Cosmic Background Explorer Research Articles

Infrared measurements from the Cosmic Background Explorer (COBE)

The Cosmic Background Explorer (COBE) satellite was developed by NASA's Goddard Space Flight Center to measure the diffuse IR and microwave radiation from the early universe, to the limits set by our astrophysical environment. It was launched 18 November 1989 and carried three instruments, a FIR Absolute Spectrophotometer (FIRAS) to compare the cosmic microwave background radiation with a precise blackbody, a Differential Microwave Radiometer (DMR) to map the cosmic radiation precisely, and a Diffuse Infrared Background Experiment (DIRBE) to search for the accumulated light of primeval galaxies. The cosmic microwave background radiation spectrum was measured 1000 times more precisely than was possible before the COBE launch. The microwave background was found to have an intrinsic anisotropy for the first time, at a level of a part in 10 5 with a smoothing of 10°. A comprehensive set of absolutely calibrated IR sky maps has been acquired to search for the cosmic IR background.

On the anisotropy of the cosmic microwave background

view Abstract Citations (17) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Anisotropy of the Cosmic Microwave Background Meszaros, A. Abstract It is likely that the anisotropy of the cosmic microwave background- discovered by the COBE satellite is due to near structures (voids, superclusters, etc., at redshift <2) and has nothing in common with the distribution of matter at redshift ~1000. This result follows from the analytic calculation of the redshift of light that crosses a spherical void. Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/173786 Bibcode: 1994ApJ...423...19M Keywords: Anisotropy; Background Radiation; Cosmic Rays; Cosmology; Microwave Emission; Universe; Baryons; Cosmic Background Explorer Satellite; Mass Distribution; Photons; Red Shift; Symmetry; Astrophysics; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; COSMOLOGY: THEORY full text sources ADS |

The Local Supercluster as a test of cosmological models

The Local Supercluster kinematic properties (the Local Group infall toward the Virgo Cluster and galaxy density distribution about the Virgo Cluster) in various cosmological models are examined utilizing large-scale N-body (PM) simulations 500(exp 3) cells, 250(exp 3) particles, and box size of 400 h(exp -1) Mpc) and are compared to observations. Five models are investigated: (1) the standard, Cosmic Background Explorer Satellite (COBE)-normalized cold dark matter (CDM) model with omega = 1, h = 0.5, and sigma(sub 8) = 1.05; (2) the standard Hot Dark Matter (HDM) model with omega = 1, h = 0.75, and sigma(sub 8) = 1; (3) the tilted CDM model with omega = 1, h = 0.5, n = 0.7, and sigma(sub 8) = 0.5; (4) a CDM + lambda model with omega = 0.3, lambda = 0.7, h = 2/3, and sigma(sub 8) = 2/3; (5) the PBI model with omega = 0.2, h = 0.8, x = 0.1, m = -0.5, and sigma(sub 8) = 0.9. Comparison of the five models with the presently available observational measurements v(sub LG) = 85 - 305 km/s (with mean of 250 km/s), delta(n(sub g))/(n(sub g)-bar) = 1.40 + or - 0.35) suggests that an open universe with omega approximately 0.5 (with or without lambda) and sigma(sub 8) approximately 0.8 is preferred, with omega = 0.3-1.0 (with or without lambda) and sigma(sub 8) = 0.7-1.0 being the acceptable range. At variance with some previous claims based on either direct N-body or spherical nonlinear approaches, we find that a flat model with sigma(sub 8) approximately 0.7-1.0 seems to be reasonably consistent with observations. However, if one favors the low limit of v(sub LG) = 85 km/s, then an omega approximately 0.2-0.3 universe seems to provide a better fit, and flat (omega = 1) models are ruled out at approximately 95% confidence level. On the other hand, if the high limit of v(sub LG) = 350 km/s is closer to the truth, then it appears that omega approximately 0.7-0.8 is more consistent. This test is insensitive to the shape of the power spectrum, but rather sensitive to the normalization of the perturbation amplitude on the relevant scale (e.g., sigma(sub 8)) and omega. We find that neither linear nor nonlinear relations (with spherical symmetry) are good approximations for the relation between radial peculiar velocity and density perturbation, i.e., nonspherical effects and gravitational tidal field are important. The derived omega using either of the two relations is underestimated. In some cases, this error is as large as a factor of 2-4.

