### Conveners

#### Gravitational Waves as Probes for New Physics

- Yungui Gong (Huazhong University of Science and Technology)

#### Gravitational Waves as Probes for New Physics

- Sugumi Kanno

#### Gravitational Waves as Probes for New Physics

- Yungui Gong (Huazhong University of Science and Technology)

#### Gravitational Waves as Probes for New Physics

- Anzhong Wang (Baylor University)

#### Gravitational Waves as Probes for New Physics

- Sugumi Kanno

#### Gravitational Waves as Probes for New Physics

- Yungui Gong (Huazhong University of Science and Technology)

#### Gravitational Waves as Probes for New Physics

- Sugumi Kanno

#### Gravitational Waves as Probes for New Physics

- Yungui Gong (Huazhong University of Science and Technology)

#### Gravitational Waves as Probes for New Physics

- Anzhong Wang (Baylor University)

#### Gravitational Waves as Probes for New Physics

- Yungui Gong (Huazhong University of Science and Technology)

#### Gravitational Waves as Probes for New Physics

- Yungui Gong (Huazhong University of Science and Technology)

#### Gravitational Waves as Probes for New Physics

- Anzhong Wang (Baylor University)

Primordial gravitational waves (GWs) can be generated during different eras of early cosmic evolution, including inflation, cosmic phase transition, reheating/preheating, and so on. In this talk, I will first introduce the amplified GWs through parametric resonance during inflation in the Cherns-Simons gravity. Then, I will introduce the scalar induced GWs accompanied with the production of...

Primordial black holes (PBHs) may form when the high peaks of the primordial density perturbation re-enter the Hubble horizon, while at the same time gravitational waves induced by the density perturbation at second order are generated. Currently observational constraints make it possible for asteroid-mass PBHs to be all dark matter, whose concomitant induced GWs are in the millihertz band. I...

I will report the current progress in our works on the detection of primordial black holes (PBHs) with gravitational waves, including the transients and the stochastic background of gravitational waves (SGWB). The observations of gravitational waves by LIGO open a new window to probe the PBHs, which could be a viable candidate of cold dark matter. We find that the scenario of PBHs can explain...

The properties of primordial curvature perturbations on small scales are still unknown while those on large scales have been well probed by the observations of the cosmic microwave background anisotropies and the large scale structure. We propose the reconstruction method of primordial curvature perturbations on small scales through the merger rate of binary primordial black holes, which could...

The axion objects such as axion mini-clusters and axion clouds around spinning black holes induce parametric resonances of electromagnetic waves through the axion-photon interaction. In particular, it has been known that the resonances from the axion with the mass around mueV may explain the observed fast radio bursts (FRBs). Here we argue that similar bursts of high frequency gravitational...

Pulsar timing arrays record the arrival time of radio pulses from dozens of millisecond pulsars. The pulsars of different sky locations construct a network that is sensitive to gravitational waves and dark matter signals. There are three Pulsar timing arrays in the world, PPTA, EPTA and NANOGrav, that are actively gathering pulsar timing data with very high precision. In this talk, we use the...

Binary extreme-mass-ratio inspiral (b-EMRIs) consists of a stellar-mass binary black hole orbiting around a supermassive massive black hole. Such a three-body system emits simultaneously low-frequency (milli-Hertz) gravitational waves and high-frequency (hundred Hertz) ones. Therefore, it is ideal for testing the dispersion of gravitational waves. In this talk, I will show how such systems...

After the discovery of Higgs boson and gravitational wave (GW), the phase transition GW becomes a new and realistic approach to explore new physics and the fundamental physics. However, current predictions on the phase transition GW have large uncertainties from energy budget, bubble

wall velocity and so on. We study how to obtain more precise phase transitional GW

In the era of gravitational wave astronomy/cosmology, it is important not only to improve the sensitivity of existing detectors but also to extend detectable frequency range with novel methods. We show that gravitational waves can induce resonant spin precessions of electrons (magnon) in the presence of an external magnetic field. This phenomenon, we call it graviton-magnon resonance, enables...

After motivating gravity and cosmology beyond general relativity, I will review some theories and their phenomenologies, inclucing gravitational wave physics.

Lorentz symmetry is the cornerstone of modern physics, and is consistent with all experiments carried out so far. However, due to various motivations, gravitational theories with Lorentz symmetry breaking have been proposed, and one of the examples is the Horava-Lifshitz theory, motivated by the quantization of gravity. Another example is the Einstein-aether (æ-) theory, which is a...

The orbital period loss of Hulse-Taylor binary system was the first indirect evidence of gravitational wave (GW) which confirms Einstein's general theory of relativity to a very good extent. However the uncertainty in the measurement of GW from observation and GR prediction allows us to probe physics beyond the standard picture. In this talk I will discuss about probing beyond standard model...

