分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: We discuss a class of matrix models describing cosmology with a light-like singularity, generalizing the model proposed by Craps et al. in hep-th/0506180.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: We study a class of models in which the inflaton is minimally coupled to gravity with a term f(R)phiv2. We focus in particular on the case where f~R2, and the expansion of the scale factor is driven by the usual potential energy, while the rolling of the inflaton is driven by the non-minimal coupling. We show that the power spectrum is in general blue, and the problem of getting a running spectral index is eased. However, the inflaton potential must have a large second derivative in order to get a large running.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: We study the structure of the phase space in Horava-Lifshitz theory. With the constraints derived from the action, the phase space is described by five fields, thus there is a lack of canonical structure. The Poisson brackets of the Hamiltonian density do not form a closed structure, resulting in many new constraints. Taking these new constraints into account, it appears that there is no degree of freedom left, or the phase space is reduced to one with an odd number of fields.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: We propose to embed de Sitter space into five dimensional anti-de Sitter space to compute some physical quantities of interest, using the AdS/CFT correspondence. The static de Sitter can be considered as the conformal structure of the boundary of the hyperbolic AdS(5) with a horizon, thus energy as well as entropy can be computed. The global dS can be embedded into a half-global AdS(5), and the dS entropy can be regarded as entanglement entropy in this case. Finally, the inflationary dS can also be regarded as the boundary of AdS(5), and this can be extended to include general cosmology with a positive cosmological constant, however at the price of introducing a naked null singularity in the bulk unless the cosmology is pure de Sitter space.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: We investigate the measure problem in the framework of inflationary cosmology. The measure of the history space is constructed and applied to inflationmodels. Using this measure, it is shown that the probability for the generalized single-field slow roll inflation to last for N e-folds is suppressed by a factor exp(-3N), and the probability for the generalized n-field slow roll inflation is suppressed by a much larger factor, exp(-3nN). Some non-inflationary models such as the cyclic model do not suffer from this difficulty.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: We use the stochastic approach to investigate a measure for slow roll eternal inflation. The probability for the universe to have a given Hubble radius can be calculated in this framework. In a solvable model, it is shown that the probability for the universe to evolve from a state with a smaller Hubble radius to one with a larger Hubble radius is dominated by the classical probability without the stochastic source, while the probability for the universe to evolve from a state with a larger Hubble radius to one with a smaller one is suppressed by exp(-Delta S), where the de Sitter entropy S arises naturally in this stochasticapproach.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: We propose a model in which an energy-dependent time delay of a photon originates from space-time non-commutativity, the time delay is due to a non-commutative coupling between dilaton and photon. We predict that in our model, high energy photons with different momentum can either be delayed or superluminal, this may be related to a possible time delay reported by the Fermi LAT and Fermi GBM Collaborations
分类: 天文学 >> 星系和宇宙学 提交时间: 2023-02-21
摘要: Interstellar (ISM) and circumgalactic medium (CGM) around galaxies are linked to several physical processes that drive galaxy evolution. For example, the X-ray emission from the CGM gas around ellipticals has been linked to the AGN feedback occurring in the host. Upcoming telescopes such as HUBS, with ~ 1 eV resolution, can provide us with deep insights about the hot gas properties of such galaxies thus constrain these processes. In this project, we discuss X-ray emission of the ISM and CGM of elliptical galaxies simulated using MACER code. We generate X-ray emission data from the MACER simulations with various feedback models and produce mock observations for an instrument with high spectral resolution, which is a necessary step of selecting sources for the future observations with planned mission such as HUBS. More importantly, we establish connections between the physics of AGN and stellar feedback with the emission spectra from the ISM and CGM to investigate the possibility of using observations to constrain feedback models. We fit the X-ray spectra from these simulations with standard fitting procedures and compare the retrieved physical properties with their counterparts from the simulations to understand whether the future high-resolution observations can reliably reveal the properties of the gas in the galaxies.