ISSN:0094-243X    

DOI:10.1063/1.48364

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Traditional evidence for large amount of dark matter is based on dynamical consideration for systems withtdyn≫tobs. Recent observational and theoretical developments in gravitational lensing offer a much more robust determination of the mass distribution in some galaxies and their clusters, with the precision comparable to that obtainable for double stars for whichtdyn<tobs, and offer independent and direct evidence for the presence of dark matter. Gravitational microlensing and femtolensing offer a possibility to detect MACHOs with masses in excess of ∼10−15M⊙. The recent detections of microlensing events by the EROS, MACHO and OGLE teams do not require any dark lenses as ordinary low mass stars are compatible with the observations. However, these searches will soon either detect genuine MACHOs, or they will place stringent upper limits on their number density. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.48316

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The standard model of particle physics is marvelously successful. However, it is obviously not a complete or final theory. I shall argue here that the structure of the standard model gives some quite concrete, compelling hints regarding what lies beyond. Taking these hints seriously, one is led to predict the existence of new types of very weakly interacting matter, stable on cosmological time scales and produced with cosmologically interesting densities–that is, ‘‘dark matter’’. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.48314

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The existence of a finite neutrino mass would have important consequences in particle physics, astrophysics, and cosmology. Experimental sensitivities have continued to be pushed down without any confirmed evidence for a finite neutrino mass. Yet there are several observations which might be possible indications of a finite neutrino mass. If these hints are confirmed, then it is likely that at least one of the neutrinos has a mass in the eV range. As such, it would be a prime candidate for the hot dark matter that seems to be required to explain a number of observations of the large‐scale structure of the Universe. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.48374

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A dark matter (DM) search experiment was flown on the IMAX balloon payload to search for a possible minor component of the dark matter in the Galactic halo: ionizing massive particles (IMPs) (mx≳104GeV/c2) that cannot penetrate the atmosphere due to their low‐velocities and high energy‐loss. The DM search experiment consisted of a delayed coincidence between four large plastic scintillation detectors arranged in a vertical stack. In order to search for ultra‐slow particles which do not slow down in the IMAX telescope, the experiment contained TDCs which measured the time‐delayTi,i+1∈(0.3, 14.0) &mgr;s between hits in successive counters to ∼2% precision. We present IMP flux limits for non‐slowing IMPs and also for IMPs which slow down significantly within the IMAX telescope. This experiment effectively closes much of a previously unconstrained ‘‘window’’ in the mass/cross‐section joint parameter spaces for massive particles as the dominant halo DM. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.48386

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Dark matter, both as a concept and as a name, has a surprisingly long history. We here trace its story from 19th century origins in the Newtonian two‐ and three‐body problems through early 20th century applications of velocity dispersions of stars and galaxies to the first considerations of the most promising modern candidates. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.48345

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.48346

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We review recent gravitational microlensing results from the EROS, MACHO, and OGLE collaborations, and present some details of the very latest MACHO results toward the Galactic Bulge, The MACHO collaboration has now discovered in excess of 40 microlensing events toward the Galactic Bulge during the 1993 observing season. A preliminary analysis of this data suggests a much higher microlensing optical depth than predicted by standard galactic models suggesting that these models will have to be revised. This may have important implications for the structure of the Galaxy and its dark halo. Also shown are MACHO data of the first microlensing event ever detected substantially before peak amplification, the first detection of parallax effects in a microlensing event, and the first caustic crossing to be resolved in a microlensing event. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.48390

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Halo and disk M dwarfs differ significantly in metallicity. Multi‐color deep CCD surveys are uniquely capable of detecting these separate populations of stars with differing metallicity and therefore colors. Analyzing very deep three‐band CCD images covering 192 arcmin2at high galactic latitude we find no evidence for a population of extreme low mass M subdwarfs sufficient to account for the halo dark matter. These observations covering a volume of 2×105pc3are consistent with extrapolations of a halo luminosity function determined using low metallicity stars in the solar neighborhood. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.48347

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Gravitational microlensing in the direction of Q0957+561 A, B (TwQSO) is expected to show the spectrum of mass objects in thez=0.37 lens galaxy, because the existence of a widely separated double image implies a microlensing optical depth near unity. In our 15 year record of brightness of the two quasar images, we find evidence for a range of masses from approximately 0.1Moto 10−5Mo. These are evidenced by continuous power in the Fourier power spectrum of the observed microlensing over a range of frequencies from 0.1 to 4 cycles per year. A sharp high frequency cutoff (lower mass bound) is found. ©1995 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.48348

出版商:AIP    

年代:1995

数据来源: AIP