AbstractConformal scaling invariance should play an important role for understanding the origin and evolution of universe. During inflation period, it appears to be an approximate symmetry, but how it is broken remains uncertain. The appealing α-attractor inflation implements the spontaneous breaking of conformal symmetry and a mysterious SO(1,1) global symmetry. To better understand the SO(1,1) symmetry, here we present a systematic treatment of the inflation models with local conformal symmetry in a more general formalism. We find SO(2) is the other possible symmetry in the presence of Weyl gauge field. We also obtain all the analytic solutions that relate the inflation fields between Jordan frame and Einstein frame. We illustrate a class of inflation models with the approximate SO(2) symmetry and trigonometric potential, and find that it can fit the current observations and will be probed by future CMB experiments. DOI: 10.1088/1475-7516/2020/03/067https://arxiv.org/pdf/1912.07610v2.pdf
AbstractThe ultra-slow-roll (USR) inflationary models predict large-amplitude scalar perturbations at small scales which can lead to the primordial black hole production and scalar-induced gravitational waves. In general scalar perturbations in the USR models can only be obtained using numerical method because the usual slow-roll approximation breaks. In this work, we propose an analytical approach to estimate the scalar spectrum which is consistent with the numerical result. We find that the USR inflationary models predict a peak with power-law slopes in the scalar spectrum and energy spectrum of gravitational waves, and we derive the expression of the spectral indexes in terms of the inflationary potential. In turn, the inflationary potential near the USR regime can be reconstructed from the negative spectral index of the gravitational wave energy spectrum.DOI: 10.1103/PhysRevD.101.083535https://arxiv.org/pdf/2003.02075.pdf
AbstractMotivated by the Weyl scaling gauge symmetry, we present a theoretical framework to explain cosmic inflation and dark matter simultaneously. This symmetry has been resurrected in recent attempts to formulate the gauge theory of gravity. We show the inspired inflation model is well consistent with current observations and will be probed further by future experiments. Furthermore, we clarify and prove the stability of Weyl gauge boson in the general theory with multiple scalars. We show the massive Weyl gauge boson can be a dark matter candidate and give the correct relic abundance.DOI: 10.1016/j.physletb.2020.135320https://arxiv.org/pdf/1904.04493.pdf
AbstractWe find the exchange symmetry between left and right handed top quark in composite Higgs model with partial compositeness is efficient to soften the Higgs potential and reduce fine tuning. This symmetry can keep the Higgs potential in top sector invariant under trigonometric parity sin(h/f)↔cos(h/f). Thus the Higgs quadratic divergences can be canceled entirely, resulting in a UV insensitive Higgs potential. We explicitly construct the minimal left-right symmetric model based on coset space SO(6)/SO(5), which is locally isomorphic to SU(4)/Sp(4) and thus has well defined fermionic UV completion. This UV completion can automatically keep Higgs potential in the gauge sector finite even the gauge sector breaks this discrete symmetry. We find that the vector mesons can be very heavy, while the colored top partners are relatively light (>1. 5TeV) to obtain a light Higgs. DOI:10.1103/PhysRevD.101.035032https://journals.aps.org/prd/pdf/10.1103/PhysRevD.101.035032
AbstractWith high spatial resolution, polarimetric imaging of a supermassive black hole, like M87* or Sgr A*, by the Event Horizon Telescope can be used to probe the existence of ultralight bosonic particles, such as axions. Such particles can accumulate around a rotating black hole through the superradiance mechanism, forming an axion cloud. When linearly polarized photons are emitted from an accretion disk near the horizon, their position angles oscillate due to the birefringent effect when traveling through the axion background. In particular, the observations of supermassive black holes M87*(Sgr A*) can probe the dimensionless axion-photon coupling c = 2πgaγfa for axions with mass around O(10−20) eV (O(10−17) eV) and decay constant fa < O(1016) GeV, which is complimentary to other axion measurements.DOI:10.1103/physrevlett.124.061102https://arxiv.org/pdf/1905.02213.pdf
