The intersection of particle physics, astrophysics, and cosmology is an exciting and data-driven field, where a combination of imaginative basic theory and observations has revolutionized our understanding of the Universe. The PI?s research focuses on several areas where the potential for new fundamental discoveries is particularly high: Dark Matter, Ultra-High Energy Cosmic Rays, and Galactic and Cosmic Magnetic Fields. Although Dark Matter (DM) is conventionally considered to be an as-yet-undiscovered particle arising in some extension of standard particle physics, instead, DM may be a manifestation of an entirely new world ? possibly as complex as our own ? whose properties we can only infer through gravity. For instance, if our world is a brane in a higher dimensional space, there could be other branes nearby in some new dimension, whose presence we could only discover through their gravitational effects. Although still inconclusive, evidence has been mounting that Dark Matter may have a long range interaction with itself, which the PI has recently shown would be a smoking gun for a disconnected Dark Sector. The PI, her collaborators and her students will extend simulations of cosmological structure formation and of the tidal stripping of dwarf galaxies bound to the Milky Way, to include the possibility of new forces in the Dark Sector. Detailed comparison with these and other observations will either show the presence of a new force and allow some properties of the Dark Sector to be inferred, or will put stringent limits on Dark Sector interactions. Related questions that will be investigated are: Do dark matter and dark energy interact with each other? Why is the abundance of dark matter about equal to that of ordinary matter? Another important topic of research is the highest energy particles in Nature ? ultrahigh energy cosmic rays (UHECRs). The aim is to pin down what they are, and how and where in the Universe they are accelerated or created. The third main effort is to map out the Galactic Magnetic Field with much greater accuracy than ever before, by making a combined fit of many different types of observations. The PI is involved in an international collaboration to develop state-of-the-art techniques for optimizing fits involving many parameters and hundreds of millions of measured data points. The PI intends to take the New York Schools Cosmic Particle Telescope (NYSCPT) project to the next stage of its successful partnership with NYC schools by prototyping rooftop water tank detectors and designing a full-sized The PI is involved in mentoring high school students, teacher and student participants of NYSCPT, women graduate students, postdoctoral researchers and junior faculty. She is also a founding participant of the NYU ?WINS? program to foster undergraduate women?s participation in science.
Some of the most important results from this grant are: Discovery of two examples of entire stars being shredded and consumed by a black hole. More than two decades ago, it was predicted that about once every 100,000 years in a galaxy like the Milky Way, a star will get close enough to the supermassive black hole (SMBH) at the center of the galaxy, that it will be shredded by the gravitational "tidal" force: the force of gravity on the side closer to the SMBH is so much greater than on the far side, that the star is literally torn apart. About half of the debris falls into the SMBH and disappears, and the rest becomes an extremely hot plasma orbiting the SMBH and emitting visible and ultraviolet light and x-rays for a few months. Observing such "tidal disruption events" (TDEs) has been an important goal of astrophysics, because the properties of a flare give information about the mass and spin of the SMBH, as well as the victim star and its orbit. WIth a large number of TDEs, questions can be answered about the growth of supermassive black holes and the distribution of their spins, which cannot be addressed in any other way and which are crucially important for understanding cosmology and even fundamental questions in particle physics. Up until our discovery of these two events, no one had succeeded in finding these flares in a systematic search with optical telescopes because they are much more rare than other types of flares; some candidates had been detected by chance by the GALEX satellite, but these are difficult to evaluate and interpret. The PI and a graduate student developed a powerful method to search for TDE flares in the Sloan Digital Sky Survey archive, capable of rejecting the factor-100 larger number of flares of a more common type such as Supernovae and the flares from variable quasars. We got spectra and observations with other telescopes that confirmed the SDSS-based identification of these two examples as Tidal Disruption Events. The flares are much brighter than had been predicted, which bodes well for future campaigns based on our approach, to identify large numbers of TDEs. Our discovery of two optical tidal disruption flares is important both because of what these first examples teach us about this phenomenon, and because our method demonstrates the feasibility of a future large-scale detection campaign with immediate detailed follow-up observations at many wavelengths. Other notable discoveries: The PI with one of her postdocs and other colleagues repurposed a published result from the Tevatron, to show that that the mass of the "gluino" – a hypothesized new particle predicted by the theory of Supersymmetry, the doppelganger of the gluon which inseparably binds quarks together -- must be over 300 times larger than the mass of a proton, even if the gluino is stable or very long lived; prior to our work such a stable gluino could have evaded discovery. The PI and another of her postdocs made the first reliable determination of the large-scale magnetic field of the Milky Way galaxy, by combining 40,000 data points from WMAP with a comparable number of radio observations of extragalactic sources, to fix the parameters of a general field model. This will enable WMAP and Planck (satellites measuring the Cosmic Microwave Background Radiation) to search for signals from gravitational waves created in the Big Bang with better control of their foregrounds from Galactic emission. The PI and one of her grad students studied the particle showers produced when Ultrahigh Energy Cosmic Rays hit the Earth’s atmosphere, as measured by the Pierre Auger Observatory. These extremely rare events (one per year in 10 square kilometers) give insight into particle interactions at energies far above those attainable in man-made particle accelerators such as the LHC. Existing models of particle physics do not adequately describe the showers, hinting that new processes not encountered at lower energies may come into play. We developed a method to discern the composition of the primary UHECR particles without relying on shower models. Education and Outreach: The New York Schools Cosmic Particle Telescope Project is being carried out by a group of volunteers – high school students, undergraduate and graduate students, and members of the public -- under the leadership of the PI. The ultimate goal is to outfit hundreds of NYC’s ubiquitous rooftop emergency watertanks, to create a detector to discover and study very high energy neutrinos which are created in extreme astrophysical events and travel to us across the Universe. We tested the feasibility of the concept by outfitting a demo tank on an NYU building, successfully running it year-round, and measuring the signal from single muons; this study will allow the next-stage demo to be designed.
