摘要:

A higher dimensional cosmological model is proposed where an expanding universe evolves from the vacuum fluctuation and matter creation takes place out of the gravitational energy. Choosing a particular form of the matter creation functionN(t)as an initial conditions it can be shown that starting from an inflationary era the cosmos enters the higher dimensional Friedmann-like phase after a time scale when the matter creation stops. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419535

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419536

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

I explore several possible solutions to the “missing satellites” problem that challenges the collisionless cold dark matter model. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419537

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Recent results from Super-Kamiokande on atmospheric neutrinos, solar neutrinos and supernova neutrinos are presented. The atmospheric neutrino data shows an evidence for&ngr;&mgr;oscillations in the ratio of&ngr;&mgr;/&ngr;eand zenith angle distributions of &mgr;-like events. The neutrino oscillation parameters obtained from the atmospheric neutrino data are&Dgr;m2=(1.7−4)×10−3 eV2andsin2&hthinsp;2&thgr;>0.89for&ngr;&mgr;↔&ngr;&tgr;oscillations. The zenith angle distributions of higher energy atmospheric neutrino data show that the pure&ngr;&mgr;↔&ngr;&tgr;oscillations are favored over the pure&ngr;&mgr;↔&ngr;sterileoscillations. The analyses of solar neutrino data on day/night difference in flux and spectral shape of8Bsolar neutrinos constrained the oscillation parameters for&ngr;eoscillations. The small mixing angle solution and just-so solutions are disfavored with about 95&percent; C.L. The flux constrained analysis of day/night and energy spectrum favours large mixing solutions. The huge Super-Kamiokande detector is able to detect ∼4000 neutrino events, if a supernova happens at the center of our galaxy. No neutrino burst has been observed at SK yet. Progress of the search for relic supernova neutrinos is also discussed. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419538

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

DAMA is searching for rare processes by developing and using several kinds of radiopure scintillators: NaI(Tl), liquid Xenon andCaF2(Eu).Here, in particular, results achieved during four annual cycles with a model independent analysis and with model dependent ones in the investigation of the so-called WIMP annual modulation signature are summarized. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419539

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We report on the latest results from the CDMS (cryogenic dark matter search) experiment. The experiment uses superconducting particle detectors, operated below 100 mK, to search for dark matter in the form of weakly interacting massive elementary particles or WIMPs. These detectors are either Si or Ge crystals, where the electron-hole production and the phonon production are measured for each event, allowing the discrimination of electron recoils (most backgrounds due to gammas and betas) from nuclear recoils (due to WIMPs and neutrons). We have recently reported new limits from the Stanford shallow site experiment (CDMS-I) which explore supersymmetric models where the lightest supersymmetric particle is often an excellent WIMP candidate. We will also report on the Soudan deep site facility for the CDMS-II experiment which is under construction, and on the status of the CDMS-II detector fabrication. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419540

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

When microlensing surveys were first undertaken a decade ago, their focus was overwhelmingly on dark matter. They have indeed fulfilled their original promise by ruling out massive compact halo objects (Machos) as the dominant form of dark matter over 8 decades of mass. However, microlensing has now developed a number of other important applications including searching for planets and probing the atmospheres of stars. More applications are promised in both the near and distant future. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419541

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

I discuss recent results from the numerical CDM simulations concerning the density profiles of galactic halos and the abundance of satellite dark matter halos around galaxies. The models predict 1) halo density distributions that may be too concentrated compared to the density distributions implied by observed galactic rotation curves and 2) ≳5–10 times more satellites than are actually observed around the Milky Way and M31. This may indicate that there are either physical mechanisms at work which complicate the straightforward comparison between observations and dissipationless simulations (e.g., processes that greatly reduce the starformation efficiency in most satellite halos and render them invisible), or that essential physics is missing in the CDM models. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419542

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Warm Dark Matter (WDM) models have recently been resurrected to resolve apparent conflicts of Cold Dark Matter (DM) models with observations. Endowing the DM particles with non-negligible velocities causes free-streaming, which suppresses the primordial power spectrum on small scales. The choice of a root-mean-square velocity dispersionvrms,0∼0.05 km/sat redshiftz=0(corresponding to a particle massmX∼1 keVif the WDM particles are fermions decoupling while relativistic) helps alleviate most, but probably not all, of the small-scale problems faced by CDM. An important side-effect of the particle velocities is the severe decrease in the number of collapsed halos at high redshift. This is caused both by the loss of small-scale power, and by the delay in the collapse of the smallest individual halos (with masses near the effective Jeans mass of the DM). The presence of early halos is required in order (1) to host either early quasars or galaxies that can reionize the universe by redshiftz=5.8,and (2) to allow the growth of the supermassive black hole believed to power the recently discovered quasar SDSS 1044-1215 at this redshift. We quantify these constraints using a modified Press-Schechter formalism, and findvrms,0≲0.04 km/s(ormX≳1 keV). If future observations uncover massive black holes atz≳10,or reveal that reionization occurred atz≳10,this could conclusively rule out WDM models as the solution to the small-scale crisis of the CDM paradigm. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419543

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Adaptive SPH and N-body simulations were carried out to study the evolution of the equilibrium structure of dark matter halos that result from the gravitational instability and fragmentation of cosmological pancakes. Such halos resemble those formed by hierarchical clustering from realistic initial conditions in a CDM universe and, therefore, serve as a test-bed model for studying halo dynamics. The dark matter density profile is close to the universal halo profile identified previously from N-body simulations of structure formation in CDM, with a total mass and concentration parameter which grow linearly with scale factora. When gas is included, this concentration parameter is slightly larger than the pure N-body result. We also find that the dark matter velocity distribution is less isotropic and more radial than found by N-body simulations of CDM. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419544

出版商:AIP    

年代:1901

数据来源: AIP