AbstractBoth LISA and Taiji, planned space-based gravitational-wave detectors in orbit around the Sun, are expected to launch in 2030-2035. Assuming a one-year overlap, we explore a potential LISATaiji network to fast and accurately localize the gravitational-wave sources.DOI: 10.1038/s41550-019-1008-4https://www.nature.com/articles/s41550-019-1008-4Nature Astronomy（2020）
AbstractWe derive the generalized partial wave expansion for M → N scattering amplitude in terms of spinor helicity variables. The basis amplitudes of the expansion with definite angular momentum j consist of the Poincare Clebsch-Gordan coefficients, while j constrains the UV physics that could generate the corresponding operators at tree level. Moreover, we obtain a series of selection rules that restrict the anomalous dimension matrix of effective operators and the way how effective operators contribute to some 2 → N amplitudes at the loop level.https://arxiv.org/pdf/2001.04481.pdf
AbstractOrbital angular momentum (OAM) of light represents a fundamental optical freedom that can be exploited to manipulate quantum state of atoms. In particular, it can be used to realize spin-orbital-angular-momentum (SOAM) coupling in cold atoms by inducing an atomic Raman transition using two laser beams with differing OAM. Rich quantum phases are predicted to exist in many-body systems with SOAM coupling. Their observations in laboratory, however, are often hampered by the limited control of the system parameters. In this work we report, for the first time, the experimental observation of the ground-state quantum phase diagram of the SOAM coupled Bose-Einstein condensate (BEC). The discontinuous variation of the spin polarization as well as the vorticity of the atomic wave function across the phase boundaries provides clear evidence of first-order phase transitions. Our results open up a new way to the study of phase transitions and exotic quantum phases in quantum gases.DOI: 10.1103/physrevlett.122.110402 https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.122.110402
Abstract Practically all solar phenomena are more or less relative to the solar magnetic field. It produces relatively stable structures like sunspots or prominences and is responsible for spectacular dynamic phenomena like flares or coronal mass ejections. However, the generation, amplification and destruction of magnetic fields remain poorly understood. The knowledge of its magnitude and direction is crucial for interpreting measurements of other parameters, and it can be measured usually by a polarimetry at some special spectral lines, which should be sensitive to the Zeeman effect. To answer what physical mechanisms are responsible for heating the corona, what causes variations of radiative output in the Sun, and what mechanisms trigger flares and coronal mass ejections and so on, many large aperture solar telescope have been developed (such as VTT, GREGOR, NST) or have being developed (such as DKIST, EST), and the Stokes polarimetry is their most important observational device for determining the magnetic field. The Chinese large solar telescope (CLST) with a 1.8-m aperture is a classic Gregorian configuration telescope with an alt-azimuth mount. It will be the second largest solar telescope in the world for a long time. And it is the main task for the Chinese large solar telescope (CLST) to measure the solar polarization with a high accuracy and sensitivity. However, as a classic Gregorian configuration telescope with an alt-azimuth mount, the telescope system itself will introduce instrumental polarization. And it also will change constantly with the rotating of the telescope. Therefore a calibration unit which produces light of known polarization states is necessary to measure the Muller matrix of the system and apply the correction numerically on the measured Stokes vector.DOI: 10.12086/oee.2018.180058http://www.oejournal.org/J/OEE/Article/Details/A181101000003/CNSupported by National Natural Science Foundation of China (11178004, 11727805)
AbstractAn emergent global symmetry of the composite sector (called maximal symmetry) can soften the ultraviolet behavior of the Higgs potential and also significantly modify its structure. We explain the conditions for the emergence of maximal symmetry as well as its main consequences. We present two simple implementations and generalize both to N-site as well as full warped extra dimensional models. The gauge symmetry of these models enforces the emergence of maximal symmetry. The corresponding Higgs potentials have unique properties: one case minimizes the tuning while the other allows heavy top partners evading direct LHC bounds.DOI:10.1103/PhysRevLett.124.241801https://arxiv.org/pdf/1810.07704.pdf
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