arXiv subjects

Lian-Tao Wang

Publications and source records attributed to Lian-Tao Wang.

At least 19 recordsLinked to original sources

arXiv2026

Probing Inflationary Origins of Primordial Black Holes with LIGO--Virgo--KAGRA O1--O4a data

Large primordial curvature perturbations not only produce primordial black holes (PBHs) but also inevitably source a scalar-induced stochastic gravitational-wave background upon horizon reentry. We analyze the combined LIGO--Virgo--KAGRA O1--O4a data to constrain two representative inflationary mechanisms for generating such perturbations: ultra-slow-roll inflation and an inflationary phase transition. Detecting no evidence for either scenario, we place 95% credible upper limits on the curvature-spectrum amplitude across the frequency range accessible to ground-based interferometers. Translated into the PBH context, these limits already exceed conventional constraints, probing abundance fractions far below unity. Our results remain robust even when the PBHs themselves are too rare to be directly detected or have evaporated. This work demonstrates that stochastic gravitational-wave observations offer a powerful and complementary probe of small-scale inflationary physics and PBH formation, with upcoming interferometers promising to extend sensitivity to a wider range of inflationary epochs and PBH masses.

astro-ph.CO↗

arXiv2026

Perturbative Dissipation in Minimal Warm Inflation

We present an analysis of the perturbative modes of dissipation in the minimal warm inflation model where an axion-inflaton is coupled to a gluon thermal bath through the axion-gauge coupling. The corresponding friction coefficient, which generically is governed by IR physics, for the processes we consider is dominated by Landau damping of soft space-like gluons and the plasmon decay of hard on shell gluons. Since both of these processes are IR dominated, the friction coefficient becomes sensitive to the non-perturbative magnetic mass scale $m_{g}^{-1} \sim (αT)^{-1}$ which in turn leads to the friction coefficient's overall linear proportionality to $α$, which is much less suppressed in $α$ powers compared to the well understood term from Chern-Simons (CS) diffusion $(\propto α^5)$. On the other hand, this contribution to the friction coefficient is suppressed due to slow roll. We show that this can be viewed as a suppression of local spontaneous CPT violation for derivative couplings in general and that time correlations of nonlocal variables which do not fall off at large time separations are what allow an unsuppressed friction coefficient.

hep-ph↗

arXiv2026

Suppressed Quantum Effects of Weakly Coupled Waves

Precision experiments increasingly target weakly coupled waves, including axion dark matter and gravitational radiation. Such waves are commonly described as classical fields, yet they could exist in quantum states with no classical counterpart. We exhibit two severe obstructions to detecting nonclassical effects, both independent of the mode occupancy. First, realistic detectors cannot resolve the fundamental modes of a field; instead they couple to coarse-grained "effective" modes, which often washes out nonclassical effects. Second, all nonclassical effects are suppressed by extra powers of the weak coupling, making them much harder to detect than the waves themselves. We prove this in general, and explicitly show how the suppression arises for quadrature and number statistics, entanglement, and decoherence. The suppression can in principle be overcome given suitable quantum resources, such as highly squeezed detector states, but the required parameters are far beyond current experimental capabilities. We use the axion cavity haloscope as an explicit example, although our conclusions apply to many ultralight dark matter searches, and rule out proposals to establish the quantization of gravity from observations of gravitational waves.

hep-ph↗

arXiv2026

Searching Stochastic Gravitational Wave Background Landscape Across Frequency Bands

Gravitational wave (GW) astrophysics is entering a multi-band era with upcoming GW detectors, enabling detailed mapping of the stochastic GW background across vast frequencies. We highlight this potential via a new physics scenario: hybrid topological defects from a two-step phase transition separated by inflation. We develop a general pipeline to analyze experimental exclusions and apply it to this model. The model offers a possible explanation of the pulsar timing array signal at low frequencies, and future experiments (LISA/Cosmic Explorer/Einstein Telescope) will confirm or rule it out via the higher-frequency probes, showcasing the power of multi-band constraints.

