Research

Summary of key results in last 5 years

My Ph.D. research estimated the effect of non-standard initial state at the onset of inflation on the observed Cosmic Microwave Background (CMB) bispectrum [1, 2]. I developed the enfolded template [3] to search for these effects in the data, which since has become one of the standard templates to look for non-standard initial states in the Universe (both CMB and LSS). The last 5 years my research has focussed on theoretical and data driven studies of the early Universe. I have build techniques to search for primordial features in the CMB power spectrum and bispectrum. In addition, I have performed theoretical studies of the 21-cm signal from the dark ages and reionization, and constrained gravity waves from inflation using a multitude of tracers. I have recently started a ambitious program to build a complete set of estimators to constrain tensor non-Gaussianities, including T, E and B data, with upcoming CMB surveys. I am an active collaborator of the Planck non-Gaussianity and the inflation team. I am one of the coauthors of the CMBS-4 science book inflation chapter, contributing to the non-Gaussianity sections.

Features of new Physics

• In collaboration with Prof. Spergel and Prof. Wandelt I developed a new and highly efficient way to look for features in the CMB power spectrum which has successfully been applied to the Planck data [4, 5, 6, 7].

• Based on initial work on modal expansion [8], in close collaboration with Dr. Münchmyer and Prof. Wandelt, I developed an optimal estimator for resonant CMB bispectra [9] and bispectra from excited states [10]. The techniques developed in these publications has successfully been applied to the data in the latest Planck paper on non-Gaussianity [11].

• I developed statistical tools to estimate significance of feature candidates measured in the CMB power spectrum and the CMB bispectrum [12]. The methods presented in this paper allowed the Planck collaboration to determine the significance of resonant features in the bispectrum [11].

• In close collaboration with Prof. Pajer, I worked out the observational predictions and constraints of gauge field production during inflation, showing that, unlike earlier claims, the CMB power spectrum is more constraining than non-Gaussianities [13].

21-cm

• In collaboration with Dr. Dvorkin and Prof. Spergel I worked out the potential of cross correlating 21-cm fluctuations with fluctuations in the optical depth and showed that this should be less affected to systematics and foregrounds compared to auto-correlations [14].

• In close collaboration with Dr. Ali-Haïmoud, I have worked out all the effects of large scale bulk flows on the 21-cm power spectrum from the dark ages. Most interestingly this could provide a new window into the small scale Universe [15].

• In collaboration with Prof. Chen and Dr. Münchmeyer I forecasted the ultimate limit on features in the power spectrum using the 21 cm power spectrum from the dark ages [16].

Gravity waves

• In collaboration with Dr. Hlozek, Dr. Meyers and a student I demonstrated the power of a multitracer approach in order to constrain the inflationary consistency condition [17].

• I investigated the tentative possibility whether a long wavelength feature from monodromy models of inflation could explain the tension between the BICEP initial results and TT planck data [18].

• In collaboration with Joel Meyers, Alexander van Engelen and Yacine Ali-Haïmoud we showed that the CMB anisotropies can be used to constrain tensor non-Gaussianities. This would provide a consistency check of inflation and is one of the more promising probes of upcoming (ground-based) CMB polarization experiments [19].

References

[1] P. D. Meerburg, J. P. van der Schaar, and M. G. Jackson, “Bispectrum signatures of a modified
vacuum in single field inflation with a small speed of sound,” J. Cosm. Astropart. Phys., vol. 2, p. 1,
Feb. 2010.
[2] P. D. Meerburg and J. P. van der Schaar, “Minimal cutoff vacuum state constraints from CMB bispectrum
statistics,” Phys. Rev. D, vol. 83, p. 043520, Feb. 2011.
[3] P. D. Meerburg, J. P. van der Schaar, and P. S. Corasaniti, “Signatures of initial state modifications
on bispectrum statistics,” J. Cosm. Astropart. Phys., vol. 5, p. 18, May 2009.
[4] P. D. Meerburg, R. A. M. J. Wijers, and J. P. van der Schaar, “WMAP7 constraints on oscillations in
the primordial power spectrum,” Mon. Not. R. Astron. Soc., vol. 421, pp. 369–380, Mar. 2012.
[5] P. D. Meerburg, D. N. Spergel, and B. D. Wandelt, “Searching for oscillations in the primordial power
spectrum. II. Constraints from Planck data,” Phys. Rev. D, vol. 89, p. 063537, Mar. 2014.
[6] P. D. Meerburg, D. N. Spergel, and B. D. Wandelt, “Searching for oscillations in the primordial power
spectrum. I. Perturbative approach,” Phys. Rev. D, vol. 89, p. 063536, Mar. 2014.
[7] P. D. Meerburg, D. N. Spergel, and B. D. Wandelt, “Searching for oscillations in the primordial power
spectrum,” ArXiv e-prints, June 2014.
[8] P. D. Meerburg, “Oscillations in the primordial bispectrum: Mode expansion,” Phys. Rev. D, vol. 82,
p. 063517, Sept. 2010.
[9] M. Münchmeyer, P. D. Meerburg, and B. D. Wandelt, “Optimal estimator for resonance bispectra in
the CMB,” Phys. Rev. D, vol. 91, p. 043534, Feb. 2015.
[10] P. D. Meerburg and M. Münchmeyer, “Optimal CMB estimators for bispectra from excited states,”
ArXiv e-prints, May 2015.
[11] Planck Collaboration, P. A. R. Ade, N. Aghanim, M. Arnaud, F. Arroja, M. Ashdown, J. Aumont,
C. Baccigalupi, M. Ballardini, A. J. Banday, and et al., “Planck 2015 results. XVII. Constraints on
primordial non-Gaussianity,” ArXiv e-prints, Feb. 2015.
[12] P. D. Meerburg, M. Münchmeyer, and B. Wandelt, “Joint resonant CMB power spectrum and bispectrum
estimation,” ArXiv e-prints, Oct. 2015.
[13] P. D. Meerburg and E. Pajer, “Observational constraints on gauge field production in axion inflation,”
J. Cosm. Astropart. Phys., vol. 2, p. 17, Feb. 2013.
[14] P. D. Meerburg, C. Dvorkin, and D. N. Spergel, “Probing Patchy Reionization through -21 cm
Correlation Statistics,” Astrophys. J. , vol. 779, p. 124, Dec. 2013.
[15] Y. Ali-Haïmoud, P. D. Meerburg, and S. Yuan, “New light on 21Â cm intensity fluctuations from the
dark ages,” Phys. Rev. D, vol. 89, p. 083506, Apr. 2014.
[16] X. Chen, P. D. Meerburg, and M. M•nchmeyer, “The Future of Primordial Features with 21 cm
Tomography,” 2016.
[17] P. D. Meerburg, R. Hložek, B. Hadzhiyska, and J. Meyers, “Multiwavelength constraints on the
inflationary consistency relation,” Phys. Rev. D, vol. 91, p. 103505, May 2015.
[18] P. D. Meerburg, “Alleviating the tension at low ℓ through axion monodromy,” Phys. Rev. D, vol. 90,
p. 063529, Sept. 2014.
[19] P. D. Meerburg, J. Meyers, A. van Engelen, and Y. Ali-Ha•moud, “On CMB B-Mode Non-Gaussianity,”
2016.