scholarly journals Maximum Absorption of the Global 21 cm Spectrum in the Standard Cosmological Model

2021 ◽  
Vol 923 (1) ◽  
pp. 98
Author(s):  
Yidong Xu ◽  
Bin Yue ◽  
Xuelei Chen

Abstract The absorption feature in the global spectrum is likely the first 21 cm observable from the cosmic dawn, which provides valuable insights into the earliest history of structure formation. We run a set of high-resolution hydrodynamic simulations of early structure formation to assess the effect of nonlinear structure formation on the maximum absorption level (i.e., assuming the spin temperature coupling is saturated) of the global 21 cm spectrum in the standard cosmological framework. We ignore the star formation and feedbacks, which also tend to reduce the absorption signal, but take into account the inevitable nonlinear density fluctuations in the intergalactic medium (IGM), shock-heating, and Compton-heating, which can reduce the absorption level. We found that the combination of these reduced the maximum absorption signal by ∼15% at redshift 17, as compared with the homogeneous or linearly-fluctuating IGM. These effects have to be carefully accounted for when interpreting the observational results, especially when considering the necessity of introducing new physics.

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Lorenzo Calibbi ◽  
Francesco D’Eramo ◽  
Sam Junius ◽  
Laura Lopez-Honorez ◽  
Alberto Mariotti

Abstract Displaced vertices at colliders, arising from the production and decay of long-lived particles, probe dark matter candidates produced via freeze-in. If one assumes a standard cosmological history, these decays happen inside the detector only if the dark matter is very light because of the relic density constraint. Here, we argue how displaced events could very well point to freeze-in within a non-standard early universe history. Focusing on the cosmology of inflationary reheating, we explore the interplay between the reheating temperature and collider signatures for minimal freeze-in scenarios. Observing displaced events at the LHC would allow to set an upper bound on the reheating temperature and, in general, to gather indirect information on the early history of the universe.


Author(s):  
Monique C. Aller ◽  
Varsha P. Kulkarni ◽  
Donald G. York ◽  
Daniel E. Welty ◽  
Giovanni Vladilo ◽  
...  

AbstractGas and dust grains are fundamental components of the interstellar medium and significantly impact many of the physical processes driving galaxy evolution, such as star-formation, and the heating, cooling, and ionization of the interstellar material. Quasar absorption systems (QASs), which trace intervening galaxies along the sightlines to luminous quasars, provide a valuable tool to directly study the properties of the interstellar gas and dust in distant, normal galaxies. We have established the presence of silicate dust grains in at least some gas-rich QASs, and find that they exist at higher optical depths than expected for diffuse gas in the Milky Way. Differences in the absorption feature shapes additionally suggest variations in the silicate dust grain properties, such as in the level of grain crystallinity, from system-to-system. We present results from a study of the gas and dust properties of QASs with adequate archival IR data to probe the silicate dust grain properties. We discuss our measurements of the strengths of the 10 and 18 μm silicate dust absorption features in the QASs, and constraints on the grain properties (e.g., composition, shape, crystallinity) based on fitted silicate profile templates. We investigate correlations between silicate dust abundance, reddening, and gas metallicity, which will yield valuable insights into the history of star formation and chemical enrichment in galaxies.


2019 ◽  
Author(s):  
B. Lee Roberts

I discuss the history of the muon (g-2)(g−2) measurements, beginning with the Columbia-Nevis measurement that observed parity violation in muon decay, and also measured the muon gg-factor for the first time, finding g_\mu=2gμ=2. The theoretical (Standard Model) value contains contributions from quantum electrodynamics, the strong interaction through hadronic vacuum polarization and hadronic light-by-light loops, as well as the electroweak contributions from the WW, ZZ and Higgs bosons. The subsequent experiments, first at Nevis and then with increasing precision at CERN, measured the muon anomaly a_\mu = (g_\mu-2)/2aμ=(gμ−2)/2 down to a precision of 7.3 parts per million (ppm). The Brookhaven National Laboratory experiment E821 increased the precision to 0.54 ppm, and observed for the first time the electroweak contributions. Interestingly, the value of a_\muaμ measured at Brookhaven appears to be larger than the Standard Model value by greater than three standard deviations. A new experiment, Fermilab E989, aims to improve on the precision by a factor of four, to clarify whether this result is a harbinger of new physics entering through loops, or from some experimental, statistical or systematic issue.


2021 ◽  
Vol 30 (11) ◽  
pp. 2-7
Author(s):  
Jae-Hyeon KO

The first issue of the journal “New Physics: Sae Mulli”, one of the representative journals of the Korean Physical Society, was published in May 1961. Since then, Sae Mulli has evolved as an important platform for sharing new findings with those members belonging to the Korean Physical Society. This article presents a brief review of the history of this journal. It also includes the current status of and prospects for this journal.


