Zhong'an Online Zhong'an News Client News Reporter learned from the University of Science and Technology of China on December 16 that professor Cai Yifu of the University of Science and Technology of China led an international cooperation team to discover the nonlinear theoretical phenomenon of primordial gravitational wave resonance when the infant universe is in the "desert" energy zone of high-energy physics. Through this process, the primordial gravitational wave signal can be amplified by resonance by 4 to 6 orders of magnitude or even greater, so that it can be detected by the primordial gravitational wave detector, which can be used to verify some theoretical models of the origin of the universe that are "untouchable" by traditional physics. This new result can provide an important scientific goal for the construction of the original gravitational wave detection experiment that is popular in the world, and also open a window for the search for high-energy new physics beyond the Standard Model of particle physics. The results were published in the internationally renowned academic journal Physical Review Letters under the title "Beating the Lyth bound by parametric resonance during inflation".
If the present universe is likened to a growing child, then in the infancy of the universe, all matter and dark matter now existed in the form of very small elementary particles. The "baby universe" is extremely hot, far exceeding the highest temperature (energy scale) that can be reached in today's high-energy physics experiments. The physics of this period is called the new physics of the high-energy zone, because beyond the current ability to explore, it is called the "desert" area of high-energy physics.
At present, the main scientific and technological means to explore the origin of the universe is to search for ripples in space-time from the creation of the universe, that is, primordial gravitational waves. It is like a phonograph that faithfully records what happened in the universe in ancient times. However, the magnitude of these space-time fluctuations is directly determined by the cosmic energy scales of infancy. Therefore, the ability to capture primordial gravitational waves has almost become the only key clue to whether humans will still have a chance to get out of the "desert" of the infant universe and find new physics in the high-energy region beyond the Standard Model of particle physics. Strictly speaking, gravitational wave detection is only one of many scientific and technological means to find new physics beyond the Standard Model of particle physics, as well as traditional collider science, high-energy cosmic rays, etc.; in the gravitational wave detection target, in addition to primordial gravitational waves, there are phase transition gravitational waves, primordial black hole induced gravitational waves, etc. But these technical means are either far from the "desert" energy region of high-energy physics, or there is still uncertainty in the physical theory behind them. Primordial gravitational waves, on the other hand, must exist as long as the thermo-big bang cosmology is established. Therefore, the scientific exploration of it has almost become the only key clue for human beings to get out of the "desert" energy zone of the infant universe and find new physics.
The "inflationary universe" is a representative hypothesis of the origin of the universe and the new physics of the high-energy region, which holds that the universe has been sharply enlarged by about 10^80 times in the instant after the creation of the Big Bang. The cosmic microwave background radiation sky map partially verifies the theory. But primordial gravitational waves, another important prophecy of inflationary theory, have not been captured for a long time. Primordial gravitational waves have become the focus of many cosmological experiments at home and abroad. Once humans have successfully captured primordial gravitational waves, whether the universe has had a very early inflationary process can be tested conclusively, and new physical energy scales in the high-energy region can also be accurately determined. But if inflation happens to occur in the high-energy physical "desert" energy region of the infant universe (higher than the current highest energy scale that humans can reach, that is, the collider experimental energy scale, but far below the theoretical energy scale of the interaction of the great unity), the corresponding primordial gravitational wave signal amplitude will be very small, almost undetectable by cosmological detection technology. The traditional academic view therefore holds that searching for primordial gravitational waves and their associated new physics in this energy region is an "impossible task."
In this study, Cai's team introduced a heavy field with parametric resonance evolution behavior, which is nonlinearly coupled with the primordial gravitational wave, thereby providing an energy source for the resonant gain of the primordial gravitational wave. And the special kinetic properties of the evolution of the inflationary background (technical term, slow-roll inflation) allow for virtually no interference between this heavy field and the traditional primordial material perturbation, thus ensuring that the inflationary theory fits perfectly with current cosmological observations.
By constructing a concrete model example, this study accurately demonstrates that even if the infant universe undergoes a process of inflation in the "desert" energy region beyond the Standard Model of particle physics, it can produce proto-gravitational waves large enough to theoretically show that the "desert" of high-energy physics may also have a vibrant new physical "oasis".
Figure 1: In the physical desert of the high-energy zone, there is a small new physical oasis, amplified by the resonance gain mechanism to the observable range, detected by the primordial gravitational wave telescope. Image source: European Space Agency/Planck Cooperation Group
According to the pre-analysis of this study, this new theoretical origin mechanism that generates primordial gravitational waves through nonlinear resonance processes is expected to be tested in the near future cosmic microwave background radiation experiments, such as the international LiteBird Space Telescope and the Chinese Ali primordial gravitational wave experiment.
Figure 2: Left: Amplitude gain of parametric resonance resonant resonant field (black line) and comparison with traditional primordial matter perturbation (red line); Right: Theoretical prediction signal (black line, red line) given by the newly proposed primordial gravitational wave resonance generation mechanism compared with the detection capability of the International LiteBird Space Telescope (green line).
This research has been funded by the Ministry of Science and Technology National Key R&D Program "Gravitational Wave Detection" Key Project, the National Natural Science Foundation of China Emergency Management Project, the International (Regional) Cooperation and Exchange Project, the Ministry of Education's Central University Basic Scientific Research Project, the State Scholarship Council Innovative Talents International Cooperation Training Project, the Chinese Academy of Sciences In the Field of Basic Research Outstanding Youth Team, and the University of Science and Technology of China International Development Fund. (Reporter Wang Qiao)