Stephen Green (UChicago): Newtonian and Relativistic Cosmologies

Cosmological N-body simulations are now being performed using Newtonian gravity on scales larger than the Hubble radius. It is well known that a uniformly expanding, homogeneous ball of dust in Newtonian gravity satisfies the same equations as arise in relativistic FLRW cosmology, and it also is known that a correspondence between Newtonian and relativistic dust cosmologies continues to hold in linearized perturbation theory in the marginally bound/spatially flat case. Nevertheless, it is far from obvious that Newtonian gravity can provide a good global description of an inhomogeneous cosmology when there is significant nonlinear dynamical behavior at small scales. We investigate this issue in the light of a perturbative framework that we have recently developed, which allows for such nonlinearity at small scales. We propose a relatively straightforward "dictionary"---which is exact at the linearized level---that maps Newtonian dust cosmologies into general relativistic dust cosmologies, and we use our "ordering scheme" to determine the degree to which the resulting metric and matter distribution solve Einstein's equation. We find that Einstein's equation fails to hold at "order 1" at small scales and at "order epsilon" at large scales. We then find the additional corrections to the metric and matter distribution needed to satisfy Einstein's equation to these orders. While these corrections are of some interest in their own right, our main purpose in calculating them is that their smallness should provide a criterion for the validity of the original dictionary (as well as simplified versions of this dictionary). We expect that, in realistic Newtonian cosmologies, these additional corrections will be very small; if so, this should provide strong justification for the use of Newtonian simulations to describe relativistic cosmologies, even on scales larger than the Hubble radius.

1/16/12 Peyton

Informal discussion. Bring papers you would like to see discussed. Simone Ferraro will give a short talk about his work together with Cora and Kendrick:

Supersonic baryon-CDM velocities and CMB B-mode polarization

http://arxiv.org/abs/1110.2182

General Discussion IAS West Seminar room

General Discussion Peyton Dome room

General Discussion IAS West Seminar room

General Discussion Peyton Dome room

General Discussion IAS West Seminar room

General Discussion Peyton Dome room

Blake Sherwin: CMB Lensing Measurements with ACT and ACTPol

General Discussion IAS West Seminar room

"From massive gravity to multi-metric gravity" - Rachel Rosen

Paper Discussion: Marilena LoVerde (IAS) on "Small-scale Power Spectrum Constraints from the CMB energy spectrum" ( http://arxiv.org/abs/1203.2681 )

Assaf Ben-David (Tel Aviv). 

Title: Odd Parity in the CMB and Stringy Topologies

Abstract: If inflation was relatively short, signatures of pre-inflationary physics could be observed at the largest scales. These scales, for which the cosmic variance is large, indeed show several anomalies, such as isotropy breaking and lack of power. Models that affect these scales do so by either adding a one-point contribution to the primordial perturbation or changing its two-point correlation. An example for the former is the introduction of pre-inflationary relics, and for the latter is a non-trivial topology of the universe. Both can lead to interesting symmetries in the CMB that we can search for in the data. In this talk I will present a few such models, their observational signatures and some searches for them in the data. I will focus on a test for anomalous large scale parity in the CMB, motivated by a model of a pre-inflationary particle. This test finds a direction which exhibits odd parity under reflections through the normal plane, anomalous at least at a 3.6 sigma level. In addition, I will consider some non-classical topologies of the universe, allowed by string theory and describe their observational signatures and the searches for these signatures in the CMB data.

Cancelled! Licia Verde (Barcelona). 

New speaker: Catherine Heymans

Title: Career paths in astronomy:  informal discussion for early stage career researchers with Catherine Heymans

Abstract: It's not what you know but who you know that matters" is a phrase usually reserved for the cut-throat world of business.  During this time of global funding crisis however it seems to apply more and more to the world of academia.   It's not always the smartest person who wins the grant or gains the prestigious fellowship, but those who can sell their science.  Come along to this informal lunch time discussion to chat about your experiences and hear top tips on how to make the most out of your research career.

