arXiv subjects

Daisuke Yamauchi

Publications and source records attributed to Daisuke Yamauchi.

At least 19 recordsLinked to original sources

arXiv2026

Stability and quasi-normal ringing in analogue black-white holes in SNAIL-based traveling-wave parametric amplifiers

The circuit dynamics constructed by traveling-wave parametric amplifiers (TWPA), using superconducting nonlinear asymmetric elements (SNAILs), are known to be approximately described by the Korteweg-de Vries (KdV) or modified KdV equations in the continuum limit and admit soliton solutions. The soliton spatially modulates the effective propagation velocity of the weak probe field, which leads to the effective realization of the causal structure of the analogue event horizons in the SNAIL-TWPA circuit system. In this paper, we derive the master equation for the weak probe field where the background soliton acts as an effective potential. We show the absence of normalizable negative modes in the SNAIL-TWPA circuit system by using the language of supersymmetric quantum mechanics. We also present the first study of quasi-normal modes (QNM) of the SNAIL-TWPA analogue black-white hole system by semi-analytic and numerical methods. Based on the resultant QNM frequency, we clarify the timescale at which nonlinear dispersion becomes effective in the SNAIL-TWPA circuit system and demonstrate how ringdown is excited.

gr-qc↗

arXiv2026

Imprints of flat space analyticity in de Sitter S-matrix

The analytic structure of the flat-space S-matrix provides non-perturbative constraints on low-energy effective field theories based on the properties of high-energy theory. While the analytic structure of the flat-space S-matrix is well understood, extending this framework to de Sitter space is challenging, as the expanding background complicates the definition of asymptotic states and breaks time-translation symmetry. This paper investigates how flat-space analyticity is imprinted on the de Sitter S-matrix. We derive a relation between flat-space amplitude and de Sitter S-matrix on a specific limit called the Hubble flat-space limit. Specifically, we show that the relation holds for tree-level amplitude exchanging a massive scalar field with any local derivative interactions. Finally, we argue that the Hubble flat-space limit is more compatible with the description of effective field theory, as the total energy dependence of de Sitter S-matrix becomes trivial, allowing the Mandelstam variable to be identified as the unique energy scale, just as in flat space.

hep-th↗

arXiv2024

Kurtosis consistency relation in large-scale structure as a probe of gravity theories

Various gravity theories beyond general relativity have been rigorously investigated in the literature such as Horndeski and degenerate higher-order scalar-tensor (DHOST) theories. In general, numerous model parameters are involved in such theories, which should be constrained to test the theories with experiments and observations. We construct the kurtosis consistency relations, calculated based on matter density fluctuations, in which the information of gravity theories is encoded. We derive two independent consistency relations that should hold in the framework of the DHOST theories and argue that such consistency relations would be useful for testing gravity theories.

astro-ph.CO↗

arXiv2024

Tensor clustering fossils in modified gravity and high-redshift gravitational-wave sound speed

We investigate the tensor clustering fossils as a possible probe to constrain the theory of gravity, in particular the deviation of the sound speed of gravitational waves from the speed of light at high redshifts. We develop the formalism of the effective Poisson equation to include the novel phenomenological model of the scalar-tensor tidal interactions that are expected to be induced by the modification of the theory of gravity. We show that the tensor clustering fossils can arise from the propagation of gravitational waves, the growth of the large-scale structures, and the second-order contributions from the effective Poisson equation. We construct the small-scale effective Lagrangian from the Horndeski scalar-tensor theory and derive the formula applicable to the tensor clustering fossils in the language of the effective field theory of dark energy. As a demonstration, we apply the formalism to the constraint on the sound speed of gravitational waves in the futuristic survey.

astro-ph.CO↗

arXiv2024

Dynamical simulations of colliding superconducting strings

We study the collisions of elastic superconducting strings, also referred to as current-carrying strings, formed in a $U_{\rm local}(1) \times U_{\rm global}(1)$ field-theory model, using three-dimensional numerical field-theoretic simulations. The breaking of $U_{\rm local}(1)$ leads to string formation via the Higgs mechanism, while the scalar field of the second $U_{\rm global}(1)$ carries the current, which condenses onto the string. We construct straight and static superconducting string solutions numerically and identify the regions in which they exist in the model parameter space. We then perform dynamical simulations for colliding superconducting strings with various collision angles and collision velocities. We explore the kinematic parameter space for six sets of model parameters characterising the coupling between the two scalar fields and the current on the string. The final states of the strings (after the collision) are reported diagrammatically. We classify them into four categories: (i) regular intercommutation, (ii) double intercommutation, (iii) bound state, and (iv) expanding string solution. We find that the outcome of the collision process is the regular intercommutation of the colliding strings in most of the kinematic parameter space while they form bound states for small velocities and small angles. We also find that the strings undergo two successive intercommutations and, therefore, pass through one other in a small region corresponding to relatively small angles and velocities of order c/2. The string structure breaks down when there is a relatively large coupling between the two scalar fields, even if each string is stable before the occurrence of the collision.