gr-qc↗

arXiv2026

A Busy Higgs Signal

Higgs final states are prime targets in the search for physics beyond the Standard Model. In the conventional picture, $SU(2)$ symmetry together with the Goldstone Equivalence Theorem correlates Higgs and gauge-boson final states, implying comparable sensitivity in channels such as $hh$, $ZZ$, and $WW$ in searches for heavy resonances. In this work, we identify a mechanism to parametrically violate this expectation. We show that higher-order Higgs couplings can induce an electroweak-symmetry-breaking enhancement that selectively amplifies Higgs-rich final states, allowing them to become the leading discovery channels of new resonances. For scalar resonances, this can make di-Higgs the dominant bosonic signal. For resonance masses higher than a couple of TeV, it also opens resonant tri-Higgs and four-Higgs channels as well-motivated search targets. The same underlying mechanism extends to heavy fermionic and vector resonances, where it can similarly enhance channels such as $ht$, $Zh$, and $γh$. We present this framework in effective field theory, demonstrate possible UV completions, and discuss its implications for collider searches.

hep-ph↗

arXiv2026

Uncool soft-wall transitions and gravitational waves

Theories with warped extra dimensions, like the Randall-Sundrum (RS) model, exhibit a holographic phase transition from a hot, deconfined black brane phase to a cool, confined phase. The standard picture of a first-order, strongly supercooled phase transition is expected to change in variations where the extra dimension is smoothly cut off by a soft-wall curvature singularity, as opposed to a hard brane. To understand this situation, we consider a simple ansatz for the warped geometry which allows us to obtain analytical results while maintaining the essential behavior of a soft wall. Unlike RS with the usual Goldberger-Wise stabilization, the hot, black brane phase only exists above a minimum temperature, which is not much smaller than the critical temperature. We explore the dynamics of the phase transition across the range of possibilities for the asymptotic geometry of a soft wall. This involves calculating an effective 4D action for the location of the black brane horizon. Using the effective action, we show that the phase transition completes rapidly ($β/H$ of $10^{3\text{-}4}$ is typical) and with only slight supercooling. We compute the resulting gravitational wave signal for a TeV-scale transition, finding that it is accessible to future space-based interferometers.

hep-ph↗

arXiv2025

Landscapes at Colliders

Theories with a large number of long-lived metastable vacua are our only concrete explanation for the puzzling value of the Cosmological Constant (CC). The energy scales where these vacua are realized are unknown. In this work, we consider the possibility that a sector of this landscape of vacua is within experimental reach and discuss its signatures at colliders. We find that striking large-multiplicity final states might have gone undetected due to their relatively small total energy. In particular, this could lead to new exotic Higgs decays, which are both intriguing and challenging to search for. In addition to a general phenomenological analysis of these theories, we also discuss an explicit model where the small values of the CC and the Higgs mass are jointly explained by Weinberg's anthropic argument and a low energy landscape.

hep-ph↗

arXiv2025

Anatomy of Parity-violating Trispectra in Galaxy Surveys

Parity-violating interactions are ubiquitous phenomena in particle physics. If they are significant during cosmic inflation, they can leave imprints on primordial perturbations and be observed in correlation functions of galaxy surveys. Importantly, parity-violating signals in the four-point correlation functions (4PCFs) cannot be generated by Einstein gravity in the late universe on large scales, making them unique and powerful probes of high-energy physics during inflation. However, the complex structure of the 4PCF poses challenges in diagnosing the underlying properties of parity-violating interactions from observational data. In this work, we introduce a general framework that provides a streamlined pipeline directly from a particle model in inflation to galaxy 4PCFs in position space. We demonstrate this framework with a series of toy models, effective-field-theory-like models, and full models featuring tree-level exchange-type processes with chemical-potential-induced parity violation. We further showed the detection sensitivity of these models from BOSS data and highlighted potential challenges in data interpretation and model prediction.

astro-ph.CO↗

arXiv2025

Phase transition during inflation and the gravitational wave signal at pulsar timing arrays

The gravitational wave (GW) signal offers a promising window into the dynamics of the early universe. The recent results from the pulsar timing arrays (PTAs) could be the first glimpse of such new physics. In particular, they could point to new details during inflation, which can not be probed by other means. We explore the possibility that the new results could come from the secondary GWs sourced by curvature perturbations, generated by a first-order phase transition during inflation. Based on the results of a field-theoretic lattice simulation of the phase transition process, we show that the GW signal generated through this mechanism can account for the new results from the PTAs. We analyze the spectral shape of the signal in detail. Future observations can use such information to distinguish the GW signal considered here from other possible sources.

