INTRODUCTION TO THE

“THIRD BRAZILIAN WORKSHOP ON NEW PHYSICS FROM SPACE”

 

REUVEN OPHER

(IAG-USP)

---

WHAT WERE THE IMPORTANT RESULTS IN THE LAST YEAR?

 

The program of this workshop covers the main topics of “New Physics From Space”. During this third workshop, the speakers will emphasize recent work which is of particular importance in their area, in addition to presenting some of their own work. Appreciable time has been set aside for discussion of the talks, which in the past workshops has been very animated. In order to illustrate the interest shown by the international scientific community in the topics covered in our workshop, I will discuss briefly in this introductory talk some of the results published during the past year in these areas which I feel were particularly important and which would be interesting to discuss during the workshop.

 

1) Cosmic Rays

 

1-A) Shock Accelerated Cosmic Rays

The standard manner to accelerate cosmic rays < 10¹⁵ eV is by first order Fermi acceleration in astrophysical (e.g., supernova) shocks. A semi-analytical approach to non-linear shock acceleration has been given [1-1].

1-B) UHECR Due To Hydromagnetic Turbulence

A major problem in cosmic rays that still remains is how to produce cosmic rays >10²⁰eV. One recently suggested source of UHECR (ultra-high cosmic rays) is hydromagnetic turbulence. It was found that the properties of small scale hydromagnetic turbulence are fundamentally changed in the presence of cosmic rays. As a result, magnetic fields which are several orders of magnitude weaker than present galactic fields can accelerate and retain a population of relativistic cosmic rays, perhaps even of >10²⁰eV [1-2].

1-C) UHECR From Magnetars

Another recently suggested source of ultra-high energy cosmic rays is magnetars, rotating neutron stars with magnetic fields > 10¹⁵ G. Relativistic winds of newly born magnetars can create cosmic rays up to 10²¹ – 10²²eV [1-3].

1-D) UHECR From Wimpzillas Created In The Inflation Reheating Era

It was suggested that Wimpzillas, with masses > 10²⁰ eV/c², could be created during the reheating phase following inflation. Their decay could then produce the UHECR. It was recently shown that inflaton decay products (e.g., Wimpzillas) acquire plasma masses, which can render inflaton decay kinematicaly forbidden, effecting Wimpzilla production    [1-4].

1-E) UHECR From Cosmic Strings Or Wimpzillas Due To A Violation Of Lorentz Invariance

In a top-down scenario of UHECR from cosmic strings or Wimpzillas (particles with masses > 10²⁰ eV/c²), photons are generally predicted to be the primary constituent. The UHECR data that we have indicate, however, a hadronic primary. It was recently suggested that a slight violation of Lorentz invariance could result in photon decay making neutrons the primary particles of UHECR in top-down scenarios [1-5].

1-F) UHECR From GRBs

It was shown that the total energy budget of GRBs easily accounts for the energy injection rate necessary to account for UHECRs [1-6].

1-G) UHECR From Dark Matter Annihilation

Annihilation of clumped superheavy dark matter (e.g., Wimpzillas) provides an interesting explanation for the origin of UHECR [1-7].

 

2) Neutrino Astrophysics

 

2-A) Solar Neutrinos

Until recently, the major problem in neutrino astrophysics was the explanation of the small number of solar neutrinos detected. The Sudbury Neutrino Observatory has solved this 30 year old mystery by showing that neutrinos from the sun change species on the way to the earth [2-1]. The recent KAMLAND detector results indicate that only the large mixing angle solution is possible with a difference in mass of the two mixing species Δm ~ 10^-2 eV.

2-B) Supernova Neutrinos

The core collapse of a massive star in the Milky Way produces a neutrino burst intense enough to be detected by existing neutrino detectors. The AMANDA telescope, deep in the South Pole ice, could detect these MeV neutrinos. No candidate, however, has been detected [2-2].

 

3) Gamma Ray Bursts (GRBs)

 

Observations of GRB afterglows place them at cosmological distances. However their origin is still a mystery [3-1].

3-A) Evidence For A Varying Energy Source

An optical counterpart of the gamma ray burst GRB 021004 has been reported, only 193 seconds after the event. The initial decline was very slow and requires a varying energy content in the GRB blast wave over the course of the first hour [3-2].

3-B) Evidence For A Non-Varying Energy Source

The quantity of energy imparted to the relativistic ejecta, E_REL, and the bulk Lorentz factor, Γ, are the two fundamental properties of GRB explosions. The true E_REL depends sensitively on the geometry of the ejecta. If GRB explosions are conical with an opening angle θ_J, the inferred E_REL is appreciably reduced from a spherical explosion. In this case, the afterglow light curve steepens (“breaks”) as a function of time when Γ becomes < 1/θ_J. It was found, for a group of 41 GRBs, that the true luminosity of GRB afterglows, L_XT = f L_XISO, is constant to a factor of 2, where f = [1 – cos (θ_J)] and L_XISO is the luminosity for isotropic emission [3-3].

 

4) Black holes

 

The existence of black holes is a fundamental prediction of general relativity and various means are being used to observe them [4.1]. Ten years of high-resolution astrometric imaging allows to trace two-thirds of the orbit of the star closest to the central black hole of the Milky Way. It has an orbital period of 15.2 years and a pericentric distance of only 17 light hours. The orbit requires a central mass 3.7 x 10⁶ M_� [4.2].