Author(s):  
Peter T. Manicas

The history of social science can conveniently be divided into four uneven periods, starting with the beginnings of both western science and philosophy in the ancient Greek polis (city or state). It is fair to say, with qualifications, that the debate generated by the so-called Sophists, professional teachers of rhetoric in fifth-century Athens, established what would become the central questions for the future. The fundamental issue could be put thus: is society ‘natural’ or is it ‘conventional’, a historical product of human activities which vary across time and space? The Sophists, often abused in our standard histories, supported the conventional view. They held that even if it was anthropologically necessary that Homo sapiens live in societies, nature was silent about the character and ends of society. They thus defended what might be called ‘cultural relativism’. By contrast Aristotle argued that some men were ‘naturally’ slaves and that all women were ‘naturally’ inferior; therefore slavery and patriarchy were dictated by nature, a view that prevailed well into the early modern period. Beginning in the sixteenth century we find a host of thinkers who reconceived the problem first raised by the Sophists. Many of them, for example, Hobbes, Rousseau and Adam Smith, held that ‘by nature’ humans had similar capacities and powers. Inequalities of power were ‘artificial’, wholly the result of historically established conventions. These writers also rejected the idea that society was a kind of natural community. For many of them, society existed by consent, the result of a contract. The rejection of Aristotelianism was inspired by the Copernican revolution and the new physics of Galileo and Newton. This produced a self-conscious effort by early modern writers to articulate the idea of human science, modelled on the new physics. This critical idea was well put by the physiocrat Francois Quesnay: ‘All social facts are linked together in the bond of eternal, immutable, ineluctable, inevitable laws, which individuals and government would obey if they were once known to them’ (Randall 1940: 323). The third period, roughly the nineteenth century, is then a battleground over both the idea of science and the idea of a human science. The paradigm provided by celestial mechanics was nearly overwhelming; even so, there was disagreement as regards its character, especially as regards the question of causality and explanation. Until very recently, ‘positivists’ have tended to prevail. That is, writers have followed Auguste Comte, who gave us the terms ‘positivism’ and ‘sociology’, and who held there were social laws which were to be analysed as ‘relations of invariable succession’: whenever this, then that. As regards the possibility of a human science, consciousness and the problem of a free will raised the biggest questions. Materialists found nothing special about either; idealists did. Indeed a surprising amount of the most recent debates in the philosophy of the social sciences have their roots in these issues. If, as positivists insist, activity is governed by law, then what of human freedom? On the other hand, if humans have collectively made society and thus can remake it, then what is the nature of a human science?


1992 ◽  
Vol 9 ◽  
pp. 319-321
Author(s):  
J. Richard Bond

Constraints on models of cosmic structure formation that can be drawn from current limits on large angle microwave background anisotropies are now competitive with those from recent small and intermediate angle experiments and are relatively insensitive to the reheating history of the Universe. Here I give limits on Gaussian scale invariant adiabatic fluctuations and describe the role that the large angle results play in constraining models with enhanced large distance galaxy clustering power inferred from correlation function measurements is described.


2018 ◽  
Vol 620 ◽  
pp. A97 ◽  
Author(s):  
M. Salz ◽  
S. Czesla ◽  
P. C. Schneider ◽  
E. Nagel ◽  
J. H. M. M. Schmitt ◽  
...  

We present three transit observations of HD 189733 b obtained with the high-resolution spectrograph CARMENES at Calar Alto. A strong absorption signal is detected in the near-infrared He I triplet at 10830 Å in all three transits. During mid-transit, the mean absorption level is 0.88 ± 0.04% measured in a ±10 km s−1 range at a net blueshift of − 3.5 ± 0.4 km s−1 (10829.84–10830.57 Å). The absorption signal exhibits radial velocities of + 6.5 ± 3.1 km s−1 and − 12.6 ± 1.0 km s−1 during ingress and egress, respectively; all radial velocities are measured in the planetary rest frame. We show that stellar activity related pseudo-signals interfere with the planetary atmospheric absorption signal. They could contribute as much as 80% of the observed signal and might also affect the observed radial velocity signature, but pseudo-signals are very unlikely to explain the entire signal. The observed line ratio between the two unresolved and the third line of the He I triplet is 2.8 ± 0.2, which strongly deviates from the value expected for an optically thin atmospheres. When interpreted in terms of absorption in the planetary atmosphere, this favors a compact helium atmosphere with an extent of only 0.2 planetary radii and a substantial column density on the order of 4 × 1012 cm−2. The observed radial velocities can be understood either in terms of atmospheric circulation with equatorial superrotation or as a sign of an asymmetric atmospheric component of evaporating material. We detect no clear signature of ongoing evaporation, like pre- or post-transit absorption, which could indicate material beyond the planetary Roche lobe, or radial velocities in excess of the escape velocity. These findings do not contradict planetary evaporation, but only show that the detected helium absorption in HD 189733 b does not trace the atmospheric layers that show pronounced escape signatures.


1999 ◽  
Vol 183 ◽  
pp. 273-273
Author(s):  
K. Yamamoto ◽  
N. Sugiyama ◽  
H. Sato

We carefully re-examine the evolution of small scale cosmological perturbations, motivated from the studies of cosmic structure formation in the high-z universe. Under the assumption of the hierarchical clustering scenario, the evolution of density fluctuations on very small scales is especially important for the early formation of the bound objects such as population III stars or primordial sub-galaxies.


2020 ◽  
Vol 102 (10) ◽  
Author(s):  
Giovanni Manfredi ◽  
Jean-Louis Rouet ◽  
Bruce N. Miller ◽  
Gabriel Chardin

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