Lloyd Knox

University of California, Davis

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Yong‐Seon Song

Korea Astronomy and Space Science Institute

Andreas Albrecht

University of California, Davis

M. Millea

University of California, Davis

Francis-Yan Cyr-Racine

University of New Mexico

S. S. Meyer

Fermi National Accelerator Laboratory

D. A. Cottingham

Goddard Space Flight Center

Zhen Pan

Hefei National Center for Physical Sciences at Nanoscale

Salman Habib

Karachi Institute of Radiotherapy and Nuclear Medicine

Katrin Heitmann

Argonne National Laboratory

Asantha Cooray

University of California, Irvine

Cooperative Institutions

University of Chicago

University of California, Berkeley

Fermi National Accelerator Laboratory

Kavli Institute for Particle Astrophysics and Cosmology

Lawrence Berkeley National Laboratory

University of California, Davis

Princeton University

California Institute of Technology

Jet Propulsion Laboratory

McGill University

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Determining Neutrino Mass from the Cosmic Microwave Background Alone

Physical Review Letters (2003)

Manoj Kaplinghat Lloyd Knox Yong‐Seon Song

Distortions of Cosmic Microwave Background (CMB) temperature and polarization maps caused by gravitational lensing, observable with high angular resolution and high sensitivity, can be used to measure the neutrino mass. Assuming two massless species and one with mass m_nu we forecast sigma(m_nu) = 0.15 eV from the Planck satellite and sigma(m_nu)=0.04 eV from observations with twice the angular resolution and about 20 times the sensitivity. A detection is likely at this higher sensitivity since the observation of atmospheric neutrino oscillations require mass-squared differences greater than about (0.04 eV)^2.

Massless particle

Cosmic background radiation

Sigma

Cosmic neutrino background

10.1103/physrevlett.91.241301

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Citations (201)

First Detection of the Acoustic Oscillation Phase Shift Expected from the Cosmic Neutrino Background

Physical Review Letters (2015)

Brent Follin Lloyd Knox M. Millea Zhen Pan

The unimpeded relativistic propagation of cosmological neutrinos prior to recombination of the baryon-photon plasma alters gravitational potentials and therefore the details of the time-dependent gravitational driving of acoustic oscillations. We report here a first detection of the resulting shifts in the temporal phase of the oscillations, which we infer from their signature in the cosmic microwave background temperature power spectrum.

Baryon Acoustic Oscillations

Cosmic neutrino background

Oscillation (cell signaling)

10.1103/physrevlett.115.091301

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Citations (144)

Detectability of Tensor Perturbations through Anisotropy of The Cosmic Background Radiation

Physical Review Letters (1994)

Lloyd Knox Michael S. Turner

Detection of the tensor perturbations predicted in inflationary models is important for testing inflation as well as for reconstructing the inflationary potential. We show that because of cosmic variance the tensor contribution to the square of the cosmic background radiation quadrupole anisotropy must be greater than about 14% of the scalar contribution to ensure a statistically significant detection of tensor perturbations. This sensitivity could be achieved by full-sky measurements on angular scales of 3\ifmmode^\circ\else\textdegree\fi{} and 0.5\ifmmode^\circ\else\textdegree\fi{}.

Cosmic background radiation

Background radiation

Cosmic string

Massless particle

10.1103/physrevlett.73.3347

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Citations (58)

Reionization of the Intergalactic Medium and its Effect on the CMB

Zoltán Haiman Lloyd Knox

The bulk of the hydrogen in the universe transformed from neutral to ionized somewhere in the redshift interval 5 < z < 40, most likely due to ionizing photons produced by an early generation of stars or mini-quasars. The resulting free electrons, interacting with the CMB photons via Thomson scattering, are a mixed blessing, providing both a probe of the epoch of the first stars and a contaminant to the pristine primary anisotropy. Here we review our current knowledge of reionization with emphasis on inhomogeneities and describe the possible connections to CMB anisotropy.

