arXiv subjects

Taotao Qiu

Publications and source records attributed to Taotao Qiu.

At least 19 recordsLinked to original sources

arXiv2026

Bounce Inflation with Dynamical Dark Energy in Light of DESI DR2

Recently, the Dark Energy Spectroscopic Instrument Data Release 2 (DESI DR2) suggests that the dark energy in our universe might be evolving, favoring the Chevallier-Polarski-Linder (CPL) parameterization and a lower Hubble constant. In our previous work, it has been reported that cosmological model with the non-singular bounce inflation (BI) scenario and $\Lambda$CDM might alleviate the Hubble tension into 3$\sigma$ confidence. In this paper, we study the cosmological model of BI with a dynamical dark energy. We find that individual consideration of the CPL parameterization and the data \texttt{DESI DR2} tend to larger Hubble constants for both BI and power law (PL) case with cosmic microwave background (CMB) data. Employing BI with combined CPL parameterization and \texttt{DESI DR2}, we obtain the Hubble constant $H_ 0 = 65.2^{ + 1.8}_{ - 2.2} \ \mathrm{km} \cdot \mathrm{s}^{ -1 } \cdot \mathrm{Mpc}^{ -1 }$, which is larger than $H_ 0 = 64.0 \pm 2.1 \ \mathrm{km} \cdot \mathrm{s}^{ -1 } \cdot \mathrm{Mpc}^{ -1 }$ for the PL case. After considering nontrivial weak lensing effect and spatial curvature as well as adding \texttt{Pantheon+}, BI fits 3.1$\sigma$ confidence of $\Lambda$CDM with $w_ 0 = -0.919 \pm 0.038$ and $w_{ \mathrm{a}} = -0.37 \pm 0.12$, and it prefers evolving dark energy than the PL case with $w_ 0 = -0.960 \pm 0.074$ and $w_{ \mathrm{a}} = -0.15^{ +0.28}_{ -0.25}$.

astro-ph.CO↗

arXiv2025

Avoiding PBH overproduction in inflation model with modified dispersion relation

The Pulsar Timing Array (PTA) data of nano-Hertz gravitational waves released in 2023 implies that if such gravitational waves comes from the scalar perturbation induction at the end of inflation, the accompanied primordial black holes (PBHs) will be over-produced, with the fraction exceed the upper bound of unity. This is recognized as the ``overproduction problem", which calls for nontrivial features in the early universe. In this paper, we try to check out whether a modified dispersion relation (MDR) of the primordial perturbations can be helpful for solving the problem. From the constraint on PTA data, we obtain a posterior distribution of the parameters of primordial perturbation, and find that the MDR model, where the $k^4$ term becomes important at later time, can give rise to a broken-power-law (BPL) power spectrum which can alleviate the overproduction problem to nearly $2\sigma$ level. However, to improve furtherly into $1\sigma$ still needs small negative non-Gaussianity, e.g. $f_{\rm nl}\simeq -1$. The mass distribution of the PBHs generated is also discussed.

astro-ph.CO↗

arXiv2025

Parity violation in framework of nonmetricity gravity

The latest observational data of Planck satellite shows nontrivial value of polarization rotation angle caused by cosmic birefringence in the early universe. Moreover, the asymmetry of baryons versus anti-baryons still remains mysterious. Both of them indicates that there should be hidden new physics such as fundamental symmetry breaking. In this paper, we try to interpret these two events in framework of nonmetricity modified gravity. We introduce an interaction term between nonmetricity-based function and matter current, and calculate both the rotation angle and baryon-to-photon ratio. We also constrain the model parameters using the current observational data. With some specific examples, we demonstrate that in nonmetricity gravity theory, these two events can be interpreted in a unified way. Nevertheless, the minimal coupling of nonmetricity scalar and the matter current might not be favored.

astro-ph.CO↗

arXiv2025

The Quintom theory of dark energy after DESI DR2

Observations from DESI DR2 are challenging the $\Lambda$CDM paradigm by suggesting that the equation-of-state parameter of dark energy evolves across $w = -1$, a phenomenon known as the Quintom scenario. Inspired by this development, we present a staged review of Quintom cosmology including its theoretical foundations, observational supports, and implications as well as possible extensions. We first trace the historical progression from Einstein's static cosmological constant to modern dynamical dark energy, summarizing recent cosmological constraints that favor an evolving $w(z)$ along time. A key focus is the theoretical no-go theorem for dark energy showing that no single canonical field or perfect fluid model can smoothly cross the $w = -1$ boundary. We then survey viable Quintom constructions, including two-field models, single-scalar fields with higher derivatives, modified gravity frameworks, interacting dark energy, and an effective field theory approach that unifies these mechanisms. Possible interactions of Quintom fields with ordinary matter and the potential roles in yielding non-singular universe solutions are discussed.

