分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We quantitatively study how the primordial density fluctuations are imprinted on the anisotropy of the phase transition gravitational wave (PTGW). Generated long before recombination and free from Silk damping, the anisotropic PTGW might reveal the density perturbation seeded from inflation or alternatives. We find new behaviors of the PTGW anisotropy power spectrum. The PTGW anisotropy is stronger than the anisotropy of the cosmic microwave background temperature at all scales, and the high-$\ell$ multiples are enhanced about 1 order due to the early integrated Sachs-Wolfe effect. Furthermore, differences in primordial power spectra at small scales manifest themselves more significantly on the angular power spectrum of PTGW anisotropy compared to that of the cosmic microwave background. These properties might provide a novel clue to understanding the primordial density perturbation of our early Universe and thereby complete our understanding of inflation theory. Taking nanohertz PTGW from dark matter models as a typical example, we obtain amplitudes of PTGW anisotropy which are about 4 or 3 orders weaker than the isotropic PTGW energy spectra.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: AliCPT-1 is the first Chinese CMB experiment aiming for high precision
measurement of Cosmic Microwave Background B-mode polarization. The telescope,
currently under deployment in Tibet, will observe in two frequency bands
centered at 90 and 150 GHz. We forecast the CMB lensing reconstruction,
lensing-galaxy as well as lensing-CIB (Cosmic Infrared Background) cross
correlation signal-to-noise ratio (SNR) for AliCPT-1. We consider two stages
with different integrated observation time, namely "4 module*yr" (first stage)
and "48 module*yr" (final stage). For lensing reconstruction, we use three
different quadratic estimators, namely temperature-only, polarization-only and
minimum-variance estimators, using curved sky geometry. We take into account
the impact of inhomogeneous hit counts as well as of the mean-field bias due to
incomplete sky coverage. In the first stage, our results show that the 150 GHz
channel is able to measure the lensing signal at $15\sigma$ significance with
the minimum-variance estimator. In the final stage, the measurement
significance will increase to $31\sigma$. We also combine the two frequency
data in the harmonic domain to optimize the SNR. Our result show that the
coadding procedure can significantly reduce the reconstruction bias in the
multiple range l>800. Thanks to the high quality of the polarization data in
the final stage of AliCPT-1, the EB estimator will dominate the lensing
reconstruction in this stage. We also estimate the SNR of cross-correlations
between AliCPT-1 CMB lensing and other tracers of the large scale structure of
the universe. For its cross-correlation with DESI galaxies/quasars, we report
the cross-correlation SNR = 10-20 for the 4 redshift bins at 0.05
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: AliCPT is the first Chinese cosmic microwave background (CMB) experiment which will make the most precise measurements of the CMB polarization in the northern hemisphere. The key science goal for AliCPT is the detection of primordial gravitational waves (PGWs). It is well known that an epoch of cosmic inflation, in the very early universe, can produce PGWs, which leave an imprint on the CMB in form of odd parity $B$-mode polarization. In this work, we study the performance of the component separation and parameter estimation pipelines in context of constraining the value of the tensor-to-scalar ratio. Based on the simulated data for one observation season, we compare five different pipelines with different working principles. Three pipelines perform component separation at map or spectra level before estimating $r$ from the cleaned spectra, while the other two pipelines performs a global fit for both foreground parameters and $r$. We also test different methods to account for the effects of time stream filtering systematics. This work shows that our pipelines provide consistent and robust constraints on the tensor-to-scalar ratio and a consistent sensitivity $\sigma(r) \sim 0.02$. This showcases the potential of precise $B$-mode polarization measurement with AliCPT-1. AliCPT will provide a powerful opportunity to detect PGWs, which is complementary with various ground-based CMB experiments in the southern hemisphere.