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Measuring Cross-Spectra of the Cosmic Infrared Background from 95 to 1200 GHz

arXiv (Cornell University) (2018)

M. Viero C. L. Reichardt B. A. Benson L. E. Bleem J. J. Bock

We present measurements of the power spectra of cosmic infrared background (CIB) and cosmic microwave background (CMB) fluctuations in six frequency bands. Maps at the lower three frequency bands, 95, 150, and 220 GHz (3330, 2000, 1360 $\mu$m) are from the South Pole Telescope, while the upper three frequency bands, 600, 857, and 1200 GHz (500, 350, 250 $\mu$m) are observed with Herschel/SPIRE. From these data, we produce 21 angular power spectra (six auto- and fifteen cross-frequency) spanning the multipole range $600 \le \ell \le 11,000$. Our measurements are the first to cross-correlate measurements near the peak of the CIB spectrum with maps at 95 GHz, complementing and extending the measurements from Planck Collaboration et al. (2014) at 218, 550, and 857 GHz. The observed fluctuations originate largely from clustered, infrared- emitting, dusty star-forming galaxies, the CMB, and to a lesser extent radio galaxies, active galactic nuclei, and the Sunyaev-Zel'dovich effect.

Cosmic infrared background

South Pole Telescope

Spire (mollusc)

Radio spectrum

Cosmic background radiation

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Tuning Goodness-of-Fit Tests

arXiv (Cornell University) (2017)

Andrew Arrasmith Brent Follin Ethan Anderes Lloyd Knox

As modern precision cosmological measurements continue to show agreement with the broad features of the standard $\Lambda$-Cold Dark Matter ($\Lambda$CDM) cosmological model, we are increasingly motivated to look for small departures from the standard model's predictions which might not be detected with standard approaches. While searches for extensions and modifications of $\Lambda$CDM have to date turned up no convincing evidence of beyond-the-standard-model cosmology, the list of models compared against $\Lambda$CDM is by no means complete and is often governed by readily-coded modifications to standard Boltzmann codes. Also, standard goodness-of-fit methods such as a naive $\chi^2$ test fail to put strong pressure on the null $\Lambda$CDM hypothesis, since modern datasets have orders of magnitudes more degrees of freedom than $\Lambda$CDM. Here we present a method of tuning goodness-of-fit tests to detect potential sub-dominant extra-$\Lambda$CDM signals present in the data through compressing observations in a way that maximizes extra-$\Lambda$CDM signal variation over noise and $\Lambda$CDM variation. This method, based on a Karhunen-Lo\`{e}ve transformation of the data, is tuned to be maximally sensitive to particular types of variations characteristic of the tuning model; but, unlike direct model comparison, the test is also sensitive to features that only partially mimic the tuning model. As an example of its use, we apply this method in the context of a nonstandard primordial power spectrum compared against the $2015$ $Planck$ CMB temperature and polarization power spectrum. We find weak evidence of extra-$\Lambda$CDM physics, conceivably due to known systematics in the 2015 Planck polarization release.

Goodness of fit

Matter power spectrum

10.48550/arxiv.1705.03565

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The Case for Deep, Wide-Field Cosmology

arXiv (Cornell University) (2009)

Ryan Scranton Andreas Albrecht R. R. Caldwell Asantha Cooray Olivier Doré

Much of the science case for the next generation of deep, wide-field optical/infrared surveys has been driven by the further study of dark energy. This is a laudable goal (and the subject of a companion white paper by Zhan et al.). However, one of the most important lessons of the current generation of surveys is that the interesting science questions at the end of the survey are quite different than they were when the surveys were being planned. The current surveys succeeded in this evolving terrain by being very general tools that could be applied to a number of very fundamental measurements. Likewise, the accessibility of the data enabled the broader cosmological and astronomical community to generate more science than the survey collaborations could alone. With that in mind, we should consider some of the basic physical and cosmological questions that surveys like LSST and JDEM-Wide will be able to address.