A fast-spinning axion can dominate the Universe at early times and generates the so-called kination era. The presence of kination imprints a smoking-gun spectral enhancement in the primordial gravitational-wave (GW) background. Current and future-planned GW observatories could constrain particle theories that generate the kination phase. Surprisingly, the viable parameter space allows for a...

There are strong interests in considering ultra-light scalar fields (especially axion) around a rapidly rotating black hole because of the possibility of observing gravitational waves from axion condensate (axion cloud) around black holes. Motivated by this consideration, we propose a new method to study the dynamics of an ultra-light scalar field with self-interaction around a rapidly...

We show that photon spheres of supermassive black holes generate high-frequency stochastic gravitational waves through

the photon-graviton conversion.

Remarkably, the frequency is universally determined as $m_e\sqrt{m_e /m_p} \simeq 10^{20} \text{Hz}$ in terms of the proton mass $m_p$ and the electron mass $m_e$.

It turns out that the density parameter of the stochastic gravitational...

I will argue that the slope of the spectrum of

gravitational waves may provide us evidence of

superstring effects in early universe cosmology. Both

String Gas Cosmology and the S-Brane Mediated Ekpyrotic

scenario predict a blue tilt of the tensor spectrum.

We discuss the footprint of evaporation of primordial black holes (PBHs) on stochastic gravitational waves(GWs) induced by scalar perturbations. We consider the case where PBHs once dominated the Universe but eventually evaporated before the big bang nucleosynthesis. The reheating through the PBH evaporation could end with a sudden change in the equation of state of the Universe compared to...

I will discuss the current status of the production of stochastic GW backgrounds by cosmological phase transitions. Main focus will be the differences between fully hydrodynamic simulations and the recently presented hybrid approach. I will also touch on recent results on the energy budget of the phase transition and the LISA sensitivity forecasts using likelihood sampling.

Based on arXiv:...

We will discuss energy budget of first order phase transitions and identify models capable of supporting extreme supercooling necessary to feature bubble collisions as the main source of gravitational waves. We will also review the new semi-analytical calculation of the spectrum appropriate in such strong transitions.

Over the next few decades, we will have an exciting opportunity to detect GWs from the early Universe with space interferometers. In this talk, we first propose an efficient numerical scheme to calculate GWs from sound waves in first-order phase transitions, which reveals more detailed structure of the spectrum. Based on this simulation, we next discuss the possibility of the enhancement of...

I discuss to what extend LISA can observe features of gravitational wave spectra originating from cosmological first-order phase transitions. I focus on spectra which are of the form of double-broken power laws. These spectra are predicted by hydrodynamic simulations and also analytical models such as the sound shell model. I argue that the ratio of the two break frequencies is an interesting...

We study gravity wave production and baryogenesis at the electroweak phase transition in a real singlet scalar extension of the Standard Model, including vectorlike top partners, to generate the CP violation needed for electroweak baryogenesis (EWBG). The singlet makes the phase transition strongly first order through its coupling to the Higgs boson, and it spontaneously breaks CP invariance...

In order to solve the hierarchy problem, the relaxion must remain trapped in the correct minimum, even if the electroweak symmetry is restored after reheating. In this scenario, the relaxion starts rolling again until the back-reaction potential, with its set of local minima, reappears. Depending on the time of barrier-reappearance, Hubble friction alone may be insufficient to re-trap the...

The recent gravitational wave observations of the collision of black holes and neutron stars have allowed us to pierce into the extreme gravity regime, where gravity is simultaneously unfathomably large and wildly dynamical. These waves encode a trove of information about physics that is prime for the taking, including potential revelations about the validity of Einstein's theory and possible...

Gravitational waves produced by astrophysical sources and propagation through cosmic distances in inhomogeneous universe

In this talk, we shall present our recent studies of gravitational waves (GWs) first produced by remote compact astrophysical sources and then propagating in our inhomogeneous universe through cosmic distances, before arriving at detectors. To describe such GWs...

Gravitational wave observations provide a plethora of opportunities to explore questions in fundamental physics and physics beyond the standard model. Multimessenger observation of of gravitational waves and electromagnetic radiation from distant sources can be used to test modified theories of gravity, measure cosmological parameters, ascertain the nature of dark matter and dark energy....

We derive an effective equation-of-motion for an expanding bubble wall in the thermal plasma with a general form of the thermal friction. The efficiency factor for gravitational waves productions from colliding bubble walls is obtained with a special interest for the strong first-order phase transition.

Extra dimensions are expected to solve some long-standing problems in the Standard Model of particle physics. Searching for their traces in our Universe helps to promote our understanding on the physics. Taking advantage of the source property of gravitational waves (GWs), extra dimensions might leave observable effects on GWs. Thus the observation of GWs becomes a new way to probe and study...