hep-ph↗

arXiv2023

Axion Cloud Decay due to the Axion-photon Conversion with Multi-pole Background Magnetic Fields

We consider axion cloud decay due to the axion-photon conversion with multi-pole background magnetic fields. We focus on the $\ell=m=1$ and $n=2$ mode for the axion field configuration since it has the largest growth rate associated with superradiant instability. Under the existence of a background multi-pole magnetic field, the axion field can be converted into the electromagnetic field through the axion-photon coupling. Then the decay rate due to the dissipation of the converted photons is calculated in a successive approximation. We found that the decay rate is significantly dependent on the azimuthal quantum number characterizing the background magnetic field, and can be comparable to or larger than the growth rate of the superradiant instability.

hep-ph↗

arXiv2023

Dark age consistency in the 21cm global signal

We propose a new observable for the 21cm global signal during the dark ages, the dark-age consistency ratio, which is motivated from the fact that the shape of the functional form of the brightness temperature against the frequency is cosmological-parameter independent in the standard $Λ$CDM model. The dark-age consistency ratio takes a certain definite value in the $Λ$CDM case, which can serve as a critical test of the model and probe those beyond the standard one. The new observable just needs measurements of the brightness temperature at a few frequency bands during the dark ages, and thus it allows us to test cosmological scenarios even with limited information on the global signal.

astro-ph.CO↗

arXiv2023

Ostrogradsky mode in scalar-tensor theories with higher-order derivative couplings to matter

A metric transformation is a tool to find a new theory of gravity beyond general relativity. The gravity action is guaranteed to be free from a dangerous Ostrogradsky mode as long as the metric transformation is regular and invertible. Various degenerate higher-order scalar-tensor theories (DHOST) without extra degrees of freedom have been found through the metric transformation with a scalar field and its derivatives. In this work, we examine how a matter coupling changes the degeneracy for a theory generated from the Horndeski theory through the metric transformation with the second derivative of a scalar field, taking a minimally-coupled free scalar field as the matter field. When the transformation is invertible, this theory is equivalent to the Horndeski theory with a higher-order derivative coupling to the matter scalar field. Working in this Horndeski frame and the unitary gauge, we find that the degeneracy conditions are solvable and the matter metric must have a certain structure to remove the Ostrogradsky mode.

gr-qc↗

arXiv2023

First test of the consistency relation for the large-scale structure using the anisotropic three-point correlation function of BOSS DR12 galaxies (An explanatory video is available at https://youtu.be/Zi36ooLPhss.)

We present, for the first time, an observational test of the consistency relation for the large-scale structure (LSS) of the Universe through a joint analysis of the anisotropic two- and three-point correlation functions (2PCF and 3PCF) of galaxies. We parameterise the breakdown of the LSS consistency relation in the squeezed limit by $E_{\rm s}$, which represents the ratio of the coefficients of the shift terms in the second-order density and velocity fluctuations. $E_{\rm s}\neq1$ is a sufficient condition under which the LSS consistency relation is violated. A novel aspect of this work is that we constrain $E_{\rm s}$ by obtaining information about the nonlinear velocity field from the quadrupole component of the 3PCF without taking the squeezed limit. Using the galaxy catalogues in the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12, we obtain $E_{\rm s} = -0.92_{-3.26}^{+3.13}$, indicating that there is no violation of the LSS consistency relation in our analysis within the statistical errors. Our parameterisation is general enough that our constraint can be applied to a wide range of theories, such as multicomponent fluids, modified gravity theories, and their associated galaxy bias effects. Our analysis opens a new observational window to test the fundamental physics using the anisotropic higher-order correlation functions of galaxy clustering.

astro-ph.CO↗

arXiv2023

New constraints on cosmological modified gravity theories from anisotropic three-point correlation functions of BOSS DR12 galaxies