After lunch Catherine is hoping to book slots with you all to talk about your most exciting research result this year.

Mehrdad Mirbabayi (NYU)

Title: Constraints on Resonant non-Gaussianity

Abstract: The inflationary models with a small oscillating component in the potential are known to have oscillatory features in the power spectrum of scalar fluctuations. The models inevitably produce oscillatory 3-point and higher correlation functions -- the resonant non-Gaussianity. I will argue that unitarity of the effective field theory of inflation ensures that the signal in the 2-point function is dominant over that of the higher correlation functions. Therefore the signatures of oscillations are more likely to be detected in the power spectrum.  

Guido D'Amico (NYU)

Title: Cosmologies in massive gravity.

Abstract: I will review the recently formulated ghost-free Lorentz-invariant massive gravity theory, and I will focus in particular on its cosmological solutions.

In the simplest version of the theory, there are no flat FRW cosmologies, but we can construct solutions which are a good approximation to GR cosmologies.

I will argue that these have problems at the level of perturbations, and illustrate generalizations of the theory which allow for generic, well-behaved cosmological solutions

Jorge Norena (ICC, Barcelona)

Title: Conformal consistency relations for single field inflation.

Abstract: We generalize the single-field consistency relations to

capture not only the leading term in the squeezed limit---going as

1/q^3, where q is the small wavevector---but also the subleading one,

going as 1/q^2. This term, for an (n+1)-point function, is fixed in

terms of the variation of the n-point function under a special

conformal transformation; this parallels the fact that the 1/q^3 term

is related with the scale dependence of the n-point function. For the

squeezed limit of the 3-point function, this conformal consistency

relation implies that there are no terms going as 1/q^2. In models

with reduced speed of sound the conformal consistency conditions

capture, at the level of observables, the relation among operators

induced by the non-linear realization of Lorentz invariance in the

Lagrangian. These results mean that, in any single-field model,

primordial correlation functions of \zeta are endowed with an SO(4,1)

symmetry, with dilations and special conformal transformations

non-linearly realized by \zeta. We briefly comment on some possible

observational consequences of these results.

Based on: arXiv:1203.4595

See also: arXiv:1106.1462, arXiv:1204.6324

Yin-Zhe Ma (UBC)

Testing direction-dependent power spectrum with Planck

 Statistical isotropy is often assumed in cosmology and should be
 tested rigorously against observational data. We construct simple
 quadratic estimators to reconstruct asymmetry in the primordial
 power spectrum from CMB temperature and polarization data and verify
 their accuracy using simulations with quadrupole power asymmetry. We
show that the temperature maps from Planck mission should be able to
constrain the amplitude of any spherical multipole of a scale-invariant
quadrupole asymmetry at the $1\%$ level ($2\sigma$). In addition,
polarization maps are also precise enough to provide complimentary
constraints. Finally,
 we show how to constrain models with axisymmetry in the same
 framework. For scale-free quadrupole models, Planck should constrain
 the direction of the asymmetry to a 1\sigma  accuracy of about 2 degrees
 using one year of temperature data.

Stephen Feeney (University College London)

Laura Book (Caltech)

Title:

Detecting a Gravitational Wave Background with Cosmological Probes

Abstract: It is predicted that a background of gravitational waves was produced in the early universe, and a detection of this background would give us unprecedented insight into the physics at work at early times.  As well as direct detection experiments, which operate at high frequencies, it has been realized that gravitational waves of a wider range of frequencies can be detected indirectly through their effects on cosmological observables, such as the CMB or the positions of astrophysical objects. Both of these are currently being or will in the near future be measured to greater precision than ever before, making these methods of detecting the gravitational wave background very promising. In this talk I will discuss my own recent work on the use of astrometry and CMB lensing to detect or constrain the primordial gravitational wave background.

