AbstractThe existing constraints from particle colliders reveal a suspicious but nonlethal meta-stability for our current electroweak vacuum of Higgs potential in the standard model of particle physics, which is, however, disfavored in the early Universe if the inflationary Hubble scale is larger than the instability scale when Higgs quartic self-coupling runs into negative value. Alternative to previous trials of acquiring a positive effective mass-squared from Higgs quadratic couplings to Ricci scalar or inflaton field, we propose a third approach to stabilize the Higgs potential in the early Universe by regarding Higgs as chameleon coupled to inflaton alone without conflicting to the present constraints on either Higgs or chameleon.https://arxiv.org/pdf/2005.12885.pdf
AbstractWe describe the on-shell method to deriving the Renormalization Group (RG) evolution of Wilson coefficients of high dimensional operators at one loop, which is a necessary part in the on-shell construction of the Standard Model Effective Field Theory (SMEFT), and exceptionally efficient based on the amplitude basis in hand. The UV divergence is obtained by firstly calculating the coefficients of scalar bubble integrals by unitary cuts, then subtracting the IR divergence in the massless bubbles, which can be easily read from the collinear factors we obtained for the Standard Model fields. Examples of deriving the anomalous dimensions at dimension six are presented in a pedagogical manner. We also give the results of contributions from the dimension-8 H4D4 operators to the running of V+V−H2 operators, as well as the running of B+B−H2D2n from H4D2n+4 for general n.https://arxiv.org/pdf/2005.10261.pdf
AbstractWe present a complete list of the dimension 8 operator basis in the standard model effective field theory usinggroup theoretic techniques in a systematic and automated way. We adopt a new form of operators in terms of the irreducible representations of the Lorentz group, and identify the Lorentz structures as states in a SU(N) group. In this way, redundancy from equations of motion is absent and that from integration-by-part is treated using the fact that the independent Lorentz basis forms an invariant subspace of the SU(N) group. We also decompose operators into the ones with definite permutation symmetries among flavor indices to deal with subtlety from repeated fields. For the first time, we provide the explicit form of independent flavor-specified operators in a systematic way. Our algorithm can be easily applied to higher dimensional standard model effective field theory and other effective field theories, making these studies more approachable.https://arxiv.org/pdf/2005.00008.pdf
AbstractThe binary black holes (BBHs) formed near the supermassive black holes (SMBHs) in the galacticnuclei would undergo eccentricity excitation due to the gravitational perturbations from the SMBH and therefore merger more efficiently. In this paper, we study the coupling of the three body 1st post-Newtonian (pN) effects with the spin effects from the SMBH in the hierarchical triple system.The three body 1pN effects yielding the de-Sitter precession is usually decoupled in the secular dynamics, while it couples to the spin of SMBH through the Lense-Thirring precession of the outer orbital plane. This coupling includes both the precessions of the inner orbit angular momentum and the Runge-Lenz vector around the outer orbit angular momentum in a general reference frame. Our general argument on the coupling of the three body 1pN effects in three body systems could be extended to any other situation as long as the outer orbital plane evolves.https://arxiv.org/pdf/2004.09390v1.pdf
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）