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Probing Primordial Gravitational Waves: Ali CMB Polarization Telescope

Hong Li; Si-Yu Li; Yang Liu; Yong-Ping Li; Yifu Cai; Mingzhe Li; Gong-Bo Zhao; Cong-Zhan Liu; Zheng-Wei Li; He Xu; Di Wu; Yong-Jie Zhang; Zu-Hui Fan; Yong-Qiang Yao; Chao-Lin Kuo; Fang-Jun Lu; Xinmin ZhangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

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. |

submitted time
2017-11-10
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Probing the hidden gauge symmetry breaking through the phase transition gravitational waves

Fa Peng Huang; Xinmin ZhangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

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. |

Two-Field Quintom Models in the w ? w Plane

Zong-Kuan Guo; Yun-Song Piao; Xinmin Zhang; Yuan-Zhong ZhangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

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 and type B quintom in which w changes from < ?1 to > ?1 as the universe expands. |

submitted time
2017-09-27
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Cosmological Evolution of a Quintom Model of Dark Energy

Zong-Kuan Guo; Yun-Song Piao; Xinmin Zhang; Yuan-Zhong ZhangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

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. |

submitted time
2017-09-27
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Cosmic Reionization Study : Principle Component Analysis After Planck

Yang Liu; Hong Li; Si-Yu Li; Yong-Ping Li; Xinmin ZhangSubjects: Physics >> Nuclear Physics

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. |

Subjects: Physics >> Nuclear Physics

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. |

Bounce Inflation Cosmology with Standard Model Higgs Boson

Youping Wan; Taotao Qiu; Fa Peng Huang; Yi-Fu Cai; Hong Li; Xinmin ZhangSubjects: Physics >> Nuclear Physics

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. |

Nonsingular Cosmology from an Unstable Higgs Field

Robert H. Brandenberger; Yi-Fu Cai; Youping Wan; Xinmin ZhangSubjects: Physics >> Nuclear Physics

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. |

Vetoing Cosmogenic Muons in A Large Liquid Scintillator

Marco Grassi; Jarah Evslin; Emilio Ciuffli; Xinmin ZhangSubjects: Physics >> Nuclear Physics

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. |

Measuring $\theta_12$ despite an uncertain reactor neutrino spectrum

Emilio Ciuffoli; Jarah Evslin; Marco Grassi; Xinmin ZhangSubjects: Physics >> Nuclear Physics

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. |