White paper

10.48550/arxiv.0902.2590

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Cosmic microwave background acoustic peak locations

Monthly Notices of the Royal Astronomical Society (2016)

Zhen Pan Lloyd Knox Brigid Mulroe Ali Narimani

The Planck collaboration has measured the temperature and polarization of the cosmic microwave background well enough to determine the locations of eight peaks in the temperature (TT) power spectrum, five peaks in the polarization (EE) power spectrum and twelve extrema in the cross (TE) power spectrum. The relative locations of these extrema give a striking, and beautiful, demonstration of what we expect from acoustic oscillations in the plasma; e.g., that EE peaks fall half way between TT peaks. We expect this because the temperature map is predominantly sourced by temperature variations in the last scattering surface, while the polarization map is predominantly sourced by gradients in the velocity field, and the harmonic oscillations have temperature and velocity 90 degrees out of phase. However, there are large differences in expectations for extrema locations from simple analytic models vs. numerical calculations. Here we quantitatively explore the origin of these differences in gravitational potential transients, neutrino free-streaming, the breakdown of tight coupling, the shape of the primordial power spectrum, details of the geometric projection from three to two dimensions, and the thickness of the last scattering surface. We also compare the peak locations determined from Planck measurements to expectations under the $\Lambda$CDM model. Taking into account how the peak locations were determined, we find them to be in agreement.

Baryon Acoustic Oscillations

Maxima and minima

Matter power spectrum

Cosmic background radiation

10.1093/mnras/stw833

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Citations (25)

Weak Lensing and Supernovae: Complementary Probes of Dark Energy

arXiv (Cornell University) (2004)

Lloyd Knox Andreas Albrecht Yong‐Seon Song

Weak lensing observations and supernova observations, combined with CMB observations, can both provide powerful constraints on dark energy properties. Considering statistical errors only, we find luminosity distances inferred from 2000 supernovae and large-scale (l < 1000) angular power spectra inferred from redshift-binned cosmic shear maps place complementary constraints on w_0 and w_a where w(z) = w_0 + w_a(a-1). Further, each set of observations can constrain higher-dimensional parameterizations of w(z); we consider eigenmodes of the w(z) error covariance matrix and find such datasets can each constrain the amplitude of about 5 w(z) eigenmodes. We also consider another parameterization of the dark energy.

10.48550/arxiv.astro-ph/0408141

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Citations (3)

Primordial nucleosynthesis in conformal Weyl gravity

Lloyd Knox Arthur Kosowsky

Recently conformal Weyl gravity has been considered as a candidate alternative gravity theory. This fourth-order theory is attractive because it is the only metric theory of gravity which is invariant under local conformal transformations of the metric. The authors calculate the primordial light element abundances in this theory. The major difference from the standard cosmology is that the universe expands far more slowly throughout the nucleosynthesis epoch. The production of {sup 4}He depends strongly on {eta}, the ratio of baryons to photons. For {eta} = 10{sup {minus}8} the mass fraction of {sup 4}He is X{sub 4} {approx_equal} 0.25 and the number densities relative to hydrogen for {sup 2}H, {sup 3}He and {sup 7}Li are n({sup 2}H)/n(H) {approx_equal} 9 {times} 10{sup {minus}20}, n({sup 3}He)/n(H) {approx_equal}4 {times} 10{sup {minus}18} and n({sup 7}Li)/n(H) {approx_equal} 10{sup {minus}13}. This value of {eta} corresponds to a baryon mass density close to the standard model critical density. However, adjusting {eta} to give a reasonable helium yield forces the deuterium and lithium yields to be small enough that the theory cannot be reconciled with observations.

Big Bang nucleosynthesis

Conformal gravity

Isotopes of helium

10.2172/10194676

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Citations (6)