4-A) Jets From Black Holes

Accretion of gas onto black holes is thought to power the relativistic (“superluminal”) jets ejected from active galactic nuclei (AGN), quasars and microquasars. Superluminal features appear and propagate along the jet shortly after sudden decreases in the X-ray fluxes. The X-ray dip is probably caused by the disappearance of the inner accretion disk as it falls past the horizon, while the remainder of the disk section is ejected into the jet, creating the appearance of a superluminal bright spot. Previously seen in microquasars, it has now been seen in AGNs [4.3].

4-B) Squeezed Stars Near Black Holes

The existence of black holes are a fundamental prediction of general relativity. Direct astronomical observational evidence for black holes is being sought, for example, in the behavior of stars close to them. A class of transient sources, called “squeezers”, which are stars caught in highly eccentric orbits around a massive black hole (MBH), has been studied. Their atypical luminosities, ~ 10⁵ L_� (M/M_�), are powered by tidal interactions with the MBH [4-4].

4-C) Magnetic Coupling Of Black Holes To Accretion Disks

Effects of magnetic coupling (MC) of a rotating black hole (BH) with its surrounding accretion disk are very interesting and were recently discussed in detail. It was shown that the electric current on the BH horizon (Blandford-Znajek process) varies with its latitude. The predicted emissivity was consistent with recent XMM – Newton observations [4-5].

4-D) Isolated Black Holes

Nearby isolated, accreting stellar-mass (3-100M_�) black holes have been searched for. Models suggest that such black holes produce emission of synchrotron radiation at visible wavelengths as well as at X-ray wavelengths. From the SDSS (Sloan Digital Sky Survey) data, 150,000 objects have the characteristic visible spectrum of black holes and 87 of these objects are X-ray sources, according to the ROSAT All Sky Survey. From their optical spectra, 32 of the 87 objects them have been shown not to be black holes, leaving 55 possible candidates for black holes [4-6].

4-E) Supermassive Binary Black Holes

Supermassive black hole binaries exist. A supermassive black hole binary was recently found in the radio galaxy 3C66B with an orbital period of 1.05 years [4-7].

4-F) Electrons Not In Thermal Equilibrium Near The Black Hole

The detection of polarized radiation from the center of our galaxy requires a non-thermal electron distribution near the central massive black hole     [4-8]. This argues against the popular ADAF scenario which assumes the advection of a thermal plasma into the black hole.

4-G) The Close Correlation of Black Hole Mass (M_BH), Bulge Mass (M_BU), Bulge Luminosity (L_BU) And The Central Virial Velocity (σ_V)

M_BH is found to be tightly correlated with L_BU, M_BU (R_E σ_V²) and σ_V where R_E is the effective bulge radius [4-9]. This indicates that the formation of the central black hole and the formation of the galactic bulge are closely connected.

4-H) First Quasars (Massive Black Holes) In The Universe

An optically bright quasar is the phase in the evolution of a massive black hole (MBH) when it is acquiring most of its mass. Emission lines in its spectrum can be used to measure the abundance of heavy elements which is found to be approximately solar, even at redshifts > 6 [4-10], indicating appreciable prior stellar formation. Extended Lyman-α emission was observed around a quasar at redshift 4.5, likely because the quasar illuminates surrounding cold (unionized) gas, producing Lyman-α fluorescence [4-11]. The same cold gas probably produced the prior intense star formation. Radio-quiet quasars at redshift ~ 4 show strong thermal dust emission [4-12], also an indication of prior star formation. The first quasars have a characteristic spectral signature, which has been observed [4-13].

 

5) Gravitational Waves

 

Gravitational waves, predicted by general relativity, are now being searched for by the laser gravitational wave interferometers LIGO and VIRGO [5-1]. For these interferometers, compact object merges were shown to be the most promising sources of gravitational waves, in particular, the dominant source was found to be double black hole mergers [5-2]. The coalescence of massive black hole binaries provides a primary source of low-frequency gravitational radiation detectable by LISA (Laser Interferometry Space Antenna) [5-3].

 

6) Plasma Astrophysics

 

The creation, amplification and destruction (reconnection) of magnetic fields are some of the fundamental problems in plasma astrophysics. Magnetic fields are certainly connected with the production of jets and general plasma ejections. However, the nature of this process is not well understood.

6-A) Dynamo Magnetization

An efficient scenario for magnetization of very young galaxies (~ of age 1/2 gigayear) was suggested to be a dynamo driven by cosmic rays. Strong star formation is, however, required for this process [6-1].

6-B) Fast Reconnection

Fast reconnection is very important in many phenomena, but it was recently shown that it is suppressed in weakly ionized plasmas due to ohmic diffusion [6-2].

6-C) Turbulence In Reconnection

Three-dimensional particle simulations of magnetic reconnection reveal the development of turbulence driven by intense electron beams that form near the reconnection region. The turbulence collapses, forming regions where the electron density is depleted (“electron holes”) [6-3].

6-D) Plasma Eruptions

As noted previously, astrophysical plasma eruptions are not well understood. A recent review of our present knowledge of plasma eruptions has recently been made connected with the sun [6-4] which come from the solar corona [6-5] where particle acceleration occurs [6-6].