Strong gravitational lensing statistics as a test of cosmogonic scenarios

Gravitational lensing statistics can provide a direct and powerful test of cosmic structure formation theories. Since lensing tests, directly, the magnitude of the nonlinear mass density fluctuations on lines of sight to distant objects, no issues of 'bias' (of mass fluctuations with respect to galaxy density fluctuations) exist here, although lensing observations provide their own ambiguities of interpretation. We develop numerical techniques for generating model density distributions with the very large spatial dynamic range required by lensing considerations and for identifying regions of the simulations capable of multiple image lensing in a conservative and computationally efficient way that should be accurate for splittings significantly larger than 3 seconds. Applying these techniques to existing standard Cold dark matter (CDM) (Omega = 1) and Primeval Baryon Isocurvature (PBI) (Omega = 0.2) simulations (normalized to the Cosmic Background Explorer Satellite (COBE) amplitude), we find that the CDM model predicts large splitting (greater than 8 seconds) lensing events roughly an order-of-magnitude more frequently than the PBI model. Under the reasonable but idealized assumption that lensing structrues can be modeled as singular isothermal spheres (SIS), the predictions can be directly compared to observations of lensing events in quasar samples. Several large splitting (Delta Theta is greater than 8 seconds) cases are predicted in the standard CDM model (the exact number being dependent on the treatment of amplification bias), whereas none is observed. In a formal sense, the comparison excludes the CDM model at high confidence (essentially for the same reason that CDM predicts excessive small-scale cosmic velocity dispersions.) A very rough assessment of low-density but flat CDM model (Omega = 0.3, Lambda/3H(sup 2 sub 0) = 0.7) indicates a far lower and probably acceptable level of lensing. The PBI model is consistent with, but not strongly tested by, the available lensing data, and other open models would presumably do as well as PBI. These preliminary conclusions and the assumptions on which they are based can be tested and the analysis can be applied to other cosmogonic models by straightforward extension of the work presented here.

Cosmic microwave background anisotropies in cold dark matter models with cosmological constant: The intermediate versus large angular scales

We obtain predictions for cosmic microwave background anisotropies at angular scales near 1 deg in the context of cold dark matter models with a nonzero cosmological constant, normalized to the Cosmic Background Explorer (COBE) Differential Microwave Radiometer (DMR) detection. The results are compared to those computed in the matter-dominated models. We show that the coherence length of the Cosmic Microwave Background (CMB) anisotropy is almost insensitive to cosmological parameters, and the rms amplitude of the anisotropy increases moderately with decreasing total matter density, while being most sensitive to the baryon abundance. We apply these results in the statistical analysis of the published data from the UCSB South Pole (SP) experiment (Gaier et al. 1992; Schuster et al. 1993). We reject most of the Cold Dark Matter (CDM)-Lambda models at the 95% confidence level when both SP scans are simulated together (although the combined data set renders less stringent limits than the Gaier et al. data alone). However, the Schuster et al. data considered alone as well as the results of some other recent experiments (MAX, MSAM, Saskatoon), suggest that typical temperature fluctuations on degree scales may be larger than is indicated by the Gaier et al. scan. If so, CDM-Lambda models may indeed provide, from a point of view of CMB anisotropies, an acceptable alternative to flat CDM models.

The phenomenological status of late time phase transition models after cosmic background radiation anisotropy measurements

Some relatively model-independent results for structure formation via late time phase transitions (LTPT) are discussed. In particular, generic LTPT power spectra are presented. The implication of the recent Cosmic Background Explorer (COBE) detection of the cosmic background radiation (CBR) anisotropy at large angular scales (greater than or approximately equal to 7 deg) and the tight upper limits from small angular scales (approximately 1 deg) to LTPT models are discussed. Special attention is focused on the observational constraints and possible non-Gaussian signatures of CBR temperature anisotropies from LTPT and other non-Gaussian models. It is shown that while LTPT have been seriously constrained by the recent data, viable models do remain which provide more power on the 100-200 Mpc scales than do more traditional primordial Gaussian density fluctuation models. Tests for such models are presented, including possible anisotropies on angular scales less than 8 min.

Cosmic structure formation and microwave anisotropies from global field ordering.