Fabian Schmidt (Caltech)

Title:Probing the very early Universe with large-scale structure
Abstract: Current and future galaxy surveys will map out a significant portion of the observable Universe.  In addition to telling us about what the Universe is made of and how it evolved, the data can be used to probe the origin of the seed perturbations produced during inflation,
in particular through primordial non-Gaussianity.  I will explain the general idea and give some concrete examples.  I will also discuss some of the theoretical issues that need to be solved in order to realize this potential.

Johannes Noller (Imperial College)

"Non-Gaussianity in single field inflation beyond slow-roll"

In inflationary theories, single field models are typically considered subject to slow-roll conditions. In this talk I will present current observational constraints on deviations from slow-roll, e.g. bounds coming from strong coupling considerations, scale-dependent non-Gaussianities and the tensor-to-scalar ratio. These constraints still allow significant violations of slow-roll conditions. Focusing on non-Gaussian signals, I will discuss a variety of intriguing observable signatures that can be found for fast-rolling single fields.

David J. E. Marsh (Oxford)

Ultra-light Axions: Degeneracies with Massive Neutrinos and Forecasts for Future Cosmological Observations

Subodh Patil (Ecole Normale/Polytechnique Paris)

"Mass hierarchies, decoupling and the imprints of heavy fields during
inflation"

The effective theory (EFT) of inflation is a powerful framework to
consistently parametrize inflationary models at the relevant energy
scales. In an effectively single field setting, all heavy modes that
couple to the inflaton integrate out to a derivative expansion which order
by order is parametrically suppressed by powers of H^2/M^2-- M being the
cutoff of the theory and H being the scale of Inflation. This is what we
mean by heavy fields having decoupled.

In this talk we discuss how certain higher dimensional operators can
become transiently strongly coupled during inflation if the inflaton
trajectory traverses a sharp enough bend in field space. This strong
coupling can compete with the H^2/M^2 suppression enough to result in
corrections to CMB observables that cross the threshold of detectability,
even as slow roll and an effective single field description remain valid.
We argue that these corrections ought to be generic, and are due to the
appearance of a new strong coupling scale during inflation.

Jolyon Bloomfield (Cornell)

"Categorizing Models of Cosmic Acceleration."

Efforts have recently been made to construct an effective field theory for single-field models of dark energy. The same approach as used taken in inflation has been attempted, but dark energy has pitfalls of its own. I will present work on constructing an effective field theory that attempts to describe both the background evolution and perturbations. As part of constructing the theory, techniques for reducing higher order derivative equations of motion and their corresponding actions in a perturbative manner are developed. Close attention is paid to the issue of the choice of conformal frame, and the regime of validity of the effective field theory is investigated in some detail. It is found that seven free functions describe the theory, in contrast to the four found in similar theories of single-field inflation, where matter is not present.

Joseph Smidt (Irvine)

Observational Constraints of Primordial Non-Gaussianity and CMB Lensing.

Measurements of Cosmic Microwave Background (CMB) anisotropies have
served as the strongest experimental probe of the early Universe to
date. If the CMB were a purely Gaussian field, all statistical
information would be contained in the power spectrum or two-point
correlation function. However, non-Gaussianities ensure that new
physics may be extracted from higher n-point correlation functions
including the bispectrum and trispectrum of the CMB.  In this talk I
will discuss new estimators we have formulated to probe primordial
non-Gaussianity in the bispectrum and trispectrum of CMB data and the
constraints we have made using WMAP data while discussing implications
for inflationary models.  I will also discuss how these same methods
may be used to probe other types of physics in higher order
correlation functions such as the amplitude of lensing of the CMB for
which we have also made a constraint using the trispectrum of WMAP
data.

