arXiv subjects

Raphael Flauger

Publications and source records attributed to Raphael Flauger.

At least 55 records · Page 3Linked to original sources

arXiv2017

Robustness of Inflation to Inhomogeneous Initial Conditions

We consider the effects of inhomogeneous initial conditions in both the scalar field profile and the extrinsic curvature on different inflationary models. In particular, we compare the robustness of small field inflation to that of large field inflation, using numerical simulations with Einstein gravity in 3+1 dimensions. We find that small field inflation can fail in the presence of subdominant gradient energies, suggesting that it is much less robust to inhomogeneities than large field inflation, which withstands dominant gradient energies. However, we also show that small field inflation can be successful even if some regions of spacetime start out in the region of the potential that does not support inflation. In the large field case, we confirm previous results that inflation is robust if the inflaton occupies the inflationary part of the potential. Furthermore, we show that increasing initial scalar gradients will not form sufficiently massive inflation-ending black holes if the initial hypersurface is approximately flat. Finally, we consider the large field case with a varying extrinsic curvature K, such that some regions are initially collapsing. We find that this may again lead to local black holes, but overall the spacetime remains inflationary if the spacetime is open, which confirms previous theoretical studies.

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arXiv2017

CMB constraints on primordial black hole dark matter

We revisit cosmic microwave background (CMB) constraints on primordial black hole dark matter. Spectral distortion limits from COBE/FIRAS do not impose a relevant constraint. Planck CMB anisotropy power spectra imply that primordial black holes with $m_{BH}\gtrsim 5~M_{\odot}$ are disfavored. However, this is susceptible to sizeable uncertainties due to the treatment of the black hole accretion process. These constraints are weaker than those quoted in earlier literature for the same observables.

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arXiv2016

CMB-S4 Science Book, First Edition

This book lays out the scientific goals to be addressed by the next-generation ground-based cosmic microwave background experiment, CMB-S4, envisioned to consist of dedicated telescopes at the South Pole, the high Chilean Atacama plateau and possibly a northern hemisphere site, all equipped with new superconducting cameras. CMB-S4 will dramatically advance cosmological studies by crossing critical thresholds in the search for the B-mode polarization signature of primordial gravitational waves, in the determination of the number and masses of the neutrinos, in the search for evidence of new light relics, in constraining the nature of dark energy, and in testing general relativity on large scales.

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arXiv2016

Productive Interactions: heavy particles and non-Gaussianity

We analyze the shape and amplitude of oscillatory features in the primordial power spectrum and non-Gaussianity induced by periodic production of heavy degrees of freedom coupled to the inflaton $ϕ$. We find that non-adiabatic production of particles can contribute effects which are detectable or constrainable using cosmological data even if their time-dependent masses are always heavier than the scale $\dot ϕ^{1/2}$, much larger than the Hubble scale. This provides a new role for UV completion, consistent with the criteria from effective field theory for when heavy fields cannot be integrated out. This analysis is motivated in part by the structure of axion monodromy, and leads to an additional oscillatory signature in a subset of its parameter space. At the level of a quantum field theory model that we analyze in detail, the effect arises consistently with radiative stability for an interesting window of couplings up to of order $\lesssim 1$. The amplitude of the bispectrum and higher-point functions can be larger than that for Resonant Non-Gaussianity, and its signal/noise may be comparable to that of the corresponding oscillations in the power spectrum (and even somewhat larger within a controlled regime of parameters). Its shape is distinct from previously analyzed templates, but was partly motivated by the oscillatory equilateral searches performed recently by the {\it Planck} collaboration. We also make some general comments about the challenges involved in making a systematic study of primordial non-Gaussianity.

