Dark energy and matter interacting scenario to relieve H_(0) and S_(8) tensions

We consider a new cosmological model(calledΛCDM),in which the vacuum energy interacts with matter and radiation,and test this model using the current cosmological observations.Using the CMB+BAO+SN(CBS)dataset to constrain the model,we find that H_(0) and S_(8) tensions are relieved to 2.87σand 2.77σ,respectively.However,in this case,theΛCDM model is not favored by the data,compared withΛCDM.We find that when the H_(0) and S_(8) data are added to the data combination,the situation is significantly improved.In the CBS+H_(0) case,the model relieves the H_(0) tension to 0.47σ,and the model is favored overΛCDM.In the CBS+H_(0)+S_(8) case,we obtain a synthetically best situation,in which the H_(0) and S_(8) tensions are relieved to 0.72σand 2.11σ,respectively.In this case,the model is most favored by the data.Therefore,this cosmological model can greatly relieve the H_(0) tension and simultaneously effectively alleviate the S_(8) tension.

Taiji data challenge for exploring gravitational wave universe

The direct observation of gravitational waves(GWs)opens a new window for exploring new physics from quanta to cosmos and provides a new tool for probing the evolution of universe.GWs detection in space covers a broad spectrum ranging over more than four orders of magnitude and enables us to study rich physical and astronomical phenomena.Taiji is a proposed space-based gravitational wave(GW)detection mission that will be launched in the 2030s.Taiji will be exposed to numerous overlapping and persistent GW signals buried in the foreground and background,posing various data analysis challenges.In order to empower potential scientific discoveries,the Mock Laser Interferometer Space Antenna(LISA)data challenge and the LISA data challenge(LDC)were developed.While LDC provides a baseline framework,the first LDC needs to be updated with more realistic simulations and adjusted detector responses for Taiji’s constellation.In this paper,we review the scientific objectives and the roadmap for Taiji,as well as the technical difficulties in data analysis and the data generation strategy,and present the associated data challenges.In contrast to LDC,we utilize second-order Keplerian orbit and second-generation time delay interferometry techniques.Additionally,we employ a new model for the extreme-mass-ratio inspiral waveform and stochastic GW background spectrum,which enables us to test general relativity and measure the non-Gaussianity of curvature perturbations.Furthermore,we present a comprehensive showcase of parameter estimation using a toy dataset.This showcase not only demonstrates the scientific potential of the Taiji data challenge(TDC)but also serves to validate the effectiveness of the pipeline.As the first data challenge for Taiji,we aim to build an open ground for data analysis related to Taiji sources and sciences.More details can be found on the official website(taiji-tdc.ictp-ap.org).

Unified field theory of basic forces and elementary particles with gravitational origin of gauge symmetry in hyper-spacetime

The theory of general relativity(GR)[1,2]has successfully built a relation between the geometry of spacetime and the energymomentum tensor of matter.Einstein has extensively quested for potential unified models of electromagnetism and gravity at a classical unified field theory and spent the last two decades of his

Maximal symmetry and mass generation of Dirac fermions and gravitational gauge field theory in six-dimensional spacetime

The relativistic Dirac equation in four-dimensional spacetime reveals a coherent relation between the dimensions of spacetime and the degrees of freedom of fermionic spinors. A massless Dirac fermion generates new symmetries corresponding to chirality spin and charge spin as well as conformal scaling transformations. With the introduction of intrinsic W-parity, a massless Dirac fermion can be treated as a Majorana-type or Weyl-type spinor in a six-dimensional spacetime that reflects the intrinsic quantum numbers of chirality spin. A generalized Dirac equation is obtained in the six-dimensional spacetime with a maximal symmetry. Based on the framework of gravitational quantum field theory proposed in Ref. [1] with the postulate of gauge invariance and coordinate independence, we arrive at a maximally symmetric gravitational gauge field theory for the massless Dirac fermion in six-dimensional spacetime. Such a theory is governed by the local spin gauge symmetry SP（1,5） and the global Poincar′e symmetry P（1,5）= SO（1,5） P^1,5 as well as the charge spin gauge symmetry SU（2）. The theory leads to the prediction of doubly electrically charged bosons. A scalar field and conformal scaling gauge field are introduced to maintain both global and local conformal scaling symmetries. A generalized gravitational Dirac equation for the massless Dirac fermion is derived in the six-dimensional spacetime. The equations of motion for gauge fields are obtained with conserved currents in the presence of gravitational effects. The dynamics of the gauge-type gravifield as a Goldstone-like boson is shown to be governed by a conserved energy-momentum tensor, and its symmetric part provides a generalized Einstein equation of gravity. An alternative geometrical symmetry breaking mechanism for the mass generation of Dirac fermions is demonstrated.