6-E) Origin Of Intergalatic Magnetic Fields

The energy content of intergalactic magnetic fields is very large. The escape of magnetic fields from galaxies has been suggested but the exact origin of the fields (e.g., supermassive black holes, star bursts, etc.) and how the escape occurs are not clear [6-7]. In clusters of galaxies high magnetic fields extend out to M_pc radii [6-8].

6-F) Creation Of Strong Magnetic Fields In Supernovae

A modest value of the initial rotation of the iron core in a SNII explosion, gives a very rapidly rotating protoneutron star and strong differential rotation of the infalling matter. Saturation fields ~10¹⁵ – 10¹⁶ G develop 300 msec after bounce [6-9].

6-G) Origin Of Jets From Pulsars

A pulsar is a rotating magnetized neutron star [6-10]. Jets have been observed from pulsars, for example, those from the Vela pulsar [6-11]. Does the material of the jets come from an accretion disk or is it electrons-positrons coming from a polarized vacuum?

 

7) The Physics of stars

 

7-A) First Stars

We know that reionization of the universe occurred at redshifts z ~6-20, but exactly what were the first objects that created the necessary ionizing photon background (> 13.9eV) is not known: they could have been massive stars, supernovae or primordial miniquasars (black holes). A comprehensive investigation of the detectability of the first stars and their enrichment signatures needs to be made [7-1].

7-B) Population III Metal-Free Stars

The recently studied star HE 0104-5240 is the most iron-deficient star yet identified, with an iron abundance 1/200,000 that of the Sun. It appears to be a relic of the early universe [7-2].

7-C) Primordial Dust

Large amounts of dust (> 10⁸ M_�) have recently been discovered in high-redshift quasars and galaxies. Primordial supernovae or star bursts are indicated to be the dominant source of this dust [7-3].

7-D) Supernovae Ia

Supernovae Ia (SNIa) were used to detect the observed acceleration of the universe, but the physical process occurring are not well understood. Large-scale, three-dimensional numerical simulations of the deflagration stage of a thermonuclear SNIa explosion show the formation and evolution of a highly convoluted turbulent flame in the gravitational field of an expanding carbon-oxygen white dwarf. There is disagreement, however, between calculations and observations. The disagreement could be partially resolved, perhaps, if the deflagration were to trigger a detonation [7-4].

7-E) Neutron Stars With Large Magnetic Fields

Neutron stars have the densest matter known, with ~1 solar mass inside a sphere of radius 20 kilometers. The density at their centers is greater than nuclear densities and they can have magnetic fields > 10¹⁵ Gauss. The high densities can imply new states of matter (e.g., quark matter) and the large magnetic fields imply effects such as: 1) Vacuum Birefringence (polarized light changes its speed and, hence, its wavelength, depending on the orientation with the magnetic field; 2) Photon Splitting (photons can split (or merge) in fields > 10¹⁴ G); 3) Scattering Suppression (the field can prevent the electron from vibrating); and 4) Atom Distortion (in a 10¹⁴ G field, a hydrogen atom becomes an ellipsoid with a minor radius (^ to B) 200 times smaller than the Bohr radius). Magnetic instabilities in magnetars (neutron stars with magnetic field > 10¹⁵ G) can account for enormous flares of gamma and X-ray radiation [7-5].

7-F) Neutron Stars As Neutrino Sources

An accreting neutron star can be an important source of neutrinos. The magnetospheres of accreting neutron stars develop electrostatic gaps with huge potential drops. Protons and ions, accelerated in these gaps along the dipolar magnetic field lines to energies > 100 TeV, can impact onto the surrounding accretion disk producing neutrinos. The neutrino detector ICECUBE should be able to detect the neutrinos from a source such as H0535+26 which is a Be-/X-ray transient in which the compact object is a 104s pulsar in an eccentric orbit around the BOIII star HDE245770. A smaller detector such as AMANDA could detect the neutrinos by folding the observations with the orbital period [7-6].

7-G) The Maximum Spin Of Neutron Stars

From general relativity, the maximum spin of a neutron star is predicted to be 1,180 Hz [7-7], whereas observations indicate that the maximum spin is 619 Hz [7-8]. The discrepancy might be due to resonances between the spin frequency and orbital precession frequencies at different radial distances in the accretion disk, predicted by general relativity [7-9]. They might also be slowed by the emission of exotic gravitational waves [7-10].

7-H) The Cores Of Neutron Stars

Neutron stars may be our only window on the properties of matter beyond nuclear density, such as cores containing strange matter or a Bose-Einstein condensate of pions. Mass measurements and redshifts can distinguish the various possibilities [7-11].

 

8) THE PHYSICS OF Galaxies

 

8-A) Correlation Of Galaxies

Understanding the correlation distance between galaxies has long been a goal of modern observational cosmology. From the Sloan Digital Sky Survey (SDSS), it was found that red galaxies (similar to elliptical galaxies) have a correlation length of 6.6 h^-1 Mpc, whereas blue galaxies (similar to spiral galaxies) have a correlation length 4.5 h^-1 Mpc [8-1].

8-B) Luminosity Function Of Galaxies

The physical mechanisms that determine the luminosity function of galaxies in hierarchical clustering models have been investigated. Gas cooling, photoionization at high redshifts, feedback processes, galaxy merging and thermal conduction were studied. It was found that the relative paucity of very bright galaxies can only be explained if cooling in massive halos is strongly suppressed [8-2].