astro-ph.CO↗

arXiv2025

Dynamics of Spinning Test Body in quadratic Einstein-Cartan Theory and its Free-fall Test

We study the dynamics of the non-relativistic spinning test body (STB) in the framework of Einstein-Cartan theory(ECT), in which the weak equivalence principle is violated by the spin-gravitational interaction. We derive the general equation of geodesic in terms of comoving tetrads. More concretely, we consider the case of the quadratic form of the lagrangian, within the environment of weak and static spherically symmetric space-time. We find that the trajectories of STB deviate from the traditional Mathisson\textendash Papapetrou equation, which is due to the coupling of the spin of the test particle to the torsion field of the environment. This allows us to test the theory with free-fall experiment in the laboratory, such as atom interferometer. By using the previous data, we find the upper bound of the possible torsion field on Earth is given by up to $2.0\times 10^{1} \mathrm{~m^{-1}}$ and torsion gradient up to $3.1 \times 10^{-6}\mathrm{~m^{-2}}$. This result may enable us to provide a theoretical foundation for future precision measurements of the existence of the fifth force.

gr-qc↗

arXiv2025

Do JWST reionization (optical depth) puzzle, cosmological tensions, and CMB anomalies imply Harrison-Zel'dovich spectrum?

The James Webb Space Telescope (JWST) has observed massive galaxies at high redshifts, which implies an earlier epoch of reionization (EoR) compared with the cosmic microwave background (CMB) results. In this paper, based on \texttt{Planck 2020} (NPIPE release), \texttt{ACT DR4} and \texttt{SPT-3G} data, if assumed a Harrison-Zel'dovich (HZ) primordial power spectrum in the standard cosmological model, we show that the redshift or optical depth of reionization is larger than the case of a power-law (PL) primordial power spectrum. In HZ-$ \Lambda $CDM model, the redshift of reionization is $ z_\text{reio} = 9.11 \pm 0.61 $, which is consistent with the JWST result that $ z_\text{reio} \approx 8.9 $. Moreover, the cosmological tensions, i.e. Hubble ($H_0$) tension and $ S_8 $ tension are alleviated in HZ-$ \Lambda $CDM case. The Hubble constant is $ H_0 = 70.38 \pm 0.35 \, \text{km}/\text{s}/\text{Mpc}$ and the structure growth parameter is $ S_8 = 0.7645\pm 0.0094 $ in HZ-$ \Lambda $CDM model. We also consider two extensions of $ \Lambda $CDM, including $ \Lambda $CDM$ + A_\text{L} $ and $ \Lambda $CDM$ + \Omega_\text{k} $ models. But the extensions of $ \Lambda $CDM with a HZ spectrum meet more serious CMB anomalies, i.e. lensing anomaly and spatial curvature anomaly as compared with the extensions of $ \Lambda $CDM with a PL spectrum. We discuss that these two CMB anomalies may come from the degeneracy of cosmological parameters.

astro-ph.CO↗

arXiv2024

Primordial Bounce-Inflation Scenario to Alleviate Cosmological Tensions and Lensing Anomaly

We put forward a primordial scenario to alleviate cosmological tensions, i.e. Hubble ($H_0$) tension and $ S_8 $ tension. Based on flat $\Lambda$CDM, the Bounce-Inflation (BI) scenario gives the results that $ H_0 = 68.60^{+0.40}_{-0.45} \, \text{km}/\text{s}/\text{Mpc}$, $ S_8 = 0.806 \pm 0.011 $ by using \texttt{Planck 2018} data sets and $ H_0 = 68.96 \pm 0.38 \, \text{km}/\text{s}/\text{Mpc}$, $ S_8 = 0.797\pm 0.010 $ by using \texttt{Planck 2018} + \texttt{SPT3G} data sets. These reduce the cosmological tensions slightly. We also take an extended $\Lambda$CDM model into account, $\Lambda$CDM (BI)+$A_L$, where $ A_L $ is the gravitational lensing amplitude. The results are $ H_0 = 69.38 \pm 0.49 \, \text{km}/\text{s}/\text{Mpc}$, $ S_8 = 0.774 \pm 0.014 $ fitted by \texttt{Planck 2018} data sets and $ H_0 = 69.49 \pm 0.45 \, \text{km}/\text{s}/\text{Mpc}$, $ S_8 = 0.771^{+0.013}_{-0.012} $ fitted by \texttt{Planck 2018} + \texttt{SPT3G} data sets, which reduce the Hubble tension to $\sim 3\sigma $ level and show no $S_8 $ tension. The $A_L \approx 1.1$ is smaller than the result of the inflation scenario with a constraint of \texttt{Planck 2018} data sets. Besides, the spectral index of the bounce-inflation scenario $ n_s $ is about $ 0.98 $, with a trend to the Harrison-Zel'dovich spectrum.

