Neutrino masses in astrophysics and cosmology

Cosmology yields the most restrictive limits on neutrino masses and conversely, massive neutrinos would contribute to the cosmic dark-matter density and would play an important role for the formation of structure in the universe. Neutrino oscillations may well solve the solar neutrino problem and can have a significant impact on supernova physics. The neutrino signal from a future galactic supernova could provide evidence for cosmologically interesting neutrino masses or set interesting limits.     

Cosmology with the Nearby Supernova Factory

The Nearby Supernova Factory (SNfactory) is currently finishing its first survey of low redshift (0.03<z<0.08) type Ia supernovae. These data add to the understanding of the expansion history of the universe. Observations are performed using the Supernova Integral Field Spectrograph (SNIFS), an integral field spectrograph delivering full spectro-photometric information of the target. The corresponding dataset aims at the inference of the Hubble diagram zero point with unprecedented accuracy. Moreover, the data offers a variety of related physical studies such as the understanding of progenitor systems, explosion scenarios and host galaxy characteristics. The SNfactory is also working on novel methods accessible with spectro-photometric measurements, reducing systematic uncertainties and improving the statistical power of the SN data.     

Recent Results in Cosmic Ray Physics and Their Interpretation

The last decade has been dense with new developments in the search for the sources of Galactic cosmic rays. Some of these developments have confirmed the tight connection between cosmic rays and supernovae in our Galaxy, through the detection of gamma rays and the observation of thin non-thermal X-ray rims in supernova remnants. Some others, such as the detection of features in the spectra of some chemicals, opened new questions on the propagation of cosmic rays in the Galaxy and on details of the acceleration process. Here, I will summarize some of these developments and their implications for our understanding of the origin of cosmic rays. I will also discuss some new avenues that are being pursued in testing the supernova origin of Galactic cosmic rays.     

Supernovae and cosmology

The extreme luminosity and their fairly unique temporal behaviour have made supernovae a superb tool to measure distances in the universe. As complex astrophysical events they provide interesting insights into explosion physics, explosive nucleosynthesis, hydrodynamics of the explosion and radiation transport. They are an end product of stellar evolution and provide clues to the stellar composition. Since they can be observed at large distances they have become critical probes to further explore astrophysical effects, like dust properties in external galaxies and the star formation history of galaxies. Some of the astrophysics interferes with the cosmological applications of supernovae. The local velocity field, distorted by the gravitational attraction of the local large scale structure, and the reddening law appear at the moment the major limitations in the accuracy with which cosmological parameters can be determined. These absorption effects can introduce a secondary bias into the observations of the distant supernovae, which needs to be carefully evaluated. Supernovae have been used for the measurement of the Hubble constant, i.e. the current expansion rate of the universe, and the accelerated cosmic expansion directly inferred from the apparent faintness of the distant supernovae.     

Evidence for dark energy from the cosmic microwave background alone using the Atacama Cosmology Telescope lensing measurements

For the first time, measurements of the cosmic microwave background radiation (CMB) alone favor cosmologies with w = -1 dark energy over models without dark energy at a 3.2-sigma level. We demonstrate this by combining the CMB lensing deflection power spectrum from the Atacama Cosmology Telescope with temperature and polarization power spectra from the Wilkinson Microwave Anisotropy Probe. The lensing data break the geometric degeneracy of different cosmological models with similar CMB temperature power spectra. Our CMB-only measurement of the dark energy density Ω(Λ) confirms other measurements from supernovae, galaxy clusters, and baryon acoustic oscillations, and demonstrates the power of CMB lensing as a new cosmological tool.     

Tycho’s supernova remnant as a source of cosmic rays in our galaxy

The Tycho’s supernova remnant was observed using the SHALON atmospheric Cherenkov telescope at the Tien Shan High-Altitude Observatory. This object has long been considered to be a candidate for sources of cosmic ray hadrons in the Northern Hemisphere. In [1, 2], the Tycho’s properties were described using the nonlinear kinetic model of cosmic ray acceleration in supernovae remnants. The expected γ-ray flux from π ⁰-decay extends to energies > 30 eV, whereas the γ-ray photon flux generated by inverse Compton scattering is cut off above several TeV. Therefore, the detection of γ-rays at energies of 10–80 TeV by the SHALON telescope is an indication of their hadron origin. From the SHALON telescope data, additional information on such parameters of the Tycho’s supernova remnant as the distance and interstellar medium density was obtained within the theory [1, 2].     

