak Equivalence Principle (WEP) of General Relativity and the gravitational Inverse-Square Law (ISL) at unprecedented levels. The WEP will be tested at the millimeter scale and the ISL will be probed over sub-millimeter distances with unmatched sensitivity down to approximately 25 microns. In recent years the study of the gravitational interaction at short (sub-millimeter) distance scales has gained much attention due in a large part to unification scenarios arising in string or M-theory that require more than three spatial dimensions, some of which could be macroscopic. Short-range tests of gravity and the WEP also investigate possible proposed mechanisms that endeavor to explain the accelerated expansion of the universe, generally attributed to Dark Energy. Finally, such tests present the possibility to search for hypothetical new interactions due to exotic particles or other phenomena. Many scenarios concerning these effects predict a violation of the WEP or ISL at short distances. Since 1999, experimental limits have improved dramatically so that the ISL has proven valid over distances down to approximately 55 microns. A dedicated test of the WEP, however, has not been performed below the millimeter scale. The initial work described in this proposal will probe the WEP at the millimeter scale and below. This measurement will be accomplished with a parallel-plate torsion pendulum design that will provide an essentially null experiment and use multiple composition dipole combinations. Subsequently, a more difficult test of the gravitational ISL will be pursued by decreasing the pendulum/attractor mass separation to 100 microns. Humboldt State University is in a predominantly rural area of Northern California and the GPL is the only dedicated physics research laboratory in the Department of Physics and Astronomy. This award ensures that our undergraduates gain valuable research skills necessary for continuation of studies or pursuit of a career in industry. Undergraduates will also be sent to perform research at the University of Washington through a collaboration formed with a gravity research group there. Alumni of the laboratory have secured graduate fellowships and industrial positions. This award greatly contributes to the valuable expansion of research at HSU in the STEM fields.Within the major program, software developed for data acquisition and analysis will be transferable to educational opportunities in the upper division classroom. This award also allows undergraduates to participate in valuable dissemination efforts through presentations at national and regional conferences as well as publication of research results. Finally, tests of gravity are of great interest to research in diverse fields ranging from astrophysics and cosmology to particle physics and precision measurement science.