We report a new test of modified gravity theories using the large-scale structure of the Universe. This paper is the first attempt to (1) apply a joint analysis of the anisotropic components of galaxy two- and three-point correlation functions (2 and 3PCFs) to actual galaxy data and (2) constrain the nonlinear effects of degenerate higher-order scalar-tensor (DHOST) theories on cosmological scales. Applying this analysis to the Baryon Oscillation Spectroscopic Survey (BOSS) data release 12, we obtain the lower bounds of $-1.655 < ξ_{\rm t}$ and $-0.504 < ξ_{\rm s}$ at the $95\%$ confidence level on the parameters characterising the time evolution of the tidal and shift terms of the second-order velocity field. These constraints are consistent with GR predictions of $ξ_{\rm t}=15/1144$ and $ξ_{\rm s}=0$. Moreover, they represent a $35$-fold and $20$-fold improvement, respectively, over the joint analysis with only the isotropic 3PCF. We ensure the validity of our results by investigating various quantities, including theoretical models of the 3PCF, window function corrections, cumulative ${\rm S/N}$, Fisher matrices, and statistical scattering effects of mock simulation data. We also find statistically significant discrepancies between the BOSS data and the Patchy mocks for the 3PCF measurement. Finally, we package all of our 3PCF analysis codes under the name \textsc{HITOMI} and make them publicly available so that readers can reproduce all the results of this paper and easily apply them to ongoing future galaxy surveys.

astro-ph.CO↗

arXiv2023

Probing the primordial Universe with 21-cm line from cosmic dawn/epoch of reionization

In the most distant reaches of the Universe, the 21-cm hyperfine transition in neutral hydrogen provides one of the only available tracers of large-scale structure. A number of instruments have been working and planned to measure the 21-cm line signals, and in particular, Experiment to Detect the Global EoR Signature (EDGES) recently has reported the first detection of an absorption signal, which corresponds to the 21-cm line global signal at the epoch of reionization (EoR). The future large radio telescope, Square Kilometre Array (SKA) will be able to deliver the high-precision measurement of 21-cm line emission/absorption signals. In this paper, we review the current status for the 21-cm line global and fluctuation signals from EoR to the dark ages, and then summarize the recent studies of how we probe the primordial Universe particularly motivated by the recent EDGES result and future observations by SKA. We focus on two applications for constraining cosmology with the EDGES result: constraints on the primordial magnetic fields and those on the primordial power spectrum. We also discuss the potential of future SKA for probing the inflationary Universe, by discussing expected constraints on the primordial power spectrum, its adiabaticity, and primordial non-Gaussianities from future observations of 21-cm fluctuations.

astro-ph.CO↗

arXiv2023

Skewness consistency relation in large-scale structure and test of gravity theory

We investigate the skewness of galaxy number density fluctuations as a possible probe to test gravity theories. We find that the specific linear combination of the skewness parameters corresponds to the coefficients of the second-order kernels of the density contrast, which can be regarded as the consistency relation and used as a test of general relativity and modified gravity theories. We also extend the analysis of the skewness parameters from real space to redshift space and derive the redshift-space skewness consistency relation.

astro-ph.CO↗

arXiv2022

Cosmological gravity probes: connecting recent theoretical developments to forthcoming observations

Since the discovery of the accelerated expansion of the present Universe, significant theoretical developments have been made in the area of modified gravity. In the meantime, cosmological observations have been providing more high-quality data, allowing us to explore gravity on cosmological scales. To bridge the recent theoretical developments and observations, we present an overview of a variety of modified theories of gravity and the cosmological observables in the cosmic microwave background and large-scale structure, supplemented with a summary of predictions for cosmological observables derived from cosmological perturbations and sophisticated numerical studies. We specifically consider scalar-tensor theories in the Horndeski and DHOST family, massive gravity/bigravity, vector-tensor theories, metric-affine gravity, and cuscuton/minimally-modified gravity, and discuss the current status of those theories with emphasis on their physical motivations, validity, appealing features, the level of maturity, and calculability. We conclude that the Horndeski theory is one of the most well-developed theories of modified gravity, although several remaining issues are left for future observations. The paper aims to help to develop strategies for testing gravity with ongoing and forthcoming cosmological observations.

astro-ph.CO↗

arXiv2022

Signature of primordial non-Gaussianity on 21-cm power spectrum from dark ages

We study the signature of primordial non-Gaussianity imprinted on the power spectrum of the 21-cm line differential brightness temperature during dark ages. Employing the perturbative treatment of gravitational clustering, we quantitatively estimate the effects of the non-Gaussian and one-loop corrections on the 21-cm power spectrum. The potential impact of the use of the 21-cm power spectrum for the constraint on local-type primordial non-Gaussianity is investigated based on the Fisher matrix analysis. Our results show that the 21-cm power spectrum for an array with a baseline of several tens of kilometers can constrain the primordial non-Gaussianity to a level severer than that from cosmic microwave background measurements and its constraining power is stronger than that of the 21-cm bispectrum, while in the ultimate situation the 21-cm bispectrum eventually becomes more powerful.