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Cosmic microwave background radiation (CMB) observations are unavoidably contaminated by emission from various extra-galactic foregrounds, which must be removed to obtain reliable measurements of the cosmological signal. In this paper, we demonstrate CMB lensing reconstruction in AliCPT-1 after foreground removal, combine the two bands of AliCPT-1 (90 and 150~GHz) with Planck HFI bands (100, 143, 217 and 353~GHz) and with the WMAP-K band (23~GHz). In order to balance contamination by instrumental noise and foreground residual bias, we adopt the Needlet Internal Linear Combination (NILC) method to clean the E-map and the constrained Internal Linear Combination (cILC) method to clean the B-map. The latter utilizes additional constraints on average frequency scaling of the dust and synchrotron to remove foregrounds at the expense of somewhat noisier maps. Assuming 4 modules observing 1 season from simulation data, the resulting effective residual noise in E- and B-map are roughly $15~\mu{\rm K}\cdot{\rm arcmin}$ and $25~\mu{\rm K}\cdot{\rm arcmin}$, respectively. As a result, the CMB lensing reconstruction signal-to-noise ratio (SNR) from polarization data is about SNR$\,\approx\,$4.5. This lensing reconstruction capability is comparable to that of other stage-III small aperture millimeter CMB telescopes.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Cosmic microwave background radiation (CMB) observations are unavoidably contaminated by emission from various extra-galactic foregrounds, which must be removed to obtain reliable measurements of the cosmological signal. In this paper, we demonstrate CMB lensing reconstruction in AliCPT-1 after foreground removal, combine the two bands of AliCPT-1 (90 and 150~GHz) with Planck HFI bands (100, 143, 217 and 353~GHz) and with the WMAP-K band (23~GHz). In order to balance contamination by instrumental noise and foreground residual bias, we adopt the Needlet Internal Linear Combination (NILC) method to clean the E-map and the constrained Internal Linear Combination (cILC) method to clean the B-map. The latter utilizes additional constraints on average frequency scaling of the dust and synchrotron to remove foregrounds at the expense of somewhat noisier maps. Assuming 4 modules observing 1 season from simulation data, the resulting effective residual noise in E- and B-map are roughly $15~\mu{\rm K}\cdot{\rm arcmin}$ and $25~\mu{\rm K}\cdot{\rm arcmin}$, respectively. As a result, the CMB lensing reconstruction signal-to-noise ratio (SNR) from polarization data is about SNR$\,\approx\,$4.5. This lensing reconstruction capability is comparable to that of other stage-III small aperture millimeter CMB telescopes.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The energy budget of cosmological first-order phase transition is essential for the gravitational wave spectra. Most of the previous studies are based on the bag model with same sound velocity in the symmetric and broken phase. We study the energy budget and the corresponding gravitational wave spectra beyond the bag model, where the sound velocities could be different in the symmetric and broken phase. Taking the Higgs sextic effective model as a representative model, we calculate the sound velocities in different phase, the gravitational wave spectra and the signal-to-noise ratio for different combinations of phase transition parameters beyond the bag model. We compare these new results with the ones obtained from the bag model.The proper sound velocities and phase transition parameters at the appropriate temperature are important to obtain more precise predictions.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
摘要: In this paper, we will give a general introduction to the project of Ali CMB Polarization Tele-scope (AliCPT), which is a Sino-US joint project led by the Institute of High Energy Physics (IHEP) and has involved many di erent institutes in China. It is the rst ground-based cosmic microwave background (CMB) polarization experiment in China and an integral part of China's Gravitational Waves Program. The main scienti c goal of AliCPT project is to probe the primor-dial gravitational waves (PGWs) originated from the very early Universe. The AliCPT project includes two stages. The rst stage referred to as AliCPT-1, is to build a telescope in the Ali region of Tibet with an altitude of 5,250 meters. Once completed, it will be the worldwide highest ground-based CMB observatory and open a new window for probing PGWs in northern hemisphere. AliCPT-1 telescope is designed to have about 7,000 TES detectors at 90GHz and 150GHz. The second stage is to have a more sensitive telescope (AliCPT-2) with the number of detectors more than 20,000. Our simulations show that AliCPT will improve the current constraint on the tensor-to-scalar ratio r by one order of magnitude with 3 years' observation. Besides the PGWs, the AliCPT will also enable a precise measurement on the CMB rotation angle and provide a precise test on the CPT symmetry. We show 3 years' observation will improve the current limit by two order of magnitude.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