New dark energy constraints from supernovae, microwave background, and galaxy clustering

Using supernova, cosmic microwave background, and galaxy clustering data, we make the most accurate measurements to date of the dark energy density rho(X) as a function of cosmic time, constraining it in a rather model-independent way, assuming a flat universe. We find that Einstein's simplest scenario, where rho(X)(z) is constant, remains consistent with these new tight constraints and that a big crunch or big rip is more than 50 Gyr away for a broader class of models allowing such cataclysmic events. We discuss popular pitfalls and hidden priors.     

Value of the Cosmological Constant in the Cosmological Relativity Theory

It is shown that the cosmological relativity theory predicts the value = 1.934 × 10^–35s^–2 for the cosmological constant. This value of is in excellent agreement with the measurements recently obtained by the High-Z Supernova Team and the Supernova Cosmology Project.     

Living with lambda

This talk presents a brief overview of recent results pertaining to the cosmological constant ‘A’. I summarize the observational situation focussing on observations of high redshift Type Ia supernovae which suggest A > 0. Observations of small angular anisotropies in the cosmic microwave background complement Type Ia supernovae observations and both CMB and Sn can be combined to place strong constraints on the value of A. The presence of a small A-term increases the age of the universe and slows down the formation of large scale structure. I also review recent theoretical attempts to generate a small A-term at the current epoch and a model independent approach for determining the cosmic equation of state.     

Maximum energy of cosmic rays accelerated in supernova remnants

Amplification of the magnetic field in young supernova remnants leads to the corresponding increase in the maximum energy of particles approximately to the knee energy 3 × 10¹⁵ eV at the end of the free expansion stage. The knee in the spectrum of cosmic rays is due to the transition of the supernova remnant from the free expansion stage to the Sedov stage. The knee energy is calculated for different types of supernovae. The maximum energy of accelerated particles teaches Z × 10¹⁷ eV for the observed remnant expansion velocities.     

Dedicated supernova detection by a network of neutral current spherical TPC detectors

Supernova neutrinos can easily be detected by a spherical gaseous TPC detector measuring very low energy nuclear recoils. The expected rates are quite large for a neutron-rich target since the neutrino-nucleus neutral current interaction yields a coherent contribution of all neutrons. As a matter of fact, for a typical supernova at 10 kpc, about 1000 events are expected using a spherical detector of radius 4 m with Xe gas at a pressure of 10 atm. A worldwide network of several such simple, stable, and low-cost supernova detectors with a running time of a few centuries is quite feasible. The text was submitted by the authors in English.     

Observational probes of cosmic acceleration

The accelerating expansion of the universe is the most surprising cosmological discovery in many decades, implying that the universe is dominated by some form of “dark energy” with exotic physical properties, or that Einstein’s theory of gravity breaks down on cosmological scales. The profound implications of cosmic acceleration have inspired ambitious efforts to understand its origin, with experiments that aim to measure the history of expansion and growth of structure with percent-level precision or higher. We review in detail the four most well established methods for making such measurements: Type Ia supernovae, baryon acoustic oscillations (BAO), weak gravitational lensing, and the abundance of galaxy clusters. We pay particular attention to the systematic uncertainties in these techniques and to strategies for controlling them at the level needed to exploit “Stage IV” dark energy facilities such as BigBOSS, LSST, Euclid, and WFIRST  . We briefly review a number of other approaches including redshift-space distortions, the Alcock–Paczynski effect, and direct measurements of the Hubble constant _H0$H_0$. We present extensive forecasts for constraints on the dark energy equation of state and parameterized deviations from General Relativity, achievable with Stage III and Stage IV experimental programs that incorporate supernovae, BAO, weak lensing, and cosmic microwave background data. We also show the level of precision required for clusters or other methods to provide constraints competitive with those of these fiducial programs. We emphasize the value of a balanced program that employs several of the most powerful methods in combination, both to cross-check systematic uncertainties and to take advantage of complementary information. Surveys to probe cosmic acceleration produce data sets that support a wide range of scientific investigations, and they continue the longstanding astronomical tradition of mapping the universe in ever greater detail over ever larger scales.     