astro-ph.CO↗

arXiv2025

Decoherence in high energy collisions as renormalization group flow

The unification of quantum information science and collider physics is opening a new frontier in high-energy experiments, making a systematic understanding of decoherence a critical challenge. We present a framework to systematically compute spin decoherence from final-state radiation by combining soft-collinear effective theory and open quantum system techniques. We demonstrate that the renormalization group (RG) evolution of the final-state spin density matrix constitutes a quantum channel, where the RG flow parameter, rather than time, drives a Markovian loss of quantum information. Our approach incorporates explicit detector resolution parameters, allowing a direct connection between experimental capabilities and the preservation of quantum coherence. Applying this formalism to a fermion pair ($f\bar{f}$) in the high-energy limit with QED-like final-state radiation, we provide the first systematically RG-improved prediction for decoherence as a function of experimental resolution, revealing the underlying decoherence mechanism to be a phase-flip channel. This work establishes an essential theoretical tool for future precision measurements of quantum phenomena in high-energy collisions and offers a new perspective on the interplay between RG flow and decoherence of open quantum systems.

hep-ph↗

arXiv2025

Intrinsically Quantum Effects of Axion Dark Matter are Undetectable

Is the usual treatment of axion dark matter as a classical field reliable? We show that the answer is subtle: the axion field could well be in a quantum state that has no complete classical description, but realistic detectors cannot tell the difference. To see this, we solve a fully quantum model of axion detection using quantum optics techniques. We show that intrinsically quantum effects are washed out by mode averaging or small amounts of noise, and significantly suppressed by the weakness of the axion coupling. Our work exemplifies that there should always be a classical analog for axion dark matter effects, extends to other wave (ultralight) dark-matter candidates, and gives a general method to compute the effects of exotic dark-matter states.

hep-ph↗

arXiv2025

Anisotropic Gravitational Waves from Anisotropic Axion Rotation

Gravitational waves (GWs) provide a powerful probe of the early universe due to their ability to free-stream across cosmic history. We study GW production in a compelling scenario where a rotating axion(-like) field becomes relevant for a brief period in the early universe before transitioning into a kination fluid and rapidly dissipating its energy through cosmic expansion. During this short epoch, the curvature perturbation can be predominantly sourced by the rotating axion and may significantly exceed the adiabatic component. Moreover, axion field perturbations grow on superhorizon scales during this phase. These effects can generate a strong stochastic background of induced GWs. This GW background also exhibits a pronounced large-scale anisotropy inherited from the axion fluctuations, serving as a distinctive signature of the scenario. Importantly, the transient nature of axion relevance enables this scenario to evade stringent bounds on large-scale perturbations. We analyze various observational constraints and find that both the amplitude and anisotropy of the resulting GW signal could be accessible to future detectors.

hep-ph↗

arXiv2025

Probing Primordial Power Spectrum and Non-Gaussianities With Fast Radio Bursts

We use the precision measurements of the arrival time differences of the same fast radio burst (FRB) source along multiple sightlines to measure the primordial power spectrum and Non-Gaussianities. The anticipated experiment requires a sightline separation of 100 AU, achieved by sending three or more radio telescopes to the outer solar system. The Shapiro time delays, measured relatively between different telescopes, are sensitive to the gradient field of the gravitational potential between different sightlines. Since the arrival time difference is independent of when the transient signal is emitted from the source, every measurement of the detected FRB source can be correlated. With enough FRB sources discovered, we can map the gravitational potential across the sky. We further calculate the two-point and three-point correlation function of the arrival time difference between telescopes for different FRB sources in the sky. If $10^4$ FRBs were to be detected, our results suggest that this technique can test the inflationary scale-invariant power spectrum down to $\sim 10^3\,\rm Mpc^{-1}$ and primordial Non-Gaussianities at a level of $f_{\rm NL}\sim 1$.

astro-ph.CO↗

arXiv2025

Acoustic Misalignment Mechanism for Axion Dark Matter

A rotation in the field space of a complex scalar field corresponds to a Bose-Einstein condensation of $U(1)$ charges. We point out that fluctuations in this rotating condensate exhibit sound-wave modes, which can be excited by cosmic perturbations and identified with axion fluctuations once the $U(1)$ charge condensate has been sufficiently diluted by cosmic expansion. We consider the possibility that these axion fluctuations constitute dark matter and develop a formalism to compute its abundance. We carefully account for the growth of fluctuations during the epoch where the complex scalar field rotates on the body of the potential and possible nonlinear evolution when the fluctuations become non-relativistic. We find that the resultant dark matter abundance can exceed the conventional and kinetic misalignment contributions if the radial direction of the complex scalar field is sufficiently heavy. The axion dark matter may also be warm enough to leave imprints on structure formation. We discuss the implications of this novel dark matter production mechanism -- {\it acoustic misalignment mechanism} -- for the axion rotation cosmology, including kination domination and baryogenesis from axion rotation, as well as for axion searches.