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arXiv2015

Planck Data Reconsidered

The tension between the best fit parameters derived by the Planck team and a number of other astronomical measurements suggests either systematics in the astronomical measurements, systematics in the Planck data, the need for new physics, or a combination thereof. We re-analyze the Planck data and find that the $217\,\text{GHz}\times 217\,\text{GHz}$ detector set spectrum used in the Planck analysis is responsible for some of this tension. We use a map-based foreground cleaning procedure, relying on a combination of 353 GHz and 545 GHz maps to reduce residual foregrounds in the intermediate frequency maps used for cosmological inference. For our baseline data analysis, which uses 47% of the sky and makes use of both 353 and 545 GHz data for foreground cleaning, we find the $Λ$CDM cosmological parameters $Ω_c h^2 = 0.1170 \pm 0.0025$, $n_s = 0.9686 \pm 0.0069$, $H_0 = 68.0 \pm 1.1\,\mathrm{km} \mathrm{s}^{-1}\mathrm{Mpc}^{-1}$, $Ω_b h^2 = 0.02197 \pm 0.00026$, $\ln 10^{10}A_s = 3.082 \pm 0.025$, and $τ= 0.090 \pm 0.013 $. While in broad agreement with the results reported by the Planck team, these revised parameters imply a universe with a lower matter density of $Ω_m=0.302\pm0.015$, and parameter values generally more consistent with pre-Planck CMB analyses and astronomical observations. We compare our cleaning procedure with the foreground modeling used by the Planck team and find good agreement. The difference in parameters between our analysis and that of the Planck team is mostly due to our use of cross-spectra from the publicly available survey maps instead of their use of the detector set cross-spectra which include pixels only observed in one of the surveys. We show evidence suggesting residual systematics in the detector set spectra used in the Planck likelihood code, which is substantially reduced for our spectra.

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arXiv2015

Flux Tube Spectra from Approximate Integrability at Low Energies

We provide a detailed introduction to a method we recently proposed for calculating the spectrum of excitations of effective strings such as QCD flux tubes. The method relies on the approximate integrability of the low energy effective theory describing the flux tube excitations and is is based on the Thermodynamic Bethe Ansatz (TBA). The approximate integrability is a consequence of the Lorentz symmetry of QCD. For excited states the convergence of the TBA technique is significantly better than that of the traditional perturbative approach. We apply the new technique to the lattice spectra for fundamental flux tubes in gluodynamics in D=3+1 and D=2+1, and to k-strings in gluodynamics in D=2+1. We identify a massive pseudoscalar resonance on the world sheet of the confining strings in SU(3) gluodynamics in D=3+1, and massive scalar resonances on the world sheet of k=2,3 strings in SU(6) gluodynamics in D=2+1.

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arXiv2014

Drifting Oscillations in Axion Monodromy

We study the pattern of oscillations in the primordial power spectrum in axion monodromy inflation, accounting for drifts in the oscillation period that can be important for comparing to cosmological data. In these models the potential energy has a monomial form over a super-Planckian field range, with superimposed modulations whose size is model-dependent. The amplitude and frequency of the modulations are set by the expectation values of moduli fields. We show that during the course of inflation, the diminishing energy density can induce slow adjustments of the moduli, changing the modulations. We provide templates capturing the effects of drifting moduli, as well as drifts arising in effective field theory models based on softly broken discrete shift symmetries, and we estimate the precision required to detect a drifting period. A non-drifting template suffices over a wide range of parameters, but for the highest frequencies of interest, or for sufficiently strong drift, it is necessary to include parameters characterizing the change in frequency over the e-folds visible in the CMB. We use these templates to perform a preliminary search for drifting oscillations in a part of the parameter space in the Planck nominal mission data.

