arXiv subjects

Sibo Zheng

Publications and source records attributed to Sibo Zheng.

At least 19 recordsLinked to original sources

arXiv2026

Revisiting the Hubble tension with an inverse power-law early dark energy

We propose a new early dark energy with a potential that has an inverse power-law asymptotic tail to alleviate the Hubble tension. Fitting this model to the datasets of CMB+BAO+SN+H0DN, one obtains a 68$\%$ confidence-level value of $H_0\sim 70.20^{+0.60}_{-0.47}$ km s$^{-1}$Mpc$^{-1}$ and a best-fit value of $H_0\sim 70.56$ km s$^{-1}$Mpc$^{-1}$ for index $n=10$. We show that this model can be tested by future data of CMB and matter power spectra. Finally, we briefly discuss fine-tuning problems related to this model.

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arXiv2025

Dynamical Dark Energy in light of DESI BAO and Full-Shape Data

Recently, the DESI BAO data has reported a preference of dynamical dark energy (DDE) over the \LambdaCDM cosmology. Apart from the BAO data, the DDE model should be also sensitive to low-redshift measurements of the matter power spectrum data. In this study, we address this point by combining the DESI Y1 data about the matter power spectrum, extracted from the DESI Full-Shape data, with the DESI DR2 BAO data among other probes. After building the DESI Y1 likelihood, we carry out a Markov Chain Monte Carlo analysis, showing that the constraints on $w_0$ and $w_a$ with DESI Y1 data included are improved over those without it for three different datasets widely considered, especially in the case of the DESY5 sample.

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arXiv2025

Illuminating sequential freeze-in dark matter with dark photon signal at the CERN SHiP experiment

Single-field freeze-in dark matter barely leaves observable footprints in dark matter direct detection, collider or fixed-target experiments, which can be altered in the two-field context. In this work, we consider sequential freeze-in dark matter through signals of dark photon mediator with a mass range of $m_{A'}\sim 10^{-2}-10$ GeV covered by the proposed SHiP experiment. We show that the dark charge is fixed to be $e'\sim 1.3\times 10^{-12}$ and the mixing parameter is restricted to $10^{-11}\leq ε< 10^{-8}-10^{-7.5}$, as a result of the out-of-equilibrium condition of dark photon and the observed relic abundance of dark matter. Within this $ε$ region, the 5(15)-year data of proton bremsstrahlung process for the dark photon, assuming vector meson (dipole) dominance, excludes $ε\geq 10^{-8.5} (10^{-7.9})$ at 90\% confidence level, implying only a narrow region of $ε$ close to $\sim 10^{-11}$ left for alternative tests.

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arXiv2025

LHC-friendly freeze-in dark matter via Higgs portal

It is known that single-field freeze-in dark matter barely leaves footprints in dark matter direct detection and collider experiments. This situation can be altered in two-field context. In this work we propose a two-field freeze-in dark matter model through Higgs portal. The observed dark matter relic abundance is obtained by a decay of scalar mediator thermalized in the early Universe. While there is a lack of direct dark matter signals, the scalar mediator is in the reach of HL-LHC either through vector boson fusion or Mono-Z channel. Within allowed scalar mass window of 10-50 GeV, we use improved cuts to derive both $2σ$ exclusion and $5σ$ discovery limits, depending on the value of Higgs portal coupling. If verified, this scalar mediator signal allows us to infer the freeze-in dark matter.

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arXiv2025

Interpreting the Hubble tension with a cascade decaying dark matter sector

Hubble tension can be alleviated by altering either early- or late-time $\Lambda$CDM. With only one of these effects introduced, early dark energy remains the only solution capable of reducing the tension to the $3\sigma$ level or below. In this work, we instead consider a modification of the dark matter sector that incorporates both the early- and late-time effects, with the goal of achieving the largest possible value of $H_0$ within this framework. As a realization of these two-fold effects, we study a cascade decaying dark matter model. By fitting the model to the latest datasets of Planck CMB+ DESI BAO+Pantheon (+SH0ES), we find that a 68$\%$ CL value of $H_{0}=68.76\pm0.35 (69.05^{+0.31}_{-0.27})$ km s$^{-1}$ Mpc$^{-1}$ with $\Delta \rm{AIC}=+22.0(18.4)$, and larger value of $H_0$ can be obtained by adjusting parameter priors but with a cost of significantly increased value of $\Delta \rm{AIC}$. These findings revise the earlier results on the tension level in the literature. For completeness, we show that the parameter regions favored by the cosmological datasets are compatible with complementary limits arising from the Big Bang Nucleosynthesis, neutrino flux, and structure formation.

astro-ph.CO↗

arXiv2024

Constraints on freeze-in dark matter from Lyman-$α$ forest and 21-cm signal : single-field models