Spontaneous breaking of global symmetries and the consequent field ordering provide a mechanism for the formation of structure in the Universe. We compare the predictions of these theories with the cosmic microwave background (CMB) anisotropy recently detected by the Cosmic Background Explorer (COBE) and with recent observations of large-scale structure. In this paper we give a self-contained discussion of the analytical formalism, and numerical techniques required to simulate the texture, global monopole, global string, and nontopological texture scenarios. The Universe is assumed to have critical density and to be dominated by "cold" dark matter. Our main conclusions are that all of these scenarios are consistent with the reported amplitude, statistical properties, and multipole spectrum of the COBE signal, for a high bias factor $b\ensuremath{\sim}(2\ifmmode\pm\else\textpm\fi{}1){h}^{\ensuremath{-}1}$. The distinctive non-Gaussian character of the CMB anisotropies produced in these theories is investigated, and the prospects for its detection are discussed. We also compare the theories with the recent data on the large-scale galaxy distribution. Like the "standard" inflationary scenarios, if $\ensuremath{\Omega}=1$, $\ensuremath{\Lambda}=0$, these theories may have insufficient power on large scales.

Calibration of the COBE FIRAS instrument

view Abstract Citations (76) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Calibration of the COBE FIRAS Instrument Fixsen, D. J. ; Cheng, E. S. ; Cottingham, D. A. ; Eplee, R. E., Jr. ; Hewagama, T. ; Isaacman, R. B. ; Jensen, K. A. ; Mather, J. C. ; Massa, D. L. ; Meyer, S. S. ; Noerdlinger, P. D. ; Read, S. M. ; Rosen, L. P. ; Shafer, R. A. ; Trenholme, A. R. ; Weiss, R. ; Bennett, C. L. ; Boggess, N. W. ; Wilkinson, D. T. ; Wright, E. L. Abstract The FIRAS instrument on the COBE satellite was designed to accurately measure the spectrum of the cosmic microwave background radiation (CMBR) in the frequency range 1-95 cm^-1^ with an angular resolution of 7^deg^. We describe the calibration of this instrument, including the method of obtaining calibration data, reduction of data, the instrument model, fitting the model to the calibration data, and application of the resulting model solution to sky observations. The instrument model fits well for calibration data that resemble sky conditions. The method of propagating detector noise through the calibration process to yield a covariance matrix of the calibrated sky data is described. The final uncertainties are variable both in frequency and position, but for a typical calibrated sky 2.6^deg^ square pixel and 0.7 cm^-1^ spectral element the random detector noise limit is of order of a few times 10^-7^ ergs cm^-2^ s^-1^ sr^-1^ cm for 2-20 cm^-1^, and the difference between the sky and the best-fit cosmic blackbody can be measured with a gain uncertainty of less than 3%. Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/173577 Bibcode: 1994ApJ...420..457F Keywords: Background Radiation; Calibrating; Cosmic Background Explorer Satellite; Mathematical Models; Michelson Interferometers; Angular Resolution; Data Reduction; Error Analysis; Fourier Transformation; Pixels; Signal Processing; Signal To Noise Ratios; Astrophysics; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; INSTRUMENTATION: SPECTROGRAPHS full text sources ADS |

Comments on the statistical analysis of excess variance in the COBE differential microwave radiometer maps

view Abstract Citations (116) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Comments on the Statistical Analysis of Excess Variance in the COBE Differential Microwave Radiometer Maps Wright, E. L. ; Smoot, G. F. ; Kogut, A. ; Hinshaw, G. ; Tenorio, L. ; Lineweaver, C. ; Bennett, C. L. ; Lubin, P. M. Abstract Cosmic anisotropy produces an excess variance σ_sky_^2^ in the {DELTA}T maps produced by the Differential Microwave Radiometer (DMR) on CO8E that is over and above the instrument noise. After smoothing to an effective resolution of 10^deg^, this excess, σ_sky_(10^deg^), provides an estimate for the amplitude of the primordial density perturbation power spectrum with a cosmic uncertainty of only 12%. We employ detailed Monte Carlo techniques to express the amplitude derived from this statistic in terms of the universal rms quadrupole amplitude, <Q_RMS_^2^>^0.5^. The effects of monopole and dipole subtraction and the non-Gaussian shape of the DMR beam cause the derived <Q_RMS_^2^>^0.5^ to be 5%-10% larger than would be derived using simplified analytic approximations. We also investigate the properties of two other map statistics: the actual quadrupole and the Boughn-Cottingham statistic. Both the σ_sky_(10^deg^) statistic and the Boughn-Cottingham statistic are consistent with the <Q_RMS_^2^>^0.5^ = 17 +/- 5 microK reported by Smoot et al. (1992) and Wright et al. (1992). Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/173537 Bibcode: 1994ApJ...420....1W Keywords: Microwave Radiometers; Monte Carlo Method; Signal To Noise Ratios; Sky Surveys (Astronomy); Variance (Statistics); Anisotropy; Cosmic Background Explorer Satellite; Cosmology; Data Smoothing; Power Spectra; Quadrupoles; Astrophysics; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: OBSERVATIONS full text sources ADS |

