AbstractWe investigate a new mechanism to create large curvature perturbations on small scales due to parameter resonance in a single-field inflationary model with a small periodic structure upon the potential. After reentering the horizon, the amplified curvature perturbations can lead to observable primordial black holes as well as stochastic gravitational waves. The mass of primordial black holes and frequency of the induced gravitational waves depend on the model parameters. The resulted primordial black hole could constitute all dark matter or a fraction of dark matter in the universe, and corresponding stochastic gravitational waves fall in the frequency band measurable for the pulsar timing array and the space-based gravitational wave detectors.DOI: 10.1088/1475-7516/2020/06/013https://arxiv.org/pdf/1912.10437.pdf
AbstractWe review potential low-frequency gravitational-wave sources, which are expected to be detected by Taiji, a Chinese space-based gravitational-wave detector, estimate the detection rates of these gravitational-wave sources and present the parameter estimation of massive black hole binaries.DOI:10.1142/S0217751X2050075Xhttps://www.worldscientific.com/doi/abs/10.1142/S0217751X2050075XInternational Journal of Modern Physics A（2020）
AbstractInflation in the early universe can generate the nearly conformal invariant fluctuation that leads to the structures we observe at the present. The simple viable Starobinsky R2 inflation has an approximate global scale symmetry. We study the conformal symmetric Weyl R2 gravity and demonstrate its equivalence to Einstein gravity coupled with a scalar and a Weyl gauge field. The scalar field can be responsible for inflation with Starobinsky model as the attractor, potentially distinguishable from the latter by future experiments. The intrinsic Weyl gauge boson becomes massive once the Einstein frame is fixed, and constitutes as a dark matter candidate through gravitational production.https://arxiv.org/pdf/2006.02811v1.pdf
AbstractWe propose a new type of search for a pseudoscalar particle η pair produced via an off-shell Higgs, pp→h∗→ηη. The search is motivated by a composite Higgs model in which the η is extremely narrow and decays almost exclusively into Zγ in the mass range 65 GeV≲mη≲160 GeV. We devise an analysis strategy to observe the novel ZγZγ channel and estimate potential bounds on the Higgs-η coupling. The experimental sensitivity to the signatures depends on the power to identify fake photons and on the ability to predict large photon multiplicities. This search allows us to exclude large values of the compositeness scale f, being thus complementary to other typical processes.https://arxiv.org/pdf/2005.13578.pdf
AbstractTreating the gravitational force on the same footing as the electroweak and strong forces, we present a quantum field theory of gravity based on spin and scaling gauge symmetries. A biframe spacetime is initiated to describe such a quantum gravity theory. The gravifield sided on both locally flat noncoordinate spacetime and globally flat Minkowski spacetime is an essential ingredient for gauging global spin and scaling symmetries. The locally flat gravifield spacetime spanned by the gravifield is associated with a non-commutative geometry characterized by a gauge-type field strength of the gravifield. A coordinate-independent and gauge-invariant action for the quantum gravity is built in the gravifield basis. In the coordinate basis, we derive equations of motion for all quantum fields including the gravitational effect and obtain basic conservation laws for all symmetries. The equation of motion for gravifield tensor is deduced in connection directly with the total energy-momentum tensor. When the spin and scaling gauge symmetries are broken down to a background structure that possesses the global Lorentz and scaling symmetries, we obtain exact solutions by solving equations of motion for the background fields in a unitary basis. The massless graviton and massive spinon result as physical quantum degrees of freedom. The resulting Lorentzinvariant and conformally flat background gravifield spacetime is characterized by a cosmic vector with a nonzero cosmological mass scale. The evolving Universe is, in general, not isotropic in terms of conformal proper time. The conformal size of the Universe becomes singular at the cosmological horizon and turns out to be inflationary in light of cosmic proper time. A mechanism for quantum scalinon inflation is demonstrated such that it is the quantum effect that causes the breaking of global scaling symmetry and generates the inflation of the early Universe, which is ended when the evolving vacuum expectation value of the scalar potential gets a minimal. Regarding the gravifield as a Goldstone-like field that transmutes the local spin gauge symmetry into the global Lorentz symmetry with a hidden general coordinate invariance, a spacetime gauge field is constructed from the spin gauge field that becomes a hidden gauge field. The bosonic gravitational interactions are described by the Goldstone-like gravimetric field and spacetime gauge field. Two types of gravity equation result; one is as the extension to Einstein’s equation of general relativity, and the other is a new one that characterizes spinon dynamics. The Einstein theory of general relativity is considered to be an effective low-energy theory.DOI:10.1103/PhysRevD.93.024012https://arxiv.org/pdf/1506.01807.pdf
AbstractThe detection of binary black hole coalescences by LIGO/Virgo has aroused the interest in primordial black holes (PBHs), because they could be both the progenitors of these black holes and a compelling candidate of dark matter (DM). PBHs are formed soon after the enhanced scalar perturbations re-enter horizon during radiation dominated era, which would inevitably induce gravitational waves as well. Searching for such scalar induced gravitational waves (SIGWs) provides an elegant way to probe PBHs. We perform the first direct search for the signals of SIGWs accompanying the formation of PBHs in North American Nanohertz Observatory for Gravitational waves (NANOGrav) 11-year data set. No statistically significant detection has been made, and hence we place a stringent upper limit on the abundance of PBHs at 95% confidence level. In particular, less than one part in a million of the total DM mass could come from PBHs in the mass range of [2∗10-3,7∗10-1]MΘ.DOI: 10.1103/PhysRevLett.124.251101https://arxiv.org/pdf/1910.12239.pdf
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
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