astro-ph.CO↗

arXiv2024

Interpreting Pulsar Timing Array data of Gravitational Waves with Ekpyrosis-Bouncing Cosmology

Recent pulsar timing array (PTA) experiments have reported strong evidence of the stochastic gravitational wave background (SGWB). If interpreted as primordial Gravitational Waves (pGWs), the signal favors a strongly blue-tilted spectrum. On the other hand, the Ekpyrosis-bouncing cosmology with a strongly blue-tilted GW spectrum, i.e., $n_T \simeq 2$, offers a potential explanation for the observed SGWB signal. In this paper, we construct a concrete Ekpyrosis-bouncing model, and show its capacity to intepret the PTA result without pathologies. Both tensor and scalar perturbations are analysed with constraints from the current observations.

gr-qc↗

arXiv2024

Theoretical and observational constraints on early dark energy in $F(R)$ gravity

This work examines an early dark energy (EDE) scenario in the context of $F(R)$ gravity. EDE is introduced to alleviate the Hubble tension by temporarily injecting approximately $10\%$ of the energy fraction around the matter-radiation equality epoch ($z \approx 10^{3}$--$10^{4}$). Building on several benchmark models, we focus on the potential-driven EDE scenario and investigate the conditions required within $F(R)$ gravity. We first introduce a dimensionless quantity to analytically visualize the evolution of the density ratio between EDE and other matter components. Considering several examples, we demonstrate that the desired EDE can indeed be realized in $F(R)$ gravity. However, stringent constraints arising from violations of the equivalence principle could exclude the allowed parameter space. Our result provides a generic constraint on the potential-driven EDE in $F(R)$ gravity at the background level. This work also concludes that nonperturbative effects or nontrivial mechanisms are indispensable for studying EDE in $F(R)$ gravity while maintaining compatibility with local tests of gravity.

gr-qc↗

arXiv2024

Perturbations of Mimetic Curvaton

The mimetic gravity theory is one of the interesting modified gravity theories, which aims to unify the matter component of our universe within the power of gravity. The mimetic-like theory can also be responsible for primordial perturbations production, e.g., when the mimetic field is set to be like a curvaton field, and the adiabatic perturbation can thus be generated from the isocurvature perturbation via usual curvaton mechanism [1]. In the original mimetic curvaton model, the parameter $λ$ was purely an algebraic multiplier, lack of any perturbed dynamics. In the current paper, we treat $λ$ as an auxiliary field, with its perturbation $δλ$ evolving alongside. We show that, with such a consideration, the adiabatic perturbation can still be generated from the curvaton mechanism, and becomes scale invariant with different field space configurations.

gr-qc↗

arXiv2024

Tensor Perturbations from Bounce Inflation Scenario in f(Q) Gravity

In this paper, we construct a bounce inflation cosmological scenario in the framework of the modified symmetric teleparallel gravity, namely f(Q) theory, and investigate the tensor perturbations therein. As is well-known, the tensor perturbations generated in the very early Universe (inflation and pre-inflation regions) can account for the primordial gravitational waves (PGWs) that are to be detected by the next generation of GW experiments. We discuss the stability condition of the tensor perturbations in the bounce inflation process and investigate in detail the evolution of the perturbation variable. The general form of the tensor power spectrum is obtained both for large as well as small scale modes. As a result, we show for both kinds of modes (short or long wavelength modes), and the tensor spectrum may get a positive tilt in the parametric range where the tensor perturbation proves to be stable -- this interestingly hints an enhancement of gravitational waves' amplitude in the background of the f(Q) bounce-inflation scenario. Moreover, we study the LQC-like scenario as a specific case of our model, in which, the primordial tensor power spectrum turns out to be nearly scale-invariant on both small and large scales.

hep-th↗

arXiv2023

Nonpropagating ghost in covariant $f(Q)$ gravity

$f(Q)$ gravity is an extension of the symmetric teleparallel equivalent to general relativity (STEGR). This work shows that based on the scalar-nonmetricity formulation, a scalar mode in $f(Q)$ gravity has a negative kinetic energy. This conclusion holds regardless of the coincident gauge frequently used in STEGR and $f(Q)$ gravity. To study the scalar mode, we further consider the covariant $f(Q)$ gravity as a special class in higher-order scalar tensor (HOST) theory and rewrite the four scalar fields, which play a role of the Stüeckelberg fields associated with the diffeomorphism, by vector fields. Applying the standard Arnowitt-Deser-Misner (ADM) formulation to the new formulation of the $f(Q)$ gravity, we demonstrate that the ghost scalar mode can be eliminated by the second-class constraints, thus ensuring that $f(Q)$ gravity is a healthy theory.

gr-qc↗

arXiv2023

Generation of primordial black holes from an inflation model with modified dispersion relation