Microwave background fluctuations due to the Sunyaev-Zel'dovich effects in pancakes

We calculate distortions in the microwave background radiation from the Sunyaev-Zel'dovich effect, produced by hot gas in large (approximately 100 Mpc) pancakes. The large-scale distribution of the pancakes is taken to be that of a Voronoi foam. Fluctuations for this scenario are estimated to be on the order of delta T/T is approximately 10(exp -5). Using computer simulations, we produce several 32 deg x 32 deg images with 0.25 deg resolution. These images show characteristic linear features produced when a pancake is viewed nearly edge-on. By calculating the two-point and the degenerate three-point correlation functions, we are able to statistically detect such non-Gaussian features even in the presence of a relatively large amount of Gaussian noise. The degenerate three-point correlation function is found to be particularly useful since it is insensitive to correlated Gaussian noise. We also smooth our data over a 7 deg Full Width at Half Maximum (FWHM) Gaussian window to simulate the Cosmic Background Explorer Satellite (COBE) observations. We find that under such low-resolution conditions, the features are highly suppressed.

Measurement of the cosmic microwave background spectrum by the COBE FIRAS instrument

The cosmic microwave background radiation (CMBR) has a blackbody spectrum within 3.4 x 10(exp -8) ergs/sq cm/s/sr cm over the frequency range from 2 to 20/cm (5-0.5 mm). These measurements, derived from the Far-Infrared Absolute Spectrophotomer (FIRAS) instrument on the Cosmic Background Explorer (COBE) satellite, imply stringent limits on energy release in the early universe after t approximately 1 year and redshift z approximately 3 x 10(exp 6). The deviations are less than 0.30% of the peak brightness, with an rms value of 0.01%, and the dimensionless cosmological distortion parameters are limited to the absolute value of y is less than 2.5 x 10(exp -5) and the absolute value of mu is less than 3.3 x 10(exp -4) (95% confidence level). The temperature of the CMBR is 2.726 +/- 0.010 K (95% confidence level systematic).

Parameters of the ultrastable expansive nondecelerative universe

The measurement of the temperature of the cosmic microwave background radiation (CMBR) with the Far InfraRed Absolute Spectrophotometer (FIRAS) on the Cosmic Background Explorer (COBE) satellite gives a possibility for determination of all mutually related parameters of the ultrastable expansive nondecelerative Universe (ENU) with deviations smaller than 0.4%.

Cosmic microwave background dipole spectrum measured by the COBE FIRAS instrument

The Far-Infrared Absolute Spectrophotometer (FIRAS) instrument on the Cosmic Background Explorer (COBE) has determined the dipole spectrum of the cosmic microwave background radiation (CMBR) from 2 to 20/cm. For each frequency the signal is decomposed by fitting to a monopole, a dipole, and a Galactic template for approximately 60% of the sky. The overall dipole spectrum fits the derivative of a Planck function with an amplitude of 3.343 +/- 0.016 mK (95% confidence level), a temperature of 2.714 +/- 0.022 K (95% confidence level), and an rms deviation of 6 x 10(exp -9) ergs/sq cm/s/sr cm limited by a detector and cosmic-ray noise. The monopole temperature is consistent with that determined by direct measurement in the accompanying article by Mather et al.