hep-ph↗

arXiv2025

A Quantum Description of Wave Dark Matter

We outline a fundamentally quantum description of bosonic dark matter (DM) from which the conventional classical-wave picture emerges in the limit $m \ll 10~\textrm{eV}$. As appropriate for a quantum system, we start from the density matrix which encodes the full information regarding the possible measurements we could make of DM and their fluctuations. Following fundamental results in quantum optics, we argue that for DM it is most likely that the density matrix takes the explicitly mixed form of a Gaussian over the basis of coherent states. Deviations from this would generate non-Gaussian fluctuations in DM observables, allowing a direct probe of the quantum state of DM. Our quantum optics inspired approach allows us to rigorously define and interpret various quantities that are often only described heuristically, such as the coherence time or length. The formalism further provides a continuous description of DM through the wave-particle transition, which we exploit to study how density fluctuations over various physical scales evolve between the two limits and to reveal the unique behavior of DM near the boundary of the wave and particle descriptions.

hep-ph↗

arXiv2024

Monopole Catalyzed Baryogenesis with a $θ$ angle

Monopoles are generally expected in Grand Unified Theories (GUTs) where they can catalyze baryon decay at an unsuppressed rate by the Callan-Rubakov effect. For the first time, we show this catalysis effect can generate the observed baryon asymmetry at GeV scale temperatures. We study the minimal SU(5) GUT model and demonstrate that monopoles-fermion scattering with a $CP$-violating $θ$-term leads to realistic baryogenesis even when $θ\lesssim 10^{-10}$ is below the neutron EDM bound, potentially detectable in the future measurements. Our calculation also shows that to generate the observed baryon asymmetry, the abundance of the monopoles is below the current experiential bounds.

hep-ph↗

arXiv2024

Crescendo Beyond the Horizon: More Gravitational Waves from Domain Walls Bounded by Inflated Cosmic Strings

Gravitational-wave (GW) signals offer a unique window into the dynamics of the early universe. GWs may be generated by the topological defects produced in the early universe, which contain information on the symmetry of UV physics. We consider the case in which a two-step phase transition produces a network of domain walls bounded by cosmic strings. Specifically, we focus on the case in which there is a hierarchy in the symmetry-breaking scales, and a period of inflation pushes the cosmic string generated in the first phase transition outside the horizon before the second phase transition. We show that the GW signal from the evolution and collapse of this string-wall network has a unique spectrum, and the resulting signal strength can be sizeable. In particular, depending on the model parameters, the resulting signal can show up in a broad range of frequencies and can be discovered by a multitude of future probes, including the pulsar timing arrays and space- and ground-based GW observatories. As an example that naturally gives rise to this scenario, we present a model with the first phase transition followed by a brief period of thermal inflation driven by the field responsible for the second stage of symmetry breaking. The model can be embedded into a supersymmetric setup, which provides a natural realization of this scenario. In this case, the successful detection of the peak of the GW spectrum probes the soft supersymmetry breaking scale and the wall tension.

hep-ph↗

arXiv2024

Towards a Complete Treatment of Scalar-induced Gravitational Waves with Early Matter Domination

Large curvature perturbations can source an observable amount of stochastic gravitational wave background (SGWB). We consider several scenarios where small-scale curvature perturbations are naturally enhanced due to the presence of additional spectator fields during inflation. The same spectator fields can lead to a period of early matter domination (EMD) after inflation. We compute the inflationary spectrum of curvature perturbation and determine its evolution at later times, taking into account both the onset and the end of the EMD epoch, and also the impact of relative velocity perturbation between matter and radiation. The feature that the same field is responsible for both enhanced perturbations and the EMD era, leads to a predictive framework within which the full frequency dependence of SGWB can be computed. The SGWB can be observed in several detectors, including those focused on the nano-Hz regime. Our numerical framework can also be used to study other non-standard cosmological histories.

gr-qc↗