摘要: Motivated by the discovery of gravitational waves (GWs) at aLIGO and no evidence of new physics at current LHC, we discuss that a generic classes of extended new physics models with hidden gauge group could undergo one or several times rst-order phase transitions associated with the gauge group symmetry breaking during the evolution of the universe, which might produce detectable phase transition GWs signals at future GWs experiments, such as eLISA and BBO.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: The w−w′ plane, defined by the equation of state parameter for the dark energy and its derivative with respect to the logarithm of the scale factor, is useful to the study of classifying the dynamical dark energy models. In this note, we examine the evolving behavior of the two-field quintom models with w crossing the w = −1 barrier in the w − w′ plane. We find that these models can be divided into two categories, type A quintom in which w changes from > −1 to −1 as the universe expands.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We investigate in this paper the cosmological evolution of a dark energy model with two scalar fields where one of the scalar has canonical kinetic energy and another scalar has negative kinetic energy term. For such a system with exponential potentials we find that during the evolution of the universe the equation of state w changes from w > −1 to w < −1, which is consistent with the recent observations. A phase-plane analysis shows that the “phantom”-dominated scaling solution is the stable late-time attractor of this type of models.
分类: 物理学 >> 核物理学 提交时间: 2016-09-19
摘要: The study of reionization history plays an important role in understanding the evolution of our universe. It is commonly believed that the intergalactic medium (IGM) in our universe are fully ionized today, however the reionizing process remains to be mysterious. A simple instantaneous reionization process is usually adopted in modern cosmology without direct observational evidence. However, the history of ionization fraction, xe(z) will influence cosmic microwave background (CMB) observables and constraints on optical depth τ. With the mocked future data sets based on featured reionization model, we find the bias on τ introduced by instantaneous model can not be neglected. In this paper, we study the cosmic reionization history in a model independent way, the so called principle component analysis (PCA) method, and reconstruct xe(z) at different redshift z with the data sets of Planck, WMAP 9 years temperature and polarization power spectra, combining with the baryon acoustic oscillation (BAO) from galaxy survey and type Ia supernovae (SN) Union 2.1 sample respectively. The results show that reconstructed xe(z) is consistent with instantaneous behavior, however, there exists slight deviation from this behavior at some epoch. With PCA method, after abandoning the noisy modes, we get stronger constraints, and the hints for featured xe(z) evolution could become a little more obvious.
分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: We study the collider phenomenology of the electroweak phase transition and electroweak baryogenesis in the framework of the effective field theory. Our study shows that the effective theory using the dimension-6 operators can enforce strong first order phase transition and provide sizable CP violation to realize a successful electroweak baryogenesis. Such dimension-6 operators can induce interesting Higgs phenomenology that can be verified at colliders such as the LHC and the planning CEPC. We then demonstrate that this effective theory can originate from vector-like quarks and the triplet Higgs.
分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: It is of great interest to connect cosmology in the early universe to the Standard Model of particle physics. In this paper, we try to construct a bounce inflation model with the standard model Higgs boson, where the one loop correction is taken into account in the effective potential of Higgs field. In this model, a Galileon term has been introduced to eliminate the ghost mode when bounce happens. Moreover, due to the fact that the Fermion loop correction can make part of the Higgs potential negative, one naturally obtains a large equation of state(EoS) parameter in the contracting phase, which can eliminate the anisotropy problem. After the bounce, the model can drive the universe into the standard higgs inflation phase, which can generate nearly scale-invariant power spectrum.