TeV neutrinos from core collapse supernovae and hypernovae

A fraction of core-collapse supernovae of type Ib/c are associated with gamma-ray bursts, which are thought to produce highly relativistic jets. Recently, it has been hypothesized that a larger fraction of core-collapse supernovae produce slower jets, which may contribute to the disruption and ejection of the supernova envelope, and explain the unusually energetic hypernovae. We explore the TeV neutrino signatures expected from such slower jets, and calculate the expected detection rates with upcoming Gigaton Cherenkov experiments. We conclude that individual jetted supernovae may be detectable from nearby galaxies.     

Einstein,de Sitter and the beginning of relativistic cosmology in 1917

In 1917, both Einstein and de Sitter proposed a new interpretation of the universe as a whole: the structure of the universe could be described in terms of relativistic field equations. Their contributions marked the beginning of the modern scientific comprehension of the origin and evolution of the universe. Our aim is to propose a critical review paper, based on references in primary sources, on the formulation in 1917 of Einstein’s and de Sitter’s models of the universe, which represents a fundamental chapter in the history of relativistic Cosmology.     

SNO and supernovae

The Sudbury Neutrino Observatory (SNO) has unique capabilities as a supernova detector. In the event of a galactic supernova there are opportunities, with the data that SNO would collect, to constrain certain intrinsic neutrino properties significantly, to test details of the various models of supernova dynamics, and to provide prompt notification to the astronomical community through the Supernova Early Warning System (SNEWS). This paper consists of a discussion of these opportunities illustrated by some preliminary Monte Carlo results.     

Detection of the power spectrum of cosmic microwave background lensing by the Atacama Cosmology Telescope

We report the first detection of the gravitational lensing of the cosmic microwave background through a measurement of the four-point correlation function in the temperature maps made by the Atacama Cosmology Telescope. We verify our detection by calculating the levels of potential contaminants and performing a number of null tests. The resulting convergence power spectrum at 2° angular scales measures the amplitude of matter density fluctuations on comoving length scales of around 100 Mpc at redshifts around 0.5 to 3. The measured amplitude of the signal agrees with Lambda cold dark matter cosmology predictions. Since the amplitude of the convergence power spectrum scales as the square of the amplitude of the density fluctuations, the 4σ detection of the lensing signal measures the amplitude of density fluctuations to 12%.     

Detection of neutrinos from supernovae in nearby galaxies

While existing detectors would see a burst of many neutrinos from a Milky Way supernova, the supernova rate is only a few per century. As an alternative, we propose the detection of approximately 1 neutrino per supernova from galaxies within 10 Mpc, in which there were at least 9 core-collapse supernovae since 2002. With a future 1 Mton scale detector, this could be a faster method for measuring the supernova neutrino spectrum, which is essential for calibrating numerical models and predicting the redshifted diffuse spectrum from distant supernovae. It would also allow a > or approximately 10(4) times more precise trigger time than optical data alone for high-energy neutrinos and gravitational waves.     

海量星系光谱中的超新星候选范围自动约减

超新星是恒星世界中已知道的最剧烈的天文现象之一,但目前发现的超新星数量相比于已探测到的数百亿天体而言又是有限的,所以有必要寻找快速高效的超新星搜寻方法或辅助手段。拟在Ⅰa型超新星统计特征描述的基础上提出了一种海量星系光谱下Ⅰa型超新星候选体选择范围自动约减的方法。该方法首先对Ⅰa型超新星模板PCA分析获得特征谱,并获得每条待检星系光谱的低维超新星特征描述,然后通过引入样本的局部孤立性因子进行离群搜索,最后获得总样本数的1%作为继续搜寻证认超新星候选体选择的初始范围。实验表明该方法有效可行,这一方法在海量光谱中自动去除大量不含超新星的星系光谱,为超新星的进一步搜寻证认和后续观测提供了较可靠的候选范围,从而成为直接利用光谱巡天的海量数据获得超新星的高效途径。