Xiaoying Xu (University of Arizona)

A 2% Measurement of the BAO in SDSS DR7 using Reconstruction

We demonstrate the first application of reconstruction on real
observed galaxies in the SDSS DR7 luminous red galaxy catalogue. We
also introduce more careful approaches to deriving a suitable
covariance matrix and fitting model for galaxy correlation functions.
These all aid in obtaining a more accurate measurement of the acoustic
scale and its error. We validate our reconstruction, covariance matrix
and fitting techniques on 160 mock catalogues derived from the
LasDamas simulations in redshift space. We then apply these techniques
to the DR7 LRG sample and find that the error on the acoustic scale
decreases from ~3.4% before reconstruction to ~1.9% after
reconstruction. This 40% reduction in the error is equivalent to the
effect of increasing the survey volume by about a factor of 3. We also
see an increase by at least 1-sigma in the significance of our BAO
detection for 2 different measures of BAO significance.

Samuel Lee (Johns Hopkins University)

"The phenomenology of light gravitino dark matter"

I will discuss some work on the collider phenomenology and cosmology of

light gravitino dark matter, and will touch on some related issues

concerning infrared divergences in charged-particle decay at finite

temperature.

Light gravitinos, with mass in the eV to MeV range, are well-motivated

in particle physics, but their status as dark-matter candidates is

muddled by early-Universe uncertainties.  Upcoming data from colliders

may clarify this picture.  Light-gravitino collider events should result

in spectacular signals, including di-photons, delayed and non-pointing

photons, kinked charged tracks, and heavy metastable charged particles.

  Remarkably, collider data is also well suited to distinguish between

currently viable light-gravitino cosmological scenarios, with

interesting implications for early-Universe cosmology.  Finally, the

process of charged-particle decay in the early Universe is important in

light-gravitino production, and may also be relevant in other

particle-astrophysics scenarios.  I will examine the cancellation of

power-like infrared divergences that arise at finite temperature, and

will discuss some possible implications for such scenarios.

 Diana Nacir (Universidad de  Buenos Aires, Argentina).

"Dissipative effects in the Effective Field Theory of Inflation"

In this talk I will summarize a recent article arXiv:1109.4192v1 [hep-th] (co-authors: R. Porto, L. Senatore, and M. Zaldarriaga) where we generalized the effective field theory (EFT) of single clock inflation proposed in JHEP 0803:014 (2008) to include dissipative effects.   After some motivations and a brief summary of the EFT of inflation I will describe the  inflationary scenarios we focus on  and how we include the influence of additional degrees of freedom (ADOF) on the dynamics of the perturbations of the clock (which we called $\pi$ field) within the EFT framework. Then,  I will discuss under which circumstances a large friction term of the form $\gamma\dot{\pi}$ leads to an increased level of non-gaussianities.

Tracy Slatyer (DM annihilation and the CMB)

Nissan Itzhaki (Giant Rings in the CMB Sky)

Kendrick Smith (Princeton): Large-scale structure and primordial non-Gaussianity

Adam Brown (Princeton): TBA

+ Daniel Grin (IAS) TBD

canceled so people can attend PCTS meeting on dark matter at Princeton university

Daan Meerburg (Amsterdam): Features in the bispectrum

Sarah Shandera (Perimeter): A generalized local ansatz and its effect on halo bias

Enrico Pajer: Resonant non-Gaussianity and a Dozen More Primordial N-point functions

 Anthony Pullen (Caltech)

1/10/2011 (IAS)

1/17/2011 (Peyton)

informal discussion

Elise Jennings (Durham): TBA

Amitai Bin-Nun: "Gravitational Lensing by Compact Objects in the Galactic Center: The evidence for a boson star" 

2/28/2011 (IAS)

3/7/2011 (Peyton)

3/14/2011 (IAS)

informal discussion

Chris Tully, some ideas on big bang neutrino detection - a potential neutrino capture on tritium experiment at PPPL

5/2/2011

(Peyton)

5/9/2011

(IAS)

Discussion of ways to get around cosmic variance:

Kendrick Smith and Dan Grin http://arxiv.org/abs/1104.3862, 1104.2321, 0807.1770, 0810.0323

5/16/2011

(Peyton)

5/23/2011

(IAS)

5/30/2011

NO MEETING

6/13/2011

(Peyton)

6/20/2011

(IAS)