8-C) Virial Shocks In Galaxies

The conditions for the existence of a virial shock in the gas falling in a spherical dark matter halo have been investigated. When radiative cooling is efficient, the shock does not form. In particular, it is found that the virial shock does not form for redshifts > 2 and never forms in halos < 3 x 10¹¹M_�. The direct collapse of cold gas (without a virial shock) into a disc has nontrivial effects on star-formation and outflows [8-3].

8-D) Star Formation In Galaxies

Star formation in grand-design spiral galaxies is often attributed to compression from a density wave, even though these galaxies do not have higher star formation rates per unit gas or area then flocculent (short arms and patchy) galaxies. Both types satisfy the same Kennicutt relation between average star formation rate and gas surface density. These observations indicate that small-scale star formation processes are the same everywhere, regardless of the presence (or lack of) a spiral wave. The star formation rate has a Fourier transform power spectrum µ k^β, with β=-1 at large scales (small k) and β=-5/3 at small scales (large k). It has been suggested that star formation is due to turbulence generated by sheared gravitational instabilities [8-4].

8-E) Barred Galaxies

Previous theoretical work has suggested that a bar in a galaxy could be dissolved by the formation of a mass concentration in the center. In an extensive high-quality N-body simulation study, it was found that the central mass has to be as large as several percent of the disk mass to completely destroy the bar [8-5].

8-F) Gas-Stripping Of Galaxies

In the Perseus cluster, gas associated with infalling galaxies may be stripped completely at the outskirts and only compression waves (shocks) may reach the central regions. The passage of such waves can explain the features of the Perseus core. The simulations made show that waves can induce oscillations which can generate temperature “edges” on opposite sides of the central galaxy [8-6].

8-G) Galactic Coronae

Evidence has recently been presented that our galaxy is surrounded by a hot corona [8-7] like that of the sun [6-5].

8-H) Merging Of Galaxies

Observations indicate that an average (L*) galaxy underwent 0.8-1.8 merger events during the redshift interval 0 < z < 1 [8-8].

 

9) VACUUM ENERGY

 

Recent observations indicate the existence of a positive cosmological constant Λ (identified with the vacuum energy), with the magnitude Λ(Gh/2πc³) = ΛL_P² ~ 10^-123. This is 123 orders of magnitude less than the Planck energy scale, when quantum effect become important in gravitation.

9-A) Variation Of Λ With Time

Λ could be dynamical (varying in time), being big at the inflation era and evolve to its “natural” value, zero, at late times. Thus, for example, Λ could be small now because the universe is old. Saying this in the other words,  Λ^-1 has a characteristic distance 10⁺⁶¹Lp. The solution to the problem of the cosmological constant may be connected to the fact that Λ was big when  Λ^-1 was comparable to Lp (the size of the universe near the Planck era) and Λ^-1 is so big today because the universe is so big. To make a viable theory out of the above, we must link the vacuum energy (fluctuations) to the size or age of the universe [9-1].

9-B) Decay Of Λ Into Photons

The corresponding energy density, ρ_Λ, could decay by the emission of photons, for example, as it decreases. Precision measurements, however, show that CMB is thermal to a high precision, indicating that the CMB energy density ρ_R can not change by more than δρ_R/ρ_R ~10^-4 since a redshift z~10⁵ when the interaction between matter and radiation was last strong enough for thermal relaxation. This argues against the decay of Λ into photons [9-1].

9-C) Anthropic Considerations

Anthropic considerations offer a possibility of solving the two separate large cosmological constant problems: 1) Why is it so small today?; and 2) Why did it become important today? [9-2]. Only in such a universe could we exist.

 

10) Casimir Effect In Cosmology

 

A possible source of dark energy is the fluctuation of quantum fields (Casimir Energy) inhabiting extra compactified dimensions.

10-A) Required Dimension To Explain Dark Energy

When the characteristic size of the universe was the Planck length
L_Pl = 1.6x10^-33 cm, the expected quantum vacuum or Casimir energy density was ~ (L_Pl)^-4 = 10¹¹⁸ GeV cm^-3. (The conversion factor of length to energy is hc/2π = 2 x 10^-14 GeV cm.) However, today, we require an energy density 3H₀² /8πG = 1.05 x 10^-5 h₀² GeV cm^-3. We thus need to increase the effective length L_Pl by a factor 10³¹, which implies an effective dimension L ~ 100μ, in order to have the necessary Casimir energy density [10-1].

10-B) Comparison With Calculations

The exact required dimension L of the compactified space is probably uncertain by an order of magnitude. We estimated above the Casimir energy to be ~1/L⁴. In an exact calculation, the Casimir energy of a fermion field on a circle of radius L, was shown to be + 2.02 x 10^-4/L⁴ [10-2], which indicates that in the previous estimates for the Casimir energy, the relation 1/(10L)⁴ perhaps should have been used..