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arXiv2014

Toward an Understanding of Foreground Emission in the BICEP2 Region

BICEP2 has reported the detection of a degree-scale B-mode polarization pattern in the Cosmic Microwave Background (CMB) and has interpreted the measurement as evidence for primordial gravitational waves. Motivated by the profound importance of the discovery of gravitational waves from the early Universe, we examine to what extent a combination of Galactic foregrounds and lensed E-modes could be responsible for the signal. We reanalyze the BICEP2 results and show that the 100x150 GHz and 150x150 GHz data are consistent with a cosmology with r=0.2 and negligible foregrounds, but also with a cosmology with r=0 and a significant dust polarization signal. We give independent estimates of the dust polarization signal in the BICEP2 region using four different approaches. While these approaches are consistent with each other, the expected amplitude of the dust polarization power spectrum remains uncertain by about a factor of three. The lower end of the prediction leaves room for a primordial contribution, but at the higher end the dust in combination with the standard CMB lensing signal could account for the BICEP2 observations, without requiring the existence of primordial gravitational waves. By measuring the cross-correlations between the pre-Planck templates used in the BICEP2 analysis and between different versions of a data-based template, we emphasize that cross-correlations between models are very sensitive to noise in the polarization angles and that measured cross-correlations are likely underestimates of the contribution of foregrounds to the map. These results suggest that BICEP1 and BICEP2 data alone cannot distinguish between foregrounds and a primordial gravitational wave signal, and that future Keck Array observations at 100 GHz and Planck observations at higher frequencies will be crucial to determine whether the signal is of primordial origin. (abridged)

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arXiv2013

Evidence for a new particle on the worldsheet of the QCD flux tube

We propose a new approach for the calculation of the spectrum of excitations of QCD flux tubes. It relies on the fact that the worldsheet theory is integrable at low energies. With this approach, energy levels can be calculated for much shorter flux tubes than was previously possible, allowing for a quantitative comparison with existing lattice data. The improved theoretical control makes it manifest that existing lattice data provides strong evidence for a new pseudoscalar particle localized on the QCD fluxtube - the worldsheet axion.

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arXiv2013

Planck Constraints on Monodromy Inflation

We use data from the nominal Planck mission to constrain modulations in the primordial power spectrum associated with monodromy inflation. The largest improvement in fit relative to the unmodulated model has Δχ^2~10 and we find no evidence for a primordial signal, in contrast to a previous analysis of the WMAP9 dataset, for which Δχ^2~20. The Planck and WMAP9 results are broadly consistent on angular scales where they are expected to agree as far as best-fit values are concerned. However, even on these scales the significance of the signal is reduced in Planck relative to WMAP, and is consistent with a fit to the noise associated with cosmic variance. Our results motivate both a detailed comparison between the two experiments and a more careful study of the theoretical predictions of monodromy inflation.

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arXiv2013

Constraining Monodromy Inflation

We use cosmic microwave background (CMB) data from the 9-year WMAP release to derive constraints on monodromy inflation, which is characterized by a linear inflaton potential with a periodic modulation. We identify two possible periodic modulations that significantly improve the fit, but it is unclear whether this improvement is associated with a "signal" or with the scatter in the measured angular power spectrum. The unmodulated potential is mildly favored by standard model selection criteria. A modulated inflationary potential can generate substantial primordial non-Gaussianity, of a specific and characteristic form. For the best-fit parameters to the WMAP angular power spectrum, the corresponding non-Gaussianity might be detectable in upcoming CMB data, allowing nontrivial consistency checks on the predictions of a modulated inflationary potential.

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arXiv2013

On Squeezed Limits in Single-Field Inflation - Part I

The n-point correlation functions in single-field inflation obey a set of consistency conditions in the exact squeezed limit which are not present in multi-field models, and thus are powerful tools to distinguish between the two. However, these consistency conditions may be violated for a finite range of scales in single-field models, for example by departures from the Bunch-Davies state. These it excited states may be the consequence of interactions during inflation, or may be a remnant of the era that preceded inflation. In this paper we analyze the bispectrum, and show that in the regime of theoretical control the resulting signal in the squeezed limit remains undetectably small in all known models which continuously excite the state. We also show that the signal remains undetectably small if the initial state is related to the Bunch-Davies state by a Bogoliubov transformation and the energy density in the state is small enough so that the usual slow-roll conditions are obeyed. Bogoliubov states that lead to violations of the slow-roll conditions, as well as more general excited states, require more careful treatment and will be discussed in a separate publication.