We report new Lyman-$α$ and 21-cm constraints on freeze-in dark matter (FIDM) which injects energy into the intergalactic medium either through annihilation or decay to photon(s) or electron-positron pair. With respect to Lyman-$α$ we fix the baseline ionization history using low redshift data about astrophysical reionization, whereas for 21-cm signal we adopt the baseline values of 21-cm power spectrum through a standard modeling of star formation developed so far. Using the latest numerical tools, we show that (i) for sterile neutrino FIDM, current Lyman-$α$ data and future sensitivity of SKA-low (1000 hrs) on the 21-cm power spectra excludes the FIDM mass up to $1.8\times 10^{-3}$ GeV at 95$\%$ CL and $5.46\times 10^{-4}$ GeV, respectively, and (ii) for millicharged FIDM, current Lyman-$α$ data only excludes the millicharge down to $10^{-8}$ within the FIDM mass range of $10^{-3}-1$ GeV at 95$\%$ CL, suggesting that the surviving parameter space of millicharged FIDM is still intact.

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arXiv2024

Self-interacting dark matter to freeze-in via vector portal

It is challenging to resolve the small-scale problem for dark matter being a weakly-interacting massive particle. We attempt to address this issue by proposing a self-interacting freeze-in dark matter via dark photon. In this model, the dark matter obtains the observed relic abundance via Standard Model $γ$ and $Z$ boson induced freeze-in processes, whereas the dark matter force mediator has a negligible relic abundance and a lifetime larger than the age of Universe. We place constraints in classical and resonant regime resolving the small-scale problem from CMB, $X/γ$-ray, Supernova 1987A and out-of-equilibrium condition. It turns out that the CMB constraint on dark matter annihilations is satisfied despite large Sommerfeld effect taking place, while the other constraints are trivially accommodated due to various millicharge induced suppressions. Finally we briefly discuss future cosmological tests on such freeze-in dark matter model.

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arXiv2024

Lyman-$α$ limit on axion-like cold dark matter

Using low redshift data on astrophysical reionization, we report new Lyman-$α$ limit on axion-like particle (ALP) as cold dark matter in ALP mass range of $m_{a}\sim 30-1000$ eV. Compared to the Leo T and soft-X ray bound, this limit is so far the most stringent in the ALP mass range of $m_{a}\sim 375-425$ eV and complementary in the ALP mass range otherwise. Combing these limits, we show new exclusion limits on $m_a$ for the ALP DM from either misalignment or freeze-in mechanism.

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arXiv2024

Gravitational Wave Probe of Gravitational Dark Matter from Preheating

We forecast high-frequency gravitational wave (GW) from preheating hosting gravitational dark matter (GDM) as the indirect probe of such GDM. We use proper lattice simulations to handle resonance, and to solve GW equation of motion with the resonance induced scalar field excitations as source term. Our numerical results show that Higgs scalar excitations in Higgs preheating model give rise to magnitudes of GW energy density spectra of order $10^{-10}$ at frequencies $10-10^{3}$ MHz depending on the GDM mass, whereas inflaton fluctuation excitations in inflaton self-resonant preheating model yield magnitudes of GW energy density spectrum up to $10^{-9}~(10^{-11})$ at frequencies near $30~(2)$ MHz for the index $n=4~(6)$ with respect to the GDM mass of $1.04~(2.66)\times 10^{14}$ GeV.

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arXiv2023

Gravitational freeze-in dark matter from Higgs Preheating

Gravitational freeze-in is a mechanism to explain the observed dark matter relic density if dark matter neither couples to inflation nor to standard model sector. In this work, we study gravitational freeze-in dark matter production during Higgs preheating based on non-perturbative resonance. Using reliable lattice method to handle this non-perturbative process, we show that tachyonic resonance is prohibited by strong back reaction due to Higgs self interaction needed to keep the positivity of potential during preheating, and parameter resonance is viable by tuning the Higgs self-interaction coupling to be small enough in ultraviolet energy scale. We then derive the dark matter relic density under the context of Higgs preheating, and uncover a new dark matter parameter space with dark matter mass larger than inflaton mass, which arises from out-of-equilium Higgs annihilation. Finally, we briefly remark the open question of testing gravitational dark matter.

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arXiv2023

Gravitational Dark Matter from Minimal Preheating

Following our previous work, we continue to explore gravitational dark matter production during the minimal preheating caused by inflaton self-resonance. In this situation there is only one dimensionless index parameter $n$ characterizing the inflation potential after the end of inflation, which leads to a robust prediction on the gravitational dark matter relic abundance. Using lattice method to handle the non-perturbative evolutions of relevant quantities during the inflaton self-resonance, we derive the gravitational dark matter relic abundance arising from both the inflaton condensate and fluctuation annihilation. While being absent for $n=2$, the former one can instead dominate over the later one for $n=4,6$. Our results show that gravitational dark matter mass of $1.04~(2.66)\times 10^{14}$ GeV accommodates the observed value of dark matter relic abundance for $n=4$ (6).