 

11) Dark Matter

 

About 30% of matter acts like cold dark matter (CDM) and is invisible, making its presence felt only by its gravitational interaction. The most popular candidate for CDM is the neutralino, with a mass ~ 1000 GeV/c2, predicted by the theory of supersymmetry [11-1]

11-A) Dark Matter Cusps And Dwarf Galaxies

One of the major problems with the neutralino CDM theory is that numerical simulations predict “cusps” of CDM at the centers of galaxies and clusters of galaxies, which have not been observed. The neutralino CDM theory also predicts ten times more dwarf galaxies than have been observed. Self-interacting dark matter has been suggested to possibly alleviate these problems. However, observations of strong and weak lensing  rule out strongly self-interacting dark matter in clusters of galaxies at a level > 5σ [11-2]. Another problem with this theory is that it was shown that weakly self-interacting dark matter models, which can produce halo cores of the sizes observed in dark-matter-dominated galaxies, are unable to reconcile the number of satellites in the Galactic halo with the observed number of dwarf galaxies in the Local Group [11-2]. Long-slit optical spectra were recently taken of 200 dwarf galaxies. The inner dark matter halo density profiles were obtained from the observed rotation curves. Differing from previous investigations it was concluded that their observations are consistent (and not inconsistent) with the cusps halos predicted by the CDM paradigm [11-4].

11-B) Density Profiles of Dark Matter

N-body simulations recently indicated that the density profiles of dark matter halos are not universal as previously thought, presenting shallower cores in dwarf galaxies and steeper cores in clusters [11-5].

11-C) Dark Matter Annihilation

It has been suggested that the recent detection of 511 keV γ rays [11-6] from the galactic bulge is a consequence of the annihilation of low mass   (~ MeV) particles of dark matter [11-7], which is a mass much lower than the mass of the popular neutralino candidate ~ 10⁶ MeV.

11-D) The Dark Matter Problem In Galaxies

Disks are predicted in numerical calculations to be smaller than those observed. N-body/gasdynamical simulations have been made and it was concluded that revision must be made in the manner in which baryons assemble into galaxies [11-8]. It was suggested that a strong early galactic wind might have caused the inner CDM halo to appreciably expand, after absorbing energy and momentum from the galactic wind [11-9].

 

12) new gravitational physics

 

12-A) Modifying Newtonian Physics

MOND (Modified Newtonian Dynamics) [12-1], a modification of newtonian physics, was recently discussed in a cosmological scenario. It was found that the characteristic acceleration, a₀, of the MOND theory is not really a constant but has a M^1/3 dependence, where M is the source mass [12-2]. The MOND scenario will probably have difficulty to explain the result from galaxy-galaxy gravitational lensing indicating that galactic halos extend much further than can be probed via rotation curves [12-3].

12-B)Modifying General Relativity

It was shown that the observed cosmic acceleration could arise due to a small correction of general relativity. The assumed correction is of the form Rⁿ, where n is not zero and R is the curvature scalar [12-4]. For n < 0, such a correction becomes important in the late universe and leads to accelerating vacuum solutions, providing a purely gravitational alternative to dark energy. When n > 0, this correction explains the early-time inflation epoch. This proposal provides a possible unified and purely gravitational origin for the early and late time acceleration phases of the Universe [12-4].

 

13) Dark Energy

 

13-A) Quintessence

In the basic quintessence scenario, dark energy enters only at late times in order to produce the present cosmic acceleration [13-1]. We might, however, have had a non-negligible quintessence energy density during the recombination (CMB formation) and the structure formation eras. In particular, the ratio of the dark energy to the dark matter at any epoch is a^+3w, where a is the scale factor and w is the average equation of state of the dark energy w=P/ρ. If w=-1 always (such as the vacuum energy), then the dark energy is negligible at the CMB formation era [13-2].

13-B) Time Varying Equation Of State

Dark energy, with a time varying equation of state, could have had an influence on structure formation stretching back to high redshifts [13-3].

13-C) Dark Energy In SDSS Data

Angular cross-correlation between luminous red galaxies from the SDSS (Sloan Digital Sky Survey) and WMAP (CMB) maps have been made. A statistically significant positive correlation, which is consistent with the Late Integrated Sachs-Wolfe Effect due to dark energy, was found [13-4]. This constitutes independent evidence for the existence of dark energy.

13-D) Combining SNIa And CMB To Determine A Time Varying Equation Of State

In order to understand the equation-of-state of dark energy, we need to determine its time dependence. Both SNIa and CMB data are sensitive to w. In CMB data there is a strong degeneracy between Ω_M and w. It was shown that good CMB data, such as that of the Planck Satellite, can significantly improve the ability of a deep SNIa survey to probe w and dw/dz [13-5]. The CMB constrains are nearly orthogonal to those of SNIa in the Ω_M-w plane.

 

14) Varying Fundamental Constants

 

In general relativity, the fundamental constants, such as the velocity of light or the electromagnetic fine structure constant, do not vary in time or space. In modern string theory, however, the coupling constants appearing in the low-energy effective Lagrangian are determined by the vacuum expectation values of some massless scalar field (dilaton). This leads one to expect a correlated variation of all coupling constants [14-1].

14-A) The Variation Of The Fine Structure Constant

Time-variations of the fine structure constant has been claimed to have been observed [14-2]. In order to investigate this time variation at early times, measuring the fine structure constant in the early universe was also suggested [14-3].

14-B) Variation Of The Speed Of Light

Instead of inflation theory, a varying speed of light was suggested to solve the horizon, flatness as well as the cosmological constant problems [14-4].