A primordial black hole (PBH) is interesting to people for its ability of explaining dark matter as well as supermassive astrophysical objects. In the normal inflation scenario, the generation of PBHs usually requires an enhanced power spectrum of scalar perturbation at the end of inflation era, which is expected when the dispersion relation of the inflaton field gets modified. In this work, we study a kind of inflation model called {the \it Dirac-Born-Infeld-inspired nonminimal kinetic coupling (DINKIC)} model, where the dispersion relation is modified by a square root existing in the field Lagrangian. We discuss the enhancement of scalar power spectrum due to the modified dispersion relation, as well as the abundance of PBHs produced by the Press-Schechter collapse mechanism. We also discuss the formation of scalar-induced gravitational waves by linear scalar perturbations.

astro-ph.CO↗

arXiv2023

Mimetic Curvaton

In this paper, we investigate the primordial perturbations of inflation model induced from the multi-field mimetic gravity, where there are two field during inflation, and thus both adiabatic and isocurvature perturbation modes are generated. We show that although it is true that the original adiabatic perturbation mode loses the kinetic term due to the constraint equation, by applying the curvaton mechanism where one of the field is viewed as curvaton field, the adiabatic perturbation can actually be transferred from the isocurvature one at the end of inflation. Detailed calculations are performed for both inflationary and the consequent matter-dominant epochs. Therefore, the so-called "non-propagating problem" of the adiabatic mode will actually do no harm to the multi-field mimetic inflation models.

hep-th↗

arXiv2022

Searching for Signal of Primordial Black Hole from CMB Lensing and $γ$-ray Emissions

In this $\textit{Letter}$, we search for the signal of the primordial black holes (PBHs) by correlating the $γ$-ray emissions in the MeV energy band produced by the Hawking evaporation and the lensing effect of the cosmic microwave background (CMB). We use the conservative case of the astrophysical model as much as possible in the calculations, since the potential astrophysical origins dominate the observed emission in the MeV energy band. By carefully discussing the appropriate energy bands corresponding to different PBHs masses, it is worth expecting a tight constraint on the fraction of the Schwarzschild PBHs in the mass range of $10^{16} - 5\times10^{17}\,{\rm g}$, by simulations of the sensitivity of the future CMB-S4 project and the $γ$-ray telescope e-ASTROGAM. Furthermore, we also consider the PBHs model with spins, and find that the constraining ability of the PBHs fraction from the correlation between CMB lensing and $γ$-ray emissions can be improved by another order of magnitude, which could importantly fill the gaps with PBHs fraction limits in the mass range of $5\times 10^{17} - 2\times 10^{18}\,{\rm g}$.

astro-ph.CO↗

arXiv2022

ADM formulation and Hamiltonian analysis of $f(Q)$ gravity

$f(Q)$ gravity is an extension of the symmetric teleparallel equivalent to general relativity. We demonstrate the Hamiltonian analysis of $f(Q)$ gravity with fixing the coincident gauge condition. Using the standard Dirac-Bergmann algorithm, we show that $f(Q)$ gravity has 8 physical degrees of freedom. This result reflects that the diffeomorphism symmetry of $f(Q)$ gravity is completely broken due to the gauge fixing. Moreover, in terms of the perturbations, we discuss the possible mode decomposition of these degrees of freedom.

gr-qc↗

arXiv2022

On Primordial Black Holes and secondary gravitational waves generated from inflation with solo/multi-bumpy potential

It is well known that a primordial black hole (PBH) can be generated in the inflation process of the early universe, especially when the inflation field has a number of non-trivial features that could break the slow-roll condition. In this study, we investigate a toy model of inflation with bumpy potential, which has one or several bumps. We determined that the potential with multi-bump can generate power spectra with multi-peaks in small-scale region, which can in turn predict the generation of primordial black holes in various mass ranges. We also consider the two possibilities of PBH formation by spherical and elliptical collapses. Finally, we discuss the scalar-induced gravitational waves(SIGWs)generated by linear scalar perturbations at second order.

astro-ph.CO↗

arXiv2022

Can the Quantization of Black Hole be detected?

As a mysterious celestial body predicted by General Relativity, black holes have been confirmed by observations in recent years. But there are still many unknown properties waiting for us to discover, one of the famous problems is the quantization of black holes. The quantization of black holes gives new research significance to black holes, but the quantization of black holes is difficult to prove. Here we propose a new method to verify the quantization of black holes: Carnot cycle. Our results show that if the black holes have quantized energy levels, the work W they impose to us via the Carnot cycle should also be quantized. We indirectly verify the quantization of black holes by detecting the quantization of W, and contrast it with the classic Carnot cycle. In addition, we have also verified the correctness of the second law of thermodynamics under the premise of considering the quantization of black holes.

gr-qc↗