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arXiv2023

Freeze-in Dark Matter via Lepton Portal: Hubble Tension and Stellar Cooling

We propose a new freeze-in dark matter candidate which feebly couples to the standard model charged leptons. The feeble interactions allow it (i) to freeze-in from the Standard Model thermal bath with its relic density being either a fraction or the entirety of the observed dark matter density and (ii) to radiatively decay to two photons in the dark matter mass ranges of order keV scale with lifetime larger than the age of Universe. These features make this model a realistic realization of dark matter with late-time decay to reduce Hubble tension. We show the best-fit value of H_{0}=68.31(69.34) km s^{-1}Mpc^{-1} in light of Planck 2018+BAO(+LSS)+Pantheon data sets. We then use stellar cooling data to place constraints on the parameter space favored by the Hubble tension. While the universal coupling scenario is excluded, the hierarchical coupling scenario can be tested by future observations of white dwarfs after a careful look into photon inverse decay, Primakoff and Bremsstrahlung emission of the dark matter in various stellar systems. The viable parameter space may be linked to anomalies in future X-ray telescopes.

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arXiv2023

Freeze-in dark matter in EDGES 21-cm signal

The first measurement on temperature of hydrogen 21-cm signal reported by EDGES strongly favors Coulomb-like interaction between freeze-in dark matter and baryon fluid. We investigate such dark matter both in one- and two-component context, with the light force carrier(s) essential for the Coulomb-like interaction not being photon. Using a conversion of cross sections used by relevant experiments and Boltzmann equations to encode effects of the dark matter-baryon interaction, we show that both cases are robustly excluded by the stringent stellar cooling bounds in the sub-GeV dark matter mass range. The exclusion of one-component case applies to simplified freeze-in dark matter with the light force carrier as dark photon, gauged $B-L$, $L_{e}-L_μ$,$L_{e}-L_τ$ or axion-like particle, while the exclusion of two-component case applies to simplified freeze-in dark matter with the two light force carriers as two axion-like particles coupled to standard model quarks and leptons respectively.

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arXiv2022

Identifying Minimal Composite Dark Matter

We attempt to identify the minimal composite scalar dark matter from strong dynamics with the characteristic mass of order TeV scale. We provide both direct and indirect limits from dark matter direct detections and collider facilities. Compared to a fundamental scalar dark matter, our results show that in the composite scalar dark matter the disappearing resonant mass region, the smaller spin-independent dark matter-nucleon scattering cross section in certain mass region, and the absence at the HL-LHC illustrate how to differentiate these two dark matter models.

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arXiv2022

Resolving Muon g-2 Anomaly With Partial Compositeness

We consider the scenario of composite Higgs with partial compositeness to address the muon g-2 anomaly. We show that this anomaly is resolved by one-loop correction due to composite muon partners with mass scale of order TeVs and large Yukawa coupling to composite Higgs, which is different from interpretations of vectorlike lepton models. We present parameter space by imposing indirect constraints from precise measurements on Higgs, Z and oblique electroweak parameters. We analyze direct constraints in light of both Drell-Yan and Higgs-associated productions of the composite muon partners at high-luminosity LHC. It turns out that the surviving parameter regions with the lighter composite muon mass below $\sim 325$ GeV can be excluded at 2$σ$ order by the Drell-Yan processes.

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arXiv2022

Complex Field Inflation

We report first study of complex field inflation. Although understood as a specific two-field inflation, a complex field inflation is able to make more robust model predictions on primordial curvature perturbation. Explicitly we discuss the model realizations of complex chaotic and exponential inflation in various large-field contexts. Both complex field models contain a single complex scalar together with only two free parameters. Using numerical handles aimed to calculate primordial curvature perturbation from multifield inflation, we show that both models are compatible with current Planck data, and the individual surviving parameter space can be substantially or fully probed by future CMB-S4 experiments.

astro-ph.CO↗

arXiv2022

R-Symmetric NMSSM

It is well known that the observed Higgs mass is more naturally explained in the NMSSM than in the MSSM. Without any violation of this success, there are variants on the NMSSM which can lead to new phenomenologies. In this study we propose a new variant of NMSSM by imposing an unbroken $R$ symmetry. We firstly identify the minimal structure of such scenario from the perspective of both simplicity and viability, then compare model predictions to current experimental limits, and finally highlight main features that differ from the well-known scenarios.

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arXiv2021

Resolving XENON Excess With Decaying Cold Dark Matter

We propose a decaying cold dark matter model to explain the excess of electron recoil observed at the XENON1T experiment. In this scenario, the daughter dark matter from the parent dark matter decay easily obtains velocity large enough to saturate the peak of the electron recoil energy around 2.5 keV, and the observed signal rate can be fulfilled by the parent dark matter with a mass of order 10-200 MeV and a lifetime larger than the age of Universe. We verify that this model is consistent with experimental limits from dark matter detections, Cosmic Microwave Background and Large Scale Structure experiments.

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