 

15) Topology

 

15-A) Circles In The Sky

We may be living in a finite universe which is repeated many times. One of the best ways to investigate this hypothesis is to study the CMB WMAP data. A suggested explanation for WMAP temperature correlations, which vanish for angles > 60º, is that we live in a dodecahedral universe with Ω₀=1.013 [15-1]. In this model, the inner radius is 82% of the horizon and the outer radius is 3% greater than the horizon. The horizon sphere self-interacts in six pairs of circles on the sky of angular radius 35º that could, in principle, be detectable [15-1]. Circles on the sky with similar temperature patterns have been searched for. However, no such circles were found for angles > 25º [15-2].

15-B) Wavelets

A spherical Mexican-hat wavelet decomposition of the CMB fluctuations was used to search for evidence of a finite Universe. Compact flat finite topologies were investigated [15-3]. Topological sizes from half to twice the horizon size were considered. Finite topologies with appropriate sizes were found to be as consistent with the CMB data as is an infinite Universe [15-3].

 

16) EXTRA DIMENSIONS

 

In extra dimension theories, ordinary matter is trapped in a three-dimensional surface, called a “brane”, which is embedded in a higher dimensional space called the “bulk”, where only gravity can propagate. In the presence of large extra dimensions (LED) the observed weakness of gravity is a consequence of its “leakage” into the extra dimensions. Collisions with center-of-mass energies (CME) larger than the fundamental gravitational scale (FGS) (which could be the electroweak scale E_EW ~ 1 TeV) can produce gravitons, black holes and branes. Cosmic rays with CME >> TeV, for example, could produce transient black holes (i.e., black holes of very small mass which would evaporate rapidly.

16-A) Early Universe

In cosmology, when the universe was above a temperature of several TeV, stable branes could have been produced, which might be the dark matter observed today [16-1].

16-B) Stellar Interiors

Graviton production in stellar interiors can act as an additional source of cooling. The pulsating white dwarf, G117-B15A, was studied for which the secular rate of the increase of the period of its fundamental mode was measured. For two extra spatial dimensions, it was found that FGS > 8.03 TeV [16-2].

16-C) Modification Of The Friedmann Equation

It was shown that an additional term (1-Ω_M) (H^α /H₀^α-2) arises in the Friedmann equation in theories with extra dimensions [16-3]. The quantity r_C is a crossover scale, beyond which the laws of 4-D gravity break down and become 5-dimensional. The crossover scale is given by
r_C = (1-Ω_M)^{1/(α -2)} H₀^-1 [16-4]. The Friedmann equation can be written in the form (H/H₀)² = Ω_M (1+z)³ + (1-Ω_M) (H/H₀)^α. It was shown [16-4] that:
1) α, in general, is less than unity ; 2) An effective equation-of-state exists:
w_eff = -1 + (α/2) for 10⁴ > z >>1, w_eff = -1+2α/3 for z >> 10^4, and   
w_eff = -1in the distant future; 3) dw/dz ~ 0.2 for z ~ 0.5, where the maximal rate of change of w_eff occurs ; and 4) In the range 0 < z <2, we have w_eff ~ -1 + 0.3α.

16-D) A Stable Scalar In Extra Dimensions

In a large class of extra dimension models, a scalar degree of freedom, called the radion, is long-lived or stable. If M_C is the compactification scale and M_I = V_I^1/4 is the scale of the inflaton potential, then if M_C/M_I is in the range 1 to 10³ and 1 TeV < M_C < 10⁶ TeV, radions could be the dark matter of the universe [16-5]. If M_C ~ 1 TeV, then M_I < 1 TeV, and the inflaton potential is not dominant.

16-E) Perturbation Spectrum

It was shown that the cosmological perturbations generated during inflation are a powerful tool with which to probe the physics of extra dimensions [16-6]. Whereas the scalar cosmological perturbations are unchanged due to a fifth dimension, the spectrum of gravitational waves is affected. The gravitational wave spectrum is changed by a factor proportional to the dimensionless quantity (HL)², where H is the Hubble expansion parameter during inflation and L is the size of the extra dimension [16-6].

16-F) Ekpyrotic/Cyclic Model

It is interesting that the ekpyrotic/cyclic model, based on a brane cosmology, predicts a spectral tilt n_S ~0.95, similar to inflation models   [16-7]. However, whereas inflation models predict a tensor to scalar contribution to the low l multipoles of CMB ~20%, the ekpyrotic/cyclic model predicts a zero tensor contribution [16-7].

 

17) Unifying Dark Energy With Dark Matter

 

17-A) Generalized Chaplygin Gas

Dark energy and dark matter may be due to a new equation of state called quartessence or a generalized Chaplygin gas (GCG) P_X = -A(ρ_x)^-α (α=1 for a Chaplygin gas), where P_X is the pressure and ρ_X is the density. A GCG was compared with WMAP and SNI data. It was found that α is in the range 0 < α < 0.2, which is much different from α = 1 value of the Chaplygin gas [17-1].

17-B) Interaction Of Dark Energy With Dark Matter

Masses are due to the interaction of fields. It was suggested that dark matter could have masses depending on the scalar field associated with the dark energy [17-2]. Assuming a dark energy-dark matter interaction, the ratio of the dark energy-dark matter interaction energy to the gravitational interaction energy might be able to be determined to an accuracy of ~5% in an ideal CMB experiment [17-3].