astro-ph.CO↗

arXiv2022

Second-order peculiar velocity field as a novel probe of scalar-tensor theories

We investigate the galaxy bispectrum induced by the nonlinear gravitational evolution as a possible probe to constrain degenerate higher-order scalar tensor (DHOST) theories. We find that the signal obtained from the leading kernel of second-order density fluctuations is partially hidden by the uncertainty in the nonlinear galaxy bias, and that the kernel of second-order velocity fields instead provides unbiased information on the modification of gravity theory. Based on this fact, we propose new phenomenological time-dependent functions, written as a combination of the coefficients of the second-order kernels, which is expected to trace the higher-order growth history. We then present approximate expressions for these variables in terms of parameters that characterize the DHOST theories. We also show that the resultant formulae provides new constraints on the parameter space of the DHOST theories.

astro-ph.CO↗

arXiv2022

Testing the Non-circularity of the Spacetime around Sagittarius A* with Orbiting Pulsars

A disformal Kerr black hole solution is a rotating black hole solution in a modified gravity theory which breaks the circular condition of spacetime differently from the case of the Kerr spacetime. In this paper, assuming that Sagittarius A* (Sgr A*) is a disformal Kerr black hole, we examine the potential to test the spacetime geometry with a hypothetical pulsar whose orbital elements are similar to those of the S2/S0-2 star. By numerically solving the equations of motion for the pulsar and photons emitted from it, we calculate the apparent position of the pulsar and the time of arrival (TOA) of the emitted pulse signals. Our analysis shows that the magnitude of the difference in the TOAs reaches the order of $10\>{\rm ms}$ if the deviation from the Kerr spacetime is significant. The time difference is mainly caused by the non-circularity of the spacetime at the $1.5$ post-Newtonian order. The accuracy of the TOA measurement by a future radio telescope named the Square Kilometer Array (SKA) is between about $0.1\>{\rm ms}$ and $10\>{\rm ms}$ for a normal pulsar. Thus, we expect that the SKA can distinguish the disformal Kerr black hole from the Kerr black hole through the non-circularity of the spacetime around Sgr A*.

gr-qc↗

arXiv2021

Generalized local ansatz for scale-dependent primordial non-Gaussianities and future galaxy surveys

We revisit a possible scale-dependence of local-type primordial non-Gaussianities induced by super-horizon evolution of scalar field perturbations. We develop the formulation based on $δN$ formalism and derive the generalized form of the local-type bispectrum and also trispectrum which allows us to implement the scale-dependence and suitably compare model prediction with observational data. We propose simple but phenomenologically meaningful expressions, which encompass the information of a wide range of physically motivated models. We also formulate large-scale power spectrum and bispectrum of biased objects in the presence of the scale-dependent primordial non-Gaussianities. We perform the Fisher analysis for future galaxy surveys and give the projected constraints on the parameters of the generalized local-form of primordial non-Gaussianities.

astro-ph.CO↗

arXiv2021

Unified approach to secondary effects on the CMB B-mode polarization

We develop a systematic and unified approach to estimate all possible secondary (i.e. non-primordial) nonlinear effects to the cosmic microwave background (CMB) polarization, named curve-of-sight integration approach. In this approach, the Boltzmann equation for polarized photons is rewritten in a line-of-sight integral along an exact geodesic in the perturbed universe, rather than a geodesic in the background universe used in the linear-order CMB calculation. This approach resolves the difficulty to solve the Boltzmann hierarchy with the nonlinear gravitational effects in the photon free-streaming regime and thus unifies the standard remapping approach for CMB lensing into the direct approach solving the Boltzmann equation for the nonlinear collisional effects. In this paper, we derive formulae that: (i) include all the nonlinear effects; (ii) can treat extended sources such as the contributions after the reionization. It offers a solid framework to discuss possible systematics in the standard estimation of CMB lensing by the remapping approach. As an explicit demonstration, we estimate the secondary B-mode power spectrum induced by all foreground gravitational effects: lensing, redshift, time-delay, emission-angle, and polarization-rotation effects. We define these effects properly so that they do not have any overlap, also without overlooking any effect. Then, we show that these effects only give corrections of the order of 0.001-0.01% to the standard lensing-induced B-mode power spectrum in the concordance $Λ$ cold dark matter model. Our result confirms the reliability of using the remapping approach in upcoming CMB experiments aiming to detect the primordial gravitational waves with the tensor-to-scalar ratio of $r \sim 10^{-3}$.

astro-ph.CO↗