分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: The observed value of the Higgs mass indicates an instability of the Higgs scalar at large energy scales, and hence also at large field values. In the context of early universe cosmology, this is often considered to lead to problems. Here we point out that we can use the instability of the Higgs field to generate an Ekpyrotic phase of contraction. In the context of string theory it is possible that at very high energy densities extra states become massless, leading to an S-brane which leads to the transition between a contracting phase in the past and the current expanding phase. Thus, the Higgs field can be used to generate a non-singular bouncing cosmology in which the anisotropy problem of usual bouncing scenarios is mitigated.
分类: 物理学 >> 核物理学 提交时间: 2016-09-13
摘要: At upcoming medium baseline reactor neutrino experiments the spallation 9Li background will be somewhat larger than the inverse beta decay reactor neutrino signal. We use new FLUKA simulations of spallation backgrounds to optimize a class of veto strategies and find that surprisingly the optimal veto for the mass hierarchy determination has a rejection efficiency below 90%. The unrejected background has only a modest effect on the physics goals. For example Δχ2 for the hierarchy determination falls by 1.4 to 3 points depending on the muon tracking ability. The optimal veto strategy is essentially insensitive to the tracking ability, consisting of 2 meter radius, 1.1 second cylindrical vetoes of well tracked muons with showering energies above 3 to 4 GeV and 0.7 second full detector vetoes for poorly tracked muons above 15 to 18 GeV. On the other hand, as the uncertainty in theta12 will be dominated by the uncertainty in the reactor neutrino spectrum and not statistical fluctuations, the optimal rejection efficiency for the measurement of theta12 is 93% in the case of perfect tracking.
分类: 物理学 >> 核物理学 提交时间: 2016-09-13
摘要: The recently discovered 5 MeV bump highlights that the uncertainty in the reactor neutrino spectrum is far greater than some theoretical estimates. Medium baseline reactor neutrino experiments will deliver by far the most precise ever measurements of theta12. However, as a result of the bump, such a determination of theta12 using the theoretical spectrum would yield a value of sin^2(2theta12) which is more than 1% higher than the true value. We show that by using recent measurements of the reactor neutrino spectrum the precision of a measurement of theta12 at a medium baseline reactor neutrino experiment can be improved appreciably. We estimate this precision as a function of the 9Li spallation background veto efficiency and dead time.
分类: 物理学 >> 核物理学 提交时间: 2016-09-05
摘要: Recently, a novel idea has been proposed to relax the electroweak hierarchy problem through the cosmological inflation and the axion periotic potential. Here, we further assume that only attractive inflation is needed to explain the light mass of the Higgs boson, where we do not need specified periotic potential of the axion field. Attractive inflation during the early universe drives the Higgs boson mass from the large value in the early universe to the small value at present, and the small Higgs mass can technically origin from the cosmological evolution rather than dynamical symmetry or antropics, where the Higgs mass is an evolving parameter of the Universe. Further, we study the possible collider signals or constraints at future lepton collier and the possible constraints from the muon anomalous magnetic moment. A concrete attractive relaxion model is also discussed, which is consistent with the data of Planck 2015.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: In this letter, we explore the nature of the electroweak phase transition (EWPT) with both particle colliders and gravitational wave (GW) detection. With the observed Higgs mass, the shape of the Higgs potential is fully determined within the standard model (SM) of particle physics. However, it could be changed if there exists new physics beyond the SM. Working with the effective field theory, we show that a modified Higgs potential with a sextic term included can keep the observed 125 GeV Higgs mass but behave different when compared with the SM case. Furthermore, this potential can produce a strong first order phase transition (SFOPT) for the electroweak baryogenesis and interestingly predict new phenomena in the Higgs sector, which can be tested at colliders such as the Large Hadron Collider (LHC) and the planning Circular Electron Positron Collider (CEPC). We point out this SFOPT can lead to detectable signals for the GW interferometers , such as eLISA, DECIGO and BBO. Our present study on the EWPT bridges the particle physics at colliders with the astrophysics and cosmology in the early universe.