Gravity and Spin Forces in Gravitational Quantum Field Theory

In the new framework of gravitational quantum field theory(GQFT) with spin and scaling gauge invariance developed in Phys. Rev. D 93(2016) 024012-1, we make a perturbative expansion for the full action in a background field which accounts for the early inflationary universe. We decompose the bicovariant vector fields of gravifield and spin gauge field with Lorentz and spin symmetries SO(1,3) and SP(1,3) in biframe spacetime into SO(3) representations for deriving the propagators of the basic quantum fields and extract their interaction terms. The leading order Feynman rules are presented. A tree-level 2 to 2 scattering amplitude of the Dirac fermions, through a gravifield and a spin gauge field, is calculated and compared to the Born approximation of the potential. It is shown that the Newton's gravitational law in the early universe is modified due to the background field. The spin dependence of the gravitational potential is demonstrated.

Equation of state and chiral transition in soft-wall AdS/QCD with a more realistic gravitational background

We construct an improved soft-wall AdS/QCD model with a cubic coupling term of the dilaton and the bulk scalar field.The background fields in this model are solved by the Einstein-dilaton system with a nontrivial dilaton potential,which has been shown to reproduce the equation of state from the lattice QCD with two flavors.The chiral transition behaviors are investigated in the improved soft-wall AdS/QCD model with the solved gravitational background,and the crossover transition can be realized.Our study provides the possibility to address the deconfining and chiral phase transitions simultaneously in the bottom-up holographic framework.

Chiral effective Lagrangian for excited heavy-light mesons from QCD

We derive the chiral effective Lagrangian for excited heavy-light mesons from QCD under proper approximations.We focus on the chiral partners with j_(l)^(P)=3+/2 and j_(l)^(P)=3-/2 which amounts to(1^(+),2^(+))and(1^(-),2^(-))states respectively.The low energy constants including the masses of the chiral partners are calculated.The calculated spectrum for the excited mesons are found roughly consistent with experimental data.In addition,our results indicate that quantum numbers of B_(J)(5970)can be identified with 1^(-)or 2^(-).

Probing dark matter spikes via gravitational waves of extreme-mass-ratio inspirals

The exact properties of dark matter remain largely unknown despite the accumulating evidence. If dark matter is composed of weakly interacting massive particles, it would be accreted by the black hole in the galactic center and form a dense, cuspy spike.Dynamical friction from this spike may have observable effects in a binary system. We consider extreme-mass-ratio inspiral(EMRI) binaries comprising massive black holes harbored in dark matter spikes and stellar mass objects in elliptic orbits. We find that the gravitational-wave waveforms in the frequency domain can be substantially modified. In particular, we show that dark matter can suppress the characteristic strain of a gravitational wave at low frequency but enhance it at a higher domain.These effects are more dramatic as the dark matter density increases. The results indicate that the signal-to-noise ratio of EMRIs can be strongly reduced near 10^(-3)-0.3 Hz but enhanced near 1.0 Hz with a higher sensitivity, which can be probed via the future space-borne gravitational-wave(GW) detectors, LISA and TAIJI. The findings will have important impacts on the detection and parameter inference of EMRIs.

Topology change and emergent scale symmetry in compact star matter via gravitational wave detection

Topological structure has been extensively studied and confirmed in highly correlated condensed matter physics. We explore the gravitational waves emitted from binary neutron star mergers using the pseudoconformal model for dense nuclear matter for compact stars. This model considers the topology change and the possible emergent scale symmetry and satisfies all the constraints from astrophysics. We find that the location of the topology change affects gravitational waves dramatically owing to its effect on the equation of state. In addition, the effect of this location on the waveforms of the gravitational waves is within the ability of the on-going and up-coming facilities for detecting gravitational waves, thus suggesting a possible way to measure the topology structure in nuclear physics.