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: In this paper we investigate the possible direct, non-gravitational interaction between holographic dark energy (HDE) and dark matter. Firstly, we start with two simple models with the interaction terms Q proportional to rho(dm) and Q proportional to rho(de), and then we move on to the general form Q proportional to rho(alpha)(m)rho(beta)(de). The cosmological constraints of the models are obtained from the joint analysis of the present Union 2.1+BAO+CMB+H-0 data. We find that the data slightly favor an energy flow from dark matter to dark energy, although the original HDE model still lies in the 95.4% confidence level (CL) region. For all models we find c -1. We show that this solution cannot be accomplished in the two simple models, while for the general model such a solution can be achieved with a large beta, and the big rip may be avoided at the 95.4% CL.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Interstellar (ISM) and circumgalactic medium (CGM) around galaxies are linked to several physical processes that drive galaxy evolution. For example, the X-ray emission from the CGM gas around ellipticals has been linked to the AGN feedback occurring in the host. Upcoming telescopes such as HUBS, with ~ 1 eV resolution, can provide us with deep insights about the hot gas properties of such galaxies thus constrain these processes. In this project, we discuss X-ray emission of the ISM and CGM of elliptical galaxies simulated using MACER code. We generate X-ray emission data from the MACER simulations with various feedback models and produce mock observations for an instrument with high spectral resolution, which is a necessary step of selecting sources for the future observations with planned mission such as HUBS. More importantly, we establish connections between the physics of AGN and stellar feedback with the emission spectra from the ISM and CGM to investigate the possibility of using observations to constrain feedback models. We fit the X-ray spectra from these simulations with standard fitting procedures and compare the retrieved physical properties with their counterparts from the simulations to understand whether the future high-resolution observations can reliably reveal the properties of the gas in the galaxies.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: When a gravitational wave or a graviton travels through an electric or magnetic background, it could convert into a photon with some probability. In this paper, a dipole magnetic field is considered as this kind of background in both the Minkowski spacetime and the curved spacetime in the near-zone of a neutron star. In the former case, we find that the graviton traveling vertically rather than parallel to the background magnetic field could be more effectively converted into an electromagnetic radiation field. In the latter case, we focus on the situation, in which the graviton travels along the radial direction near a neutron star. The radius of a neutron star is about ten kilometers, so the gravitational wave with long wavelength or low frequency may bypass neutron stars by diffraction. For high frequency gravitational wave, the conversion probability is proportional to the distance square as that in the static electric or magnetic background case. The smaller the inclination angle between the dipole field and the neutron star north pole is, the larger magnetic amplitude will be. The term that described curved spacetime will slightly enhance this kind of probability. We estimate that this value is about the order of $\sim 10^{-14}- 10^{-10}$. Therefore, it is expectable that this kind of conversion process may have a potential to open a window for observing high frequency gravitational waves.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We compare 500~pc scale, resolved observations of ionised and molecular gas for the $z\sim0.02$ starbursting disk galaxy IRAS08339+6517, using measurements from KCWI and NOEMA. We explore the relationship of the star formation driven ionised gas outflows with colocated galaxy properties. We find a roughly linear relationship between the outflow mass flux ($\dot{\Sigma}_{\rm out}$) and star formation rate surface density ($\Sigma_{\rm SFR}$), $\dot{\Sigma}_{\rm out}\propto\Sigma_{\rm SFR}^{1.06\pm0.10}$, and a strong correlation between $\dot{\Sigma}_{\rm out}$ and the gas depletion time, such that $\dot{\Sigma}_{\rm out} \propto t_{dep}^{-1.1\pm0.06}$. Moreover, we find these outflows are so-called ``breakout" outflows, according to the relationship between the gas fraction and disk kinematics. Assuming that ionised outflow mass scales with total outflow mass, our observations suggest that the regions of highest $\Sigma_{\rm SFR}$ in IRAS08 are removing more gas via the outflow than through the conversion of gas into stars. Our results are consistent with a picture in which the outflow limits the ability for a region of a disk to maintain short depletion times. Our results underline the need for resolved observations of outflows in more galaxies.