Search for charged massive long-lived particles

We report on a search for charged massive long-lived particles (CMLLPs), based on 5.2 fb(-1) of integrated luminosity collected with the D0 detector at the Fermilab Tevatron pp collider. We search for events in which one or more particles are reconstructed as muons but have speed and ionization energy loss (dE/dx) inconsistent with muons produced in beam collisions. CMLLPs are predicted in several theories of physics beyond the standard model. We exclude pair-produced long-lived gauginolike charginos below 267 GeV and Higgsino-like charginos below 217 GeV at 95% C.L., as well as long-lived scalar top quarks with mass below 285 GeV.     

Exotic relics from the big bang

New, exotic (very heavy and/or very weakly interacting) particles would have been produced in the hot, dense environment of the early Universe. If sufficiently long-lived, some exotic relics would have survived to influence the subsequent evolution of the Universe; some may be present today. The laboratory and astrophysical information which can constrain the properties of such new particles is outlined and guidelines are presented for testing models of elementary particle physics.     

Supersymmetric relics from the big bang

We consider the cosmological constraints on supersymmetric theories with a new, stable particle. Circumstantial evidence points to a neutral gauge/Higgs fermion as the best candidate for this particle, and we derive bounds on the parameters in the lagrangian which govern its mass and couplings. One favored possibility is that the lightest neutral supersymmetric particle is predominantly a photino $\text{～}\text{γ}$ with mass above $\text{1}\text{2}$ GeV, while another is that the lightest neutral supersymmetric particle is a Higgs fermion with mass above 5 GeV or less than O(100) eV. We also point out that a gravitino mass of 10 to 100 GeV implies that the temperature after completion of an inflationary phase cannot be above 10¹⁴ GeV, and probably not above 3 × 10¹² GeV. This imposes constraints on mechanisms for generating the baryon number of the universe.     

Neutrino astronomy: Present and future

I briefly review the present and future status of the burgeoning field of neutrino astronomy. I outline the astrophysics and particle physics goals, design, and performance of the various current and proposed neutrino telescopes. Also described are present results and future expectations.     

Quantum nature of the big bang

Some long-standing issues concerning the quantum nature of the big bang are resolved in the context of homogeneous isotropic models with a scalar field. Specifically, the known results on the resolution of the big-bang singularity in loop quantum cosmology are significantly extended as follows: (i) the scalar field is shown to serve as an internal clock, thereby providing a detailed realization of the "emergent time" idea; (ii) the physical Hilbert space, Dirac observables, and semiclassical states are constructed rigorously; (iii) the Hamiltonian constraint is solved numerically to show that the big bang is replaced by a big bounce. Thanks to the nonperturbative, background independent methods, unlike in other approaches the quantum evolution is deterministic across the deep Planck regime.     

Pregeometric origin of the big bang

The temperature-dependent effective action for gravity is calculated in pregeometry. It indicates that the effective potential for the space-time metric has the minimum at the origin for extremely high temperature. The origin of the big bang can be taken as a local and spontaneous phase transition of the space-time from the pregeometric phase to the geometric one.     

Was the big bang a whimper?

In many cases the spatially homogeneous cosmological models of General Relativity begin or end at a “big bang” where the density and temperature of the matter in the universe diverge. However in certain cases the spatially homogeneous development of these universes terminates at a singularity where all physical quantities are well—behaved (a “whimper”) and an associated Cauchy horizon. We examine the existence and nature of these singularities, and the possible fate of matter which crosses the Cauchy horizon in such a universe. The nature of both kinds of singularity is illustrated by simple models based on two-dimensional Minkowski space-time; and the possibility of other types of singularity occuring is considered.     

Strange matter and big bang helium synthesis

Stable strange quark matter produced in the QCD phase transition in the early universe will trap neutrons and repel protons, thus reducing primordial helium production, Y_p. For reasonable values of Y_p, the radius of strange droplets must exceed 10^?6 cm if strange matter shall solve the dark-matter problem without spoiling Big Bang helium synthesis.     

Neutrino geophysics and astronomy at Baksan Neutrino Observatory: Potential of the spectroscopy of natural antineutrino sources

Prospects for studying, at the Baksan Neutrino Observatory, geoneutrinos, as well as neutrinos from supernovae, by means of a scintillation spectrometer having a target mass of 5000 t are considered. It is shown that the geographical location, a deep position (4800 mwe), and a modest background of antineutrinos from nuclear reactors makes the Baksan Neutrino Observatory one of the best places for performing such investigations. Particular attention is given to the derivation of information about the nature of neutrinos, the possibility of detecting relic neutrinos from supernovae, and the discovery of a hypothetical georeactor.     

大爆炸和宇宙学红移中常被误解的几个观念

列举了大爆炸和宇宙学中几个常被误解的问题,并给出了正确的解释.     

Search for long-lived charged massive particles in pp collisions at square root s = 1.8 TeV

We report a search for the production of long-lived charged massive particles in a data sample of 90 pb(-1) of square root[s]=1.8 TeV pp collisions recorded by the Collider Detector at Fermilab. The search uses the muonlike penetration and anomalously high ionization energy loss signature expected for such a particle to discriminate it from backgrounds. The data are found to agree with background expectations, and cross section limits of O(1) pb are derived using two reference models, a stable quark and a stable scalar lepton.     

Constraining antimatter domains in the early universe with big bang nucleosynthesis

We consider the effect of a small-scale matter-antimatter domain structure on big bang nucleosynthesis and place upper limits on the amount of antimatter in the early universe. For small domains, which annihilate before nucleosynthesis, this limit comes from underproduction of 4He. For larger domains, the limit comes from 3He overproduction. Since most of the 3He from &pmacr; 4He annihilation are themselves annihilated, the main source of primordial 3He is the photodisintegration of 4He by the electromagnetic cascades initiated by the annihilation.     

Photon condensation in the big bang cosmology and longitudinal background radiation of the universe

With the assumption of nonzero photon mass the existence of the photon condensate at the early stages of the Universe's expansion is supposed. Evaporation of the condensate leads then to the formation of intensive longitudinal background radiation.