Observational Constraints on Varying Alpha in Λ(α)CDM Cosmology

In this work, we consider the so-called Λ(α)CDM cosmology with Λ∝α^(-6) while the fine-structure"constant" α is varying. In this scenario, the accelerated expansion of the universe is driven by the cosmological"constant" Λ(equivalently the vacuum energy), and the varying α is driven by a subdominant scalar field ? coupling with the electromagnetic field. The observational constraints on the varying α and Λ∝α^(-6) models with various couplings BF(?) between the subdominant scalar field ? and the electromagnetic field are considered.

Constraints on Dark Energy Models from Weak Gravity Conjecture

We study the constraints on the dark energy model with constant equation of state parameter w = pip and the holographic dark energy model by using the weak gravity conjecture. The combination of weak gravity conjecture and the observational data gives tu 〈 -0.7 at the 3σ confidence level. The holographic dark energy model realized by a scalar field is in swampland.

Regional Boundary Observability with Constraints of the Gradient

The aim of this paper is to explore the concept of observability with constraints of the gradient for distributed parabolic system evolving in spatial domain Ω, and which the state gradient is to be observed only on a part of the boundary of the system evolution domain. It consists in the reconstruction of the initial state gradient which must be between two prescribed functions in a subregion Γ of Ω. Two necessary conditions are given. The first is formulated in terms of the subdifferential associated with a minimized functional, and the second uses the Lagrangian multiplier method. Nu-merical illustrations are given to show the efficiency of the second approach and lead to open questions.

Constraining Neutrino Mass in Dynamical Dark Energy Cosmologies with the Logarithm Parametrization and the Oscillating Parametrization

We constrain two dynamical dark energy models that are parametrized by the logarithm form of and the oscillating form of . Comparing with the Chevallier-Polarski-Linder (CPL) model, the two parametrizations for dark energy can explore the whole evolution history of the universe properly. Using the current mainstream observational data including the cosmic microwave background data and the baryon acoustic oscillation data as well as the type Ia supernovae data, we perform the X2 statistic analysis to global fit these models, finding that the logarithm parametrization and the oscillating parameterization are almost as well as the CPL scenario in fitting these data. We make a comparison for the impacts of the dynamical dark energy on the cosmological constraints on the total mass of active neutrinos. We find that the logarithm parametrization and the oscillating parameterization can increase the fitting values of Σmv. Looser constraints on Σmv are obtained in the logarithm and oscillating models than those derived in the CPL model. Consideration of the possible mass ordering of neutrinos reveals that the most stringent constraint on Σmv appears in the degenerate hierarchy case.

New initial condition of the new agegraphic dark energy model

The initial condition Ωde（zini）=n^2（1＋zini）^-2/4 at zini = 2000,widely used to solve the differential equation of the density of the new agegraphic dark energy（NADE） Ωde,makes the NADE model a single-parameter dark-energy cosmological model.However,we find that this initial condition is only applicable in a flat universe with only dark energy and pressureless matter.In fact,in order to obtain more information from current observational data,such as the cosmic microwave background（CMB） and the baryon acoustic oscillations（BAO）,we need to consider the contribution of radiation.For this situation,the initial condition mentioned above becomes invalid.To overcome this shortcoming,we investigate the evolutions of dark energy in matter-dominated and radiation-dominated epochs,and obtain a new initial condition de（zini）=n2（1＋zini）-2（1＋F（zini））2/4 at z ini = 2000,where F（z）≡Ωr0（1＋z）/[Ωm0＋Ωr0（1＋z）] with Ωr0 and Ωm0 being the current density parameters of radiation and pressureless matter,respectively.This revised initial condition is applicable for the differential equation of Ωde obtained in the standard Friedmann-Robertson-Walker（FRW） universe with dark energy,pressureless matter,radiation,and even spatial curvature,and can still keep the NADE model as a single-parameter model.With the revised initial condition and the observational data of type Ia supernova（SNIa）,CMB,and BAO,we finally constrain the NADE model.The results show that the single free parameter n of the NADE model can be constrained tightly.

Observational insights into the accelerating universe through reconstruction of the deceleration parameter

Recent developments in the exploration of the universe suggest that it is in an accelerated phase of ex-pansion.Accordingly,our study aims to probe the current scenario of the universe with the aid of the reconstruction technique.The primary factor that describes cosmic evolution is the deceleration parameter.Here,we provide a physically plausible,newly defined model-independent parametric form of the deceleration parameter.Further,we constrain the free parameters through statistical MCMC analysis for different datasets,including the most recent Pantheon+.With the statistically obtained results,we analyze the dynamics of the model through the phase trans-ition,EoS parameter,and energy conditions.Also,we make use of the tool Om diagnostic to test our model.

Constraining the f(R,T)=R+2λT cosmological model using recent observational data

In this study,we conduct a comprehensive investigation of the cosmological model described by f(R,T)=R+2λT(whereλrepresents a free parameter)in light of the most recent observational data.By constraining the model using the Hubble and Pantheon datasets,we determine its compatibility with the observed behavior of the Universe.For this purpose,we adopt a parametric form for the effective equation of state(EoS)parameter.This parametric form allows us to describe the evolution of the EoS parameter with respect to redshift and investigate its behavior during different cosmic epochs.The analysis of the deceleration parameter reveals an accelerating Universe with a present value of q0=−0.64_(−0.03)^(+0.03),indicating the current phase of accelerated expansion.The transition redshift is found to be ztr=0.53_(−0.03)^(+0.04),marking the epoch of transition from deceleration to acceleration.We also analyze the evolution of important cosmological parameters,including the density parameter,pressure,effective EoS,and stability.These findings collectively demonstrate the viability of the f(R,T)cosmological model as a robust candidate capable of engendering the requisite negative pressure,thereby efficiently propelling cosmic expansion.Moreover,the undertaken stability analysis underscores the model's stability within the broader cosmic landscape.By providing the best-fit values for the coupling parameterλ,this approach motivates and encourages further exploration into the extensive landscape of this model and its potential applications across diverse realms of cosmology and astronomy.

