Conveners
Day 2: Fundamental gravity and observational tests
- Atsuhisa Ota (Chongqing University)
Day 2: Modified gravity and black holes
- Dražen Glavan (Institute of Physics of the Czech Academy of Sciences)
Day 2: Young Talent Session
- Xian Gao (Sun Yat-sen University)
This report explores the detection capabilities of multi-band gravitational wave detectors for extra polarizations beyond general relativity. In the mHz–kHz band, the extended parameterized post-Einsteinian (ppE) framework is applied to space-based (e.g., LISA, Taiji, TianQin) and ground-based (e.g., LIGO, Virgo, KAGRA, ET) detectors, showing that multi-band observations effectively break...
We discuss several aspects of tunneling in cosmology.
I will review the recently proposed GEVAG (generalized entropy and varying-G) theory. This theory gives a consistent treatment of how the field equation of gravity should be changed if the area law of horizon entropy is modified, namely that gravitational constant G is now area-dependent, the functional form of which depends on the specific modifications of the entropy. Specifically, GEVAG was...
This talk presents recent progress in the construction of scalar-tensor theories, with a focus on parity violation and multiple scalar fields. I will first review the relation between generally covariant scalar-tensor theories and spatially covariant gravity in the unitary gauge, emphasizing how this correspondence provides an efficient way to control higher-order time derivatives and avoid...
Einstein’s theory describes gravity through spacetime curvature, but more general gauge-theoretic frameworks allow spacetime to carry torsion and nonmetricity as well. I will first introduce metric-affine gravity as a framework in which curvature, torsion, and nonmetricity have distinct geometric roles, and discuss the theoretical consequences of these structures, including their relation to...
Black holes beyond General Relativity may carry non-standard charges that impact their phenomenology. I will present the scalar charge that is induced by the scalar-Gauss-Bonnet coupling and how it is affected by the presence of a nontrivial kinetic term K(X). I will discuss the corresponding kinetic screening in the asymptotically flat, static solution first. I will then turn to the case...
In this talk I will give an overview of several beyond Standard model theories predicting a large number of additional degrees of freedom. The corresponding softening in equations of state can be significant. I will show that, within these models, it is then possible to achieve a large enhancement in PBH abundance on scales relevant for PBHDM; namely, the asteroid mass and memory burden windows.
Strong nuggets with a baryon number of A=10^10-10^30 could be able to survive from the cosmic separation of the QCD phases, provided the transition from strange quark matter to strangeon matter is accounted for, thereby evading evaporation in the early Universe. Such strangeon nuggets may serve as a dark matter candidate within particle standard model. We formulate the corresponding phase...
The definition of second-order gravitational wave (GW) strain in cosmological perturbation theory is traditionally ambiguous due to its dependence on spacetime slicing. This issue is particularly critical for secondary GWs induced by primordial fluctuations. This talk introduces a gauge-invariant formalism that defines GW strain via the time-delay of electromagnetic signals exchanged between...
We utilize the $\delta N$ formalism within a parameter space formed by the $e$-folding number $N$ and its transverse subspace to explicitly account for the geometry of the final hypersurface in multi-field inflation. Applying this framework to hybrid inflation, we identify an enhancement mechanism of the curvature perturbation driven by the growing isocurvature perturbation due to the...
We construct and solve a complete system of differential equations for general tree-level inflation correlators with an arbitrary number of massive scalar exchanges and time-dependent couplings. Any massive tree correlators can be uniquely fixed by solving this system of equations with appropriate boundary conditions. We take a hybrid approach to solve this system, using the differential...
Cosmological correlators with massive loop exchanges appear frequently in cosmological collider model building as promising sources of oscillatory signals. However, their computations remain challenging. In this work, we apply the family-tree decomposition to correlators at loop level and derive rules to directly write down analytic answers for arbitrary massive loop integrands in terms of...
The particle model building of cosmological collider physics often involves boost-breaking bilinear mixing between a heavy particle and the nearly massless inflaton mode. In cosmological correlators, such a mixing is obtained by taking a folded limit of a generic tree graph, which is a special case of degenerate kinematics. In this work, we continue our exploration of massive inflationary...
Ultra-light primordial black holes (PBHs), formed from small-scale fluctuations, could temporarily dominate the energy density of the early universe and leave distinctive gravitational-wave (GW) signatures through their evaporation. These signals provide a novel window into the PBH mass, abundance, spatial distribution, and evaporation process. In this talk, the speaker will discuss how...