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arXiv2013

Effective String Theory Revisited

We revisit the effective field theory of long relativistic strings such as confining flux tubes in QCD. We derive the Polchinski-Strominger interaction by a calculation in static gauge. This interaction implies that a non-critical string which initially oscillates in one direction gets excited in orthogonal directions as well. In static gauge no additional term in the effective action is needed to obtain this effect. It results from a one-loop calculation using the Nambu-Goto action. Non-linearly realized Lorentz symmetry is manifest at all stages in dimensional regularization. We also explain that independent of the number of dimensions non-covariant counterterms have to be added to the action in the commonly used zeta-function regularization.

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arXiv2013

Solving the Simplest Theory of Quantum Gravity

We solve what is quite likely the simplest model of quantum gravity, the worldsheet theory of an infinitely long, free bosonic string in Minkowski space. Contrary to naive expectations, this theory is non-trivial. We illustrate this by constructing its exact factorizable S-matrix. Despite its simplicity, the theory exhibits many of the salient features expected from more mature quantum gravity models, including the absence of local off-shell observables, a minimal length, a maximum achievable (Hagedorn) temperature, as well as (integrable relatives of) black holes. All these properties follow from the exact S-matrix. We show that the complete finite volume spectrum can be reconstructed analytically from this S-matrix with the help of the thermodynamic Bethe Ansatz. We argue that considered as a UV complete relativistic two-dimensional quantum field theory the model exhibits a new type of renormalization group flow behavior, "asymptotic fragility". Asymptotically fragile flows do not originate from a UV fixed point.

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arXiv2012

The One-Loop Effective Kähler Potential. I: Chiral Multiplets

We derive a universal formula for the one-loop renormalization of the effective Kähler potential that applies to general supersymmetric effective field theories of chiral multiplets, with arbitrary interactions respecting N=1 supersymmetry in four dimensions. The resulting expression depends only on the tree-level mass spectrum and the form of the regulator. This formula simplifies and generalizes existing results in the literature. We include two examples to illustrate its use.

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arXiv2011

Oscillons After Inflation

Oscillons are massive, long-lived, localized excitations of a scalar field. We show that in a large class of well-motivated single-field models, inflation is followed by self-resonance, leading to copious oscillon generation and a lengthy period of oscillon domination. These models are characterized by an inflaton potential which has a quadratic minimum and is shallower than quadratic away from the minimum. This set includes both string monodromy models and a class of supergravity inspired scenarios, and is in good agreement with the current central values of the concordance cosmology parameters. We assume that the inflaton is weakly coupled to other fields, so as not to quickly drain energy from the oscillons or prevent them from forming. An oscillon-dominated universe has a greatly enhanced primordial power spectrum on very small scales relative to that seen with a quadratic potential, possibly leading to novel gravitational effects in the early universe.

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arXiv2011

Constraining holographic inflation with WMAP

In a class of recently proposed models, the early universe is strongly coupled and described holographically by a three-dimensional, weakly coupled, super-renormalizable quantum field theory. This scenario leads to a power spectrum of scalar perturbations that differs from the usual empirical LCDM form and the predictions of generic models of single field, slow roll inflation. This spectrum is characterized by two parameters: an amplitude, and a parameter g related to the coupling constant of the dual theory. We estimate these parameters, using WMAP and other astrophysical data. We compute Bayesian evidence for both the holographic model and standard LCDM and find that their difference is not significant, although LCDM provides a somewhat better fit to the data. However, it appears that Planck will permit a definitive test of this holographic scenario.

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arXiv2010

Delayed Reheating and the Breakdown of Coherent Oscillations

We analyze the evolution of the perturbations in the inflaton field and metric following the end of inflation. We present accurate analytic approximations for the perturbations, showing that the coherent oscillations of the post-inflationary condensate necessarily break down long before any current phenomenological constraints require the universe to become radiation dominated. Further, the breakdown occurs on length-scales equivalent to the comoving post-inflationary horizon size. This work has implications for both the inflationary "matching" problem, and the possible generation of a stochastic gravitational wave background in the post-inflationary universe.

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