We consider Kaluza-Klein (KK) resonances with masses $m_{\rm KK}$ at the multi-TeV scale, out of reach of LHC. The backreaction of the radion field on the gravitational metric is taken into account by using the superpotential formalism. The confinement/deconfinement first order phase transition leads to a gravitational wave stochastic background which mainly depends on the scale $m_{\rm KK}$...

We argue that black hole area quantization, in the form predicted by Bekenstein and Mukhanov, could leave observable imprints in the gravitational-wave signal of a binary black hole merger by affecting the absorption properties of the black holes. These imprints include gravitational-wave echoes after the ringdown stage, and suppressed tidal heating during the inspiral phase. This...

One of the most ubiquitous features of quantum theories is the existence of zero-point fluctuations in their ground states. For massive quantum fields, these fluctuations decouple from infrared observables in ordinary field theories. However, there is no "decoupling theorem" in Quantum Gravity, and we recently showed that the vacuum stress fluctuations of massive quantum fields source a red...

GW190521 in a class of its own is a different signal, being the most massive BBH event observed to date. The exceptionally dominant ringdown of this event and its large mass makes it a plausible candidate to search for GW echoes. In this letter we perform an unprecedented search in two different platforms, satisfying a physical template (matched filtering and MCMC with PyCBC) and model...

We study the cosmological propagation of gravitational waves (GW) beyond general relativity (GR) across homogeneous and isotropic backgrounds. We consider scenarios in which GWs interact with an additional tensor field and use a parametrized phenomenological approach that generically describes their coupled equations of motion. We analyze four distinct classes of derivative and...

The symmetry breaking of grand unified gauge groups in the early universe often leaves behind relic topological defects such as cosmic strings, domain walls, or monopoles. For some symmetry breaking chains that produce domain walls, the accompanied presence of strings can lead to the destruction of the domain wall network, alleviating tension with present-day cosmology and to unique...

In the presence of an ultralight bosonic field, spinning black holes are unstable to superradiance. The rotational energy of the black hole is converted into an oscillating boson cloud, which dissipates through the emission of nearly monochromatic gravitational radiation. Thus, gravitational wave observations by ground- or space-based detectors can be used to probe the existence of dark...

We study electroweak phase transition and resultant GWs of a CP conserving 2HDM with a softly broken $Z_2$ symmetry. We analysed the parameter space of both type I and type II 2hdm without relying on any decoupling limit. We observe $M_{H^\pm} \approx M_H$ or $M_{H^\pm} \approx M_A$ favours SFOEWPT in 2HDM. In addition to di-Higgs production, scalar to fermion decay channel is also important...

We study static and spherically symmetric black hole solutions in two classes of vector-tensor theories: generalized Proca theory and Einstein-Aether theory.

We formulate the odd-parity black hole perturbations in these theories by expanding the corresponding action up to second order and discuss whether or not black holes with vector hair suffer ghost or Laplacian instabilities.

We apply...

Inflation generically predicts a gravitational wave background

originating from quantum fluctuations of the space-time metric. I will

discuss quantum gravity models which predict a blue-tilted spectrum,

such as non-local Starobinsky inflation, and present how future

interferometer experiments help to constrain the models.

We review recent results about tests of quantum gravity with

gravitational waves, using modified dispersion relations and the

luminosity distance of standard sirens. Theoretical models predicting

signals observable with LIGO-Virgo-KAGRA and LISA are discussed. The

gravitational-wave physics of a recent nonlocal theory with fractional

operators and infrared corrections to gravity is...

Recent years have seen many publications underlining the importance of space missions to Uranus and Neptune in the following decade. Proposed mission plans would have a cruise time around 10 years, which can be utilized to search for low-frequency gravitational wave signals by observing the Doppler shift in the Earth–spacecraft radio link. Our recent work (Soyuer et al. 2020) demonstrates that...

One natural extension of General Relativity is to introduce a quadratic-curvature correction to the action that is coupled to a scalar field. Such quadratic gravity includes Einstein-dilaton Gauss-Bonnet and dynamical Chern-Simons gravity that are motivated by certain types of string theory. The scalar field induces additional interaction and radiation to compact binary systems. In this talk,...

The science case for a broad program of gravitational wave (GW) detection across all frequency bands is exceptionally strong. At present, there is a dearth of coverage by existing and proposed searches in the GW frequency band lying between the peak sensitivities of PTAs and LISA, roughly 0.1-100 microhertz. In this talk, I will outline a conceptual mission proposal to access this band. I will...

When two black holes merge, the late stage of gravitational wave emission is a superposition of exponentially damped sinusoids. According to the black hole no-hair theorem, this ringdown spectrum depends only on the mass and angular momentum of the final black hole. An observation of more than one ringdown mode can test this fundamental prediction of general relativity. Here we provide strong...