 

18) Cosmic Microwave Background (CMB)

 

The CMB is probably the most powerful tool to study cosmology theory [18-1]. The basic “Big Bang” cosmology theory assumes that the previous existence of a superluminal (v > c) inflationary epoch, solves the homogeneity and isotropy problems of the universe as well as creating the density perturbation spectrum observed.

18-A) WMAP Data And Inflation Theory

The impressive result of the WMAP CMB data is the fact that the data confirm the basic predictions of inflation theory. Most impressive, perhaps, is the temperature-polarization result. In the CMB data, large angles (l < 150) are greater than the horizon. Thus, fluctuations for l < 150 can most easily can be explained by a superluminal (v > c) inflation theory. These fluctuations were observed by WMAP [18-2]. The inflation theory further predicts an anti correlation of temperature and polarization fluctuations, with a negative correlation peak at l ~ 150. This was also observed [18-2]. The inflation theory predicts an approximate flat universe (little curvature), an approximate scale-invariant spectrum, with gaussian fluctuations, all observed by WMAP [18-1]. The WMAP data were also able to eliminate a popular inflation model, a potential that is proportional to the fourth power of the scalar (inflaton) field [18-2].

18-B) Initial Einstein Static State

Recently, a universe which started from an initial Einstein static state, large enough to avoid the Planck quantum gravity regime, was studied with the predicted results in agreement with WMAP observations [18-3].

18-C) De Sitter Universe

A spatially closed Universe of de Sitter type, which starts from a finite radius and predicts the low-l fall-off of the WMAP spectrum, was studied [18-4].

18-D) WMAP Data and SDSS

Cosmological parameters were investigated using the 3-D power spectrum from 200,000 galaxies in the SDSS data in combination with WMAP data [18-5]. Their results are consistent with the simple cosmological model: 1) spectral tilt n_S = 1, 2) dn_S/dlnk = 0; 3) the ratio of tensor to scalar fluctuations is zero; and 4) zero mass neutrinos [18-5].

18-E) Alignment Of The Quadropole With The Octopole

It was shown that the alignment between the quadropole and octopole in the WMAP data has a probability of 1 in 60 to occur [18-6]. The alignment is in the direction of the nearest cluster of galaxies, the Virgo group. This may indicate that the alignment could be a local effect.

 

19) Inflation and the Formation of structures in the universe

 

At present, the basic theory of cosmology is inflation theory [19-1].

The formation of structures is sensitive to the potential V(φ) of the scalar field φ (the inflaton) N (~50) e-folds before the end of the exponential inflation expansion period. The observed WMAP parameters are, thus, related to the potential V(φ_N) to the first derivitive of the potential V(φ_N)/dφ=V’(φ_N), second derivative V’’ and the third derivative V’’’.

 19-A) Relation Of Inflation Parameters And Observed Parameters

The following dimensionless combinations can be used: ε = (M_Pl/2)(V’/V)2, η=(M_Pl²/2)(V’’/V) and ξ=M_Pl⁴(V’V’’’/V²), with ε, η and ξ << 1 for inflation to occur. Some interesting observed parameters are n_S, (the power of the power-law spectrum  of the density perturbations, where λ= 2π/k is the size of the perturbation), n_T (the power of the power-law spectrum of the gravitational wave spectrum) and r (the ratio of the tensor (gravitational wave) to the scalar (density fluctuation spectrum) quadropole contribution to the CMB spectrum). The relations between n_T, n_S, dn_S/dlnk and r with ε, η and ξ are: r=16ε, n_S=1-6ε+2η, n_T=-2ε and dn_S/dlnk=-16εη+24ε²+2ξ. For the simple potential V(φ)=λ φ ²/4, N=50 and φ_N=20 M_Pl, we have n_S = 0.94, r=0.3 and dn_S/dlnk ~ 0. WMAP and other CMB observations, in conjunction with the 2dFGRS galaxy distribution and Lyman-alpha data found that n_S (at k₀ = 0.002 Mpc^-1) = 1.10, dn_S/dln k = -0.042 and r < 0.71 [18-2].

19-B) Types of Inflation Models

The various types of inflation models can be separated into: A) Small field (η<0)(0<ε); B) Large field (0<η)(η<ε); and C) Hybrid models (0<ε) (ε<η). The A and B models predict n_S<1. The C model can have n_S>1. For n_S=0.85, for example, r<0.3 in the A model, 0.3 < r <1 in the B model, and r > 1 in the C model [19-2].

19-C) Examples Of Inflation Models

Examples of the A model are: potentials of spontaneous symmetry-breaking (e.g., New Inflation) [19-3], giving r ~ 0.06 for n_S=0.98 and spontaneously broken supersymmetry [19-4], giving r ~ 0.016 for n_S=0.98. An example of the B model is chaotic inflation [19-5], giving r ~ 0.3 for n_S=0.96. Model C arises in hybrid inflation [19-4] [19-6]. In this model, besides the field φ, there is a second field σ. The second field enters only to make the potential V(φ) = 0 for φ above a critical value. Inflation can essentially be studied in function only of φ only.

