Gravitation and Cosmology
Early Universe, Cosmology, and Strings (EUCOS)
Dr. Gerald Cleaver Dr. Qin 'Tim' Sheng Dr. Klaus Kirsten
The Early Universe Cosmology and Strings Group conducts research in a variety of gravitational physics, cosmology and high energy astrophysics areas. Superstring theory is presently the only known framework providing a consistent theory of quantum gravity, allowing it to probe the earliest moments of the universe. In this sense, superstring theory may be thought of as a window to the Creation itself. Members of the EUCOS group are currently examining the construction of phenomenologically realistic superstring models, their dual models, and M-theory embeddings. Such models should yield as their low energy effective field theory either the Standard Model or the Minimal Supersymmetric Standard Model.
Additionally, the 'second string revolution' has opened up numerous new directions in string/M-theory research, many of which are cosmological in nature. Cosmology and quantum gravity are only two of the exciting areas also being investigated within EUCOS. Many aspects of gravitation and quantum cosmology, including braneworld scenarios and brane cosmology, are being examined in coordination with the GCAP group, using tools from general relativity, superstring theory and M-Theory.
Gravity, Cosmology, and Astroparticle Physics (GCAP)
Gravity, Cosmology and Astroparticle Physics Division (GCAP) conducts research in classical and quantum theories of gravity, and their applications to astrophysics and cosmology. Currently research topics include gravitational wave astronomy, black hole physics, quantum cosmology and the very early universe, and the nature and origins of dark matter and dark energy.
One of the remarkable discoveries in the history of physics is the gravitational waves, emitted during the coalescences of two compact astrophysical objects, such as black holes and neutron stars, which marks the beginning of a new era – the GW astronomy, and opens an unprecedented new window onto the cosmos. "The possibilities for discovery are as rich and boundless as they have been with light-based astronomy."Another landmark in the development of modern cosmology is the discovery that currently our universe is in an accelerating expansion phase. In Einstein's theory of general relativity, to account for such an expansion, a new component to the matter fields of the universe with a large negative pressure is needed, the so-called dark energy. Recent astronomical observations indicate that our universe is flat and currently consists of approximately 68% dark energy, 27% dark matter, and 5% baryon matter and radiation.
Group Faculty Members
Dr. Anzhong Wang (head, Physics) Dr. Klaus Kirsten (Math) Dr. Qin 'Tim' Sheng (Math) Dr. Yumei Wu (Physics)
Group Graduate Students
Jared R Fier Wen-Cong Gan Bowen Li Chao Zhang Xiang Zhao
CASPER Adjunct Professors
Ronggen Cai (ITP, Beijing, China) Yungui Gong (HZUST, Wuhan, China) JianXin Lu (USTC, Hefei, China) N.O. Santos (UPMC Universite Paris 06, France)
Areas of Interest
Over the last couple of years, GCAP researchers have focused mainly on two related areas. The first deals with the gravitational wave astronomy. A gravitational wave can be emitted by compact astrophysical objects, such as black holes and neutron stars. It can be also produced in the very early Universe, due to quantum fluctuations of space and time. The latter is often referred to as primordial gravitational waves. All the gravitational waves observed so far (August 3, 2020) were produced during the coalescences of two black holes, two neutron stars, or one black hole and one neutron star, and no primordial gravitational waves have been observed, yet. GCAP has been working in this field in the last couple of years, in collaboration with several international groups, including Prof. S. Mukoyama from Yukawa Institute for Theoretical Physics, Kyoto, Prof. Remo Ruffini, the Director of the International Centre for Relativistic Astrophysics Network (ICRANet), and the President of the International Centre for Relativistic Astrophysics (ICRA), Rome, Prof. W. Zhao from USTC, Hefei, and Profs. Q. Wu and T. Zhu, from ZJUT, Hangzhou. Their main focuses currently are on the tests of theories of gravity by observations of gravitational waves from both astrophysical compact objects and the very early Universe. These include Einstein’s general relativity, Einstein-aether theory and scalar-tensor gravity.
Another area is quantum gravity and its effects in the very early Universe and black holes, and their possible observations by current and forth-coming experiments. In particular, in the framework of Loop Quantum Cosmology (LQC), the big bang singularity is generically replaced by a non-singular quantum bounce, due to pure quantum geometric effects, from which the initial value problem of the inflationary universe may be resolved, and the evolution of the Universe can be determined from the unambiguous conditions. In addition, when applying similar ideas to the internals of black holes, the curvature singularities can be also resolved, and replaced also by a quantum bounce, although in the latter the nature of the bounce is not as clear as that in LQC. Research in this direction has involved the GCAP director, Dr. Anzhong Wang, EUCOS director Dr. Gerald Cleaver, mathematics faculty Drs. Klaus Kirsten and Tim Sheng, and their postdocs and graduate students. It is also closely involved with several national and international collaborators, Drs. Q. Wu and T. Zhu from ZJUT and Dr. Bao-Fei Li from LSU. Recently, there have been various proposals to derive quantum cosmology and black holes directly from loop quantum gravity, and found some modifications to the standard LQC model and loop quantum black holes. Lately, in collaborations with several experts of the field, including Prof. G.A. Mena Marrugan from IEM-CSIC, Spain, Prof. P. Singh from LSU, and Prof. N.O. Santos from UPMC Universite Paris 06, France, GCAP group members have been working on these modified LQC models, as well as loop quantum black holes.