Projections of summer light rain frequency in typical terrain over eastern China under wind speed constraint

The variation in near-surface wind speed is a key dynamic parameter in the orographic effect of precipitation over eastern China.In this study,we used the latest high-resolution outputs from six GCMs in CMIP6-HighResMIP to evaluate the performance of high-resolution models in simulating the orographic precipitation characteristics of typical mountainous areas in summer over eastern China.The orographic precipitation under warming scenarios was projected and constrained according to observational data.The results indicated that during the contemporary climate reference period(1979-2009),although the relationship between model-simulated near-surface wind speed and orographic light rain frequency was consistently stable,the sensitivity of the orographic light rain frequency to surface wind variability was generally underestimated,with a deviation approximately 24.1% lower than the observational values.The estimated orographic light rain frequency corrected based on the observed near-surface wind speed under a 1.5℃ warming scenario,was 36.1% lower than that of the contemporary period;this reduction was 8.6 times that without the wind speed constraint(4.2%).The MRI-AGCM3-2-S model,with a longer dataset,demonstrated relatively stable reductions in orographic light rain frequency under different warming scenarios(1.5℃,2℃,3℃,and 4℃)after the application of wind speed constraints.In all cases,the reductions exceeded those for the predictions made without the wind speed constraint.

Constrained high-resolution projection of hot extremes in the BeijingeTianjineHebei region of China

The BeijingeTianjineHebei(BTH)region is the political center and one of the largest and most dynamic economic centers in China.Relative to other regions of China,it faces greater challenges from increasing hot extremes.However,future projections of regional changes in hot extremes based on multi-model ensembles carry huge uncertainty.To improve the reliability of regional projections,we used the latest highresolution outputs from nine GCMs in CMIP6-HighResMIP and constrained the projection of hot extremes in this region.In the BTH,the historical scaling of the annual maximum temperature with the mean summer(JuneeAugust)temperatures(TXx scaling)showed a significant linear relationship with the future TXx scaling in the multi-model ensemble.By comparing the observed and simulated historical TXx scaling we identified an observational constraint that could reduce the uncertainty of TXx scaling.We believed that the simulations of EC-Earth3P,ECEarth3P-HR,MPI-ESM1-2-HR and MPI-ESM1-2-XR show advantages in simulating surface air temperature and related hot extremes in this region.Verification demonstrated that surface air temperature projection in the BTH region constrained by observational constraint is more reliable.In constrained projections,by the 2040s,the increase in summer surface air temperatures is projected to exceed 1C compared to 2010s.Also,the estimated number of days of compound(sequential hot day-night)hot extremes(HND),independent hot nights(HNi)and independent hot days(HDi)was found to increase by 0.3,0.3,and-0.03 d per year during 2015-2049,respectively.The growth in numbers of days of HND,HNi and HDi was slower after observational constraint.Furthermore,the estimated increase in surface air temperature variables after constraint also reduced.This study provides support for adaptation policy-making and as a reference for the use of observational constraint in other regions of China.

Probing the sign-changeable interaction between dark energy and dark matter with current observations

We consider the models of vacuum energy interacting with cold dark matter in this study, in which the coupling can change sigh during the cosmological evolution. We parameterize the running coupling b by the form b（a） = boa ＋ be（1 - a）, where at the earlytime the coupling is given by a constant be and today the coupling is described by another constant bo. We explore six specific models with （i） Q = b（a）Hoρo, （ii） Q = b（a）Hoρde, （iii） Q = b（a）Hoρc, （iv） Q = b（a）Hρo, （v） Q = b（a）Hρde, and （vi） Q = b（a）Hρc. The current observational data sets we use to constrain the models include the JLA compilation of type Ia supernova data, the Planck 2015 distance priors data of cosmic microwave background observation, the baryon acoustic oscillations measurements and the Hubble constant direct measurement. We find that, for all the models, we have b0 〈 0 and be 〉 0 at around the lolevel, and b0 and be are in extremely strong anti-correlation. Our results show that the coupling changes sign during the evolution at about the lolevel, i.e., the energy transfer is from dark matter to dark energy when dark matter dominates the universe and the energy transfer is from dark energy to dark matter when dark energy dominates the universe.

Inferring future warming in the Arctic from the observed global warming trend and CMIP6 simulations

The emergent constraint approach is a way of using multi-model ensembles to identify the linkage between current/past climate variability and future climate changes,which has been widely used for narrowing down the uncertainty of multi-model projections of future climate change.Climate models of the latest Coupled Model Intercomparison Project Phase 6(CMIP6)show a much stronger Arctic wanning signal but with a larger inter-model spread.In this study,we find that the projected Arctic warming made by multi-models in CMIP6 is positively correlated with the simulated global warming trend during the period of 1981-2011 in historical runs.This enables us to tighter constraints to future warming in the Arctic by using the observed global warming during the instrument era.The fact that CMIP6 models tend to overestimate the trend of global mean surface temperature during 1981-2011,therefore,would imply a relative weak Arctic warming compared to the CMIP6 median warming projection.