19-D) Adiabatic And Isocurvature Fluctuations

The WMAP data is consistent with adiabatic fluctuations [18-2]. This is the prediction of single field inflation models. Multiple particle inflation models predict the creation of isocurvature perturbations due to the generation of entropy. WMAP data indicate that the ratio of isocurvature to adiabatic perturbations is < 33 % [18-2].

19-E) Gaussian Fluctuations

A smooth inflaton potential generates Gaussian fluctuations. Sharp features in the inflaton potential can generate non-gaussian fluctuations [19-7]. Supergravity models create steps in the inflaton potential as a consequence of successive spontaneous symmetry-breaking phase transitions of fields coupled to the inflaton [19-8]. The WMAP data is consistent with pure gaussian fluctuations [18-2].

19-F) A Spherical Universe

The WMAP data gives Ω₀=1.02±0.02, indicating that Ω₀ may be greater than unity (i.e. a spherical universe) [19-9]. (Ω₀-1)=1/(a²H²) was driven towards zero exponentially during inflation, but was necessarily dominant at early times. Ω₀>1 enhanced curvature in the past, creating a turn-around point, which implies a maximum number of e-folds in the inflation period. For Ω₀-1=1.02, the maximum number of e-folds is ~ 64. In general, we assume that φ and V were large at the beginning of inflation, implying that δρ/ρ ~ δT/T~1, which, however, is not observed [19-9].

19-G) Fast Inflation Rolling Stage

In order to explain the indicated small power on the largest angular scales of the WMAP data, a fast rolling stage in the evolution of the inflaton field at the beginning of the last ~65 e-folds of inflation was suggested [19-10].

19-H) Density Fluctuations Created In The Reheating  Era

In the reheating epoch, the inflaton couples to ordenary matter. Generally, these particles are light and their fluctuations lead to density perturbations [19-10]. The relation between the slope of the spectrum of the produced density perturbations and the potential of the inflaton field is different from the standard relations. A much smaller level of gravitational waves is predicted in this scenario [19-11].

 

SUMMARY OF SOME OF THE BIG QUESTIONS

 

1) COSMIC RAYS

Can UHECR be produced by:

·       astrophysical  shocks?

·       Wimpzillas?

·       GRBs?

·       Magnetars?

2) NEUTRINO PHYSICS

·        What solar physics can be studied with solar neutrinos?

·        What are the neutrino sources for AMANDA and other high energy neutrino detectors?

3) GRBs

·        Is the energy source varying?

4) BHs

Can we observe:

·        squeezers?

·        the magnetic coupling of the BH to the accretion disk?

·        the electron distribution near the BH?

5) GRAVITATIONAL WAVES

·        Assuming that BH solar mass mergers are the primary source for LIGO and VIRGO, and massive BH mergers the primary source for LISA, can understanding better the merging process improve the detecting efficiency?

6) PLASMA ASTROPYSICS

What is the physical origin of:

·        astrophysical magnetic fields?

·        plasma eruptions and jets?

7) THE PHYSICS OF STARS

·        What were the first objects?

·        Why is the maximum spin of neutron stars so low?

·        Can the large potential drop in magnetospheres of neutron stars be detected?

·        Can we define the equation of state in the core of neutron stars from existing observations?

8) THE PHYSICS OF GALAXIES

·        Why are there so few bright galaxies?

·        When a virial shock does not exist, how are galactic star formation and galactic outflows affected?

·        What is the turbulence-star formation connection?

·        What is the bar-central mass connection?

·        How is a hot galactic corona created?

9) VACUUM ENERGY

·        Is the decay of the vacuum energy into particles consistent with observations?

10) CASIMIR EFFECT IN COSMOLOGY

·        Can the spatial variation of the vacuum energy of the Casimir effect be observed?

11) DARK MATTER

·        Do dark matter cusps exist in galaxies and clusters of galaxies?

·        How do baryons cluster into the dark matter halos to form galaxies?

·        Why are observed disks bigger than calculations predict?

·        Are the many small dark matter halos without baryons?

12) NEW GRAVITATIONAL PHYSICS

·        Does existing observational data indicate that a₀ of MOND varies with the mass and redshift of the object?

·        Can a modified GR theory explain existing observational data?

13) DARK ENERGY

·        Can CMB and SNIa data alone determine dw/dz in a quintessence model and differentiate pure quintessence from other suggested models (e.g. Generalized Chaplygin Gas, Extra Dimensions, Dark Energy – Dark Matter coupling)?

14) VARYING FUNDAMENTAL CONSTANTS

·        Can the variation of the speed of light substitute inflation theory?

·        To what extent can the fine structure constant vary and be consistent with all known cosmological-astrophysical data?

15) TOPOLOGY

·        What are all the observational means to study the topology of the universe?

16) EXTRA DIMENSIONS

·        What are the observational means to differentiate a theory of extra dimension explaining dark energy from other existing theories (e.g., quintessence, generalized Chaplygin gas)?

17) UNIFYING DARK ENERGY AND DARK MATTER

·        Can observational data differentiate this model from other models?

18) CMB

·        What is the best way to explain the low quadropole and octopole, their alignment, and their alignment pointing to the Virgo group?

19) INFLATION AND THE FORMATION OF STRUCTURES IN THE UNIVERSE

·        Can existing cosmological data limit the possible inflation model?

 

---

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