Power-spectrum-independent constraints on cosmological models

view Abstract Citations (12) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Power-Spectrum--independent Constraints on Cosmological Models Tegmark, Max ; Bunn, Emory F. ; Hu, Wayne Abstract A formalism is presented that allows cosmological experiments to be tested for consistency, and allows a simple frequentist interpretation of the resulting significance levels. As an example of an application, this formalism is used to place constraints on bulk flows of galaxies using the results of the microwave background anisotropy experiments COBE and SP91, and a few simplifying approximations about the experimental window functions. It is found that if taken at face value, with the quoted errors, the recent detection by Lauer and Postman of a bulk flow of 689 km/s on scales of 150$h^{-1}$Mpc is inconsistent with SP91 at a 95\% confidence level within the framework of a Cold Dark Matter (CDM) model. The same consistency test is also used to place constraints that are completely model-independent, in the sense that they hold for any power spectrum whatsoever --- the only assumption being that the random fields are Gaussian. It is shown that the resulting infinite-dimensional optimization problem reduces to a set of coupled non-linear equations that can readily be solved numerically. Applying this technique to the above-mentioned example, we find that the Lauer and Postman result is inconsistent with SP91 even if no assumptions whatsoever are made about the power spectrum. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/174699 arXiv: arXiv:astro-ph/9311053 Bibcode: 1994ApJ...434....1T Keywords: Anisotropy; Astronomical Models; Cosmology; Dark Matter; Microwave Spectra; Power Spectra; Background Radiation; Cosmic Background Explorer Satellite; Entropy; Galaxies; Monte Carlo Method; Nonlinear Equations; Probability Distribution Functions; Physics (General); COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: DARK MATTER; COSMOLOGY: THEORY; Astrophysics E-Print: 18 pages, Plain TeX (4 figures in accompanying file). CfPA 93-th-40, submitted to Ap.J., significantly revised version full text sources arXiv | ADS |

Mixed dark matter from neutrino lasing

view Abstract Citations (16) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Mixed Dark Matter from Neutrino Lasing Starkman, G. D. ; Kaiser, N. ; Malaney, R. A. Abstract We investigate the production of dark matter with non-standard momentum distributions arising from the decay of a relativistic massive neutrino into a lighter fermion and boson H$\rightarrow$F$+$B. We develop the Boltzmann equations for this process, paying particular attention to spin polarisation effects. Such decays can, under certain circumstances, lead to a process of runaway stimulated decays or `neutrino-lasing' resulting, for suitable boson mass, in the production of mixed-dark-matter. We discuss a number of variations on the model; we show how the yield of cold particles can be increased by a simple modification to our original proposal. We discuss the singlet-majoron model as a possible framework for these decays. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/174700 arXiv: arXiv:astro-ph/9312020 Bibcode: 1994ApJ...434...12S Keywords: Boltzmann Transport Equation; Dark Matter; Lasing; Momentum; Neutrinos; Polarization (Spin Alignment); Astronomical Models; Bosons; Cosmic Background Explorer Satellite; Fermions; Nuclear Fusion; Universe; Astronomy; COSMOLOGY: DARK MATTER; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; ELEMENTARY PARTICLES; Astrophysics; High Energy Physics - Phenomenology E-Print: 23 pages, latex, CITA/93/49, available by anon ftp from ftp.cita.utoronto.ca in /cita/nick/neutrinolasing2.ps full text sources arXiv | ADS |

Implications of the millimeter-wave anisotropy experiment for cold dark matter models.

We analyze the Gamma Ursae Minoris (GUM) and Mu Pegasii scans of the millimeter-wave anisotropy experiment in the context of cold dark matter (CDM) models of structure formation, paying particular attention to the two-dimensional nature of the GUM scan. If all of the structure in the (foreground subtracted) data is attributed to cosmic microwave background anisotropy, then there is a detection in each scan. For a standard CDM model, the amplitudes of the signals are individually compatable with the Cosmic Background Explorer measurement, but marginally inconsistent with each other.

COBE DMR observations of the early Universe

The Cosmic Background Explorer (COBE) satellite Differential Microwave Radiometer (DMR) instrument has recently reported the observations of very large scale structure in the microwave sky. The microwave sky as a whole is remarkably uniform in the millimeter to centimeter wavelength range. However, there are variations at a level <or=10-5. The natural interpretation of these variations is as the imprint of spatial curvature fluctuations in the early universe. The implications for gravitation and gravitational instability theories of structure formation are discussed along with a review of the experiment. The results are generally supportive of gravitational instability theories and inflationary/quantum cosmology models. Failure to find fluctuations within a factor of two of the COBE DMR level would have contradicted gravitational instability models with a scale-free approximately scale-invariant spectra.

Scientific results from COBE

NASA's Cosmic Background Explorer (COBE1) carries three scientific instruments to make precise measurements of the spectrum and anisotropy of the cosmic microwave background (CMB) radiation on angular scales greater than 7° and to conduct a search for a diffuse cosmic infrared background (CIB) radiation with 0.7° angular resolution. Data from the Far-InfraRed Absolute Spectrophotometer (FIRAS) show that the spectrum of the CMB is that of a blackbody of temperature T=2.73±0.06 K, with no deviation from a blackbody spectrum greater than 0.25% of the peak brightness. The first year of data from the Differential Microwave Radiometers (DMR) show statistically significant CMB anisotropy. The anisotropy is consistent with a scale invariant primordial density fluctuation spectrum. Infrared sky brightness measurements from the Diffuse InfraRed Background Experiment (DIRBE) provide new conservative upper limits to the CIB. Extensive modeling of solar system and galactic infrared foregrounds is required for further improvement in the CIB limits.

Amplitude of primeval fluctuations from cosmological mass density reconstructions

view Abstract Citations (11) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Amplitude of Primeval Fluctuations from Cosmological Mass Density Reconstructions Seljak, Uros ; Bertschinger, Edmund Abstract We use the POTENT reconstruction of the mass density field in the nearby universe to estimate the amplitude of the density fluctuation power spectrum for various cosmological models. We find sigma_8\Omega_m^{0.6}= 1.3^{+0.4}_{-0.3}, almost independently of the power spectrum. This value agrees well with the COBE normalization for the standard CDM model, while some alternative models predict an excessive amplitude compared with COBE. Flat low \Omega_m models and tilted models with spectral index n<0.8 are particularly discordant. Publication: The Astrophysical Journal Pub Date: June 1994 DOI: 10.1086/174163 arXiv: arXiv:astro-ph/9311072 Bibcode: 1994ApJ...427..523S Keywords: Astronomical Models; Background Radiation; Cosmology; Density Distribution; Flux Density; Mass Distribution; Matter (Physics); Microwaves; Power Spectra; Radiation Spectra; Space Density; Cosmic Background Explorer Satellite; Dark Matter; Galactic Rotation; Hubble Constant; Perturbation Theory; Radial Velocity; Universe; Velocity Distribution; Astrophysics; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; Astrophysics E-Print: 10 pages, AAS Latex v3.0, 1 figure and postscript available by anonymous ftp to arcturus.mit.edu, ApJ, in press 1994, preprint MIT-CSR-93-33 full text sources arXiv | ADS |

Tensor perturbations in inflationary models as a probe of cosmology.

In principle, the tensor metric (gravity-wave) perturbations that arise in inflationary models can, beyond probing the underlying inflationary model, provide information about the Universe: ionization history, presence of a cosmological constant, and epoch of matter-radiation equality. Because tensor perturbations give rise to the anisotropy of the cosmic background radiation (CBR) solely through the Sachs-Wolfe effect we are able to calculate analytically their contribution to the variance of the multipole moments of the CBR temperature anisotropy. In so doing, we carefully take account of the effect of tensor perturbations that entered the Hubble radius during both the matter-dominated and radiation-dominated epochs by means of a transfer function. (Previously, only those modes that entered during the matter era were properly taken into account.) The striking feature in the spectrum of multipole amplitudes is a dramatic falloff for l\ensuremath{\gtrsim} \ensuremath{\surd}1+${\mathit{z}}_{\mathrm{LSS}}$ , where ${\mathit{z}}_{\mathrm{LSS}}$ is the redshift of the last-scattering surface, which depends upon the ionization history of the Universe. Finally, using our transfer function we provide a more precise formula for the energy density in stochastic gravitational waves from inflation, and, using the Cosmic Background Explorer Differential Microwave Radiometer (COBE DMR) quadrupole normalization, we express this energy density in terms of the ``tilt'' of the spectrum of tensor perturbations alone and show that it is unlikely that the stochastic background of gravity waves can be detected directly in the foreseeable future.