LES PUBLICATIONS

Reionization in the dark and the light from Cosmic Microwave Background

Date of publication: 

2018-07-14 14:00:00

Author: 

Dhiraj Kumar Hazra, Daniela Paoletti, Fabio Finelli, George F. Smoot

We explore the constraints on the history of reionization from Planck 2015 Cosmic Microwave Background (CMB) data and we derive the forecasts for future CMB observations. We consider a class of monotonic histories of reionization as parametrized by two additional extra parameters with respect to the average optical depth used in the instantaneous reionization modeling. We investigate the degeneracies between the history of reionization and selected extensions of the standard cosmological model. In particular, we consider the degeneracies with the total mass of the neutrino sector and we discuss the possible correlation between the dark matter annihilation and the duration of reionization in the CMB. We use an extension to poly-reion model that was proposed in Hazra and Smoot, JCAP 1711, 028 (2017). We compare the constraints from Planck 2015 data with the predicted constraints from possible future CMB mission as LiteBIRD, and we also use the proposed CORE-like specifications as an example of what higher resolution can bring in addition. We find that the degeneracy between the average optical depth and the duration of reionization will be substantially removed by both concepts. Degeneracies between the reionization history and either the total neutrino mass and properties of dark matter annihilation will also be improved by future surveys. We find only marginal improvement in the constraints on reionization history for the higher resolution in the case of long duration of reionization.

A Soliton Solution for the Central Dark Masses in Globular Clusters and Implications for the Axiverse

Date of publication: 

2018-06-12 16:00:00

Author: 

Razieh Emami, Tom Broadhurst, George Smoot, Tzihong Chiueh, Luu Hoang Nhan

Compact dark masses of ≃2000M⊙ have been derived at the centers of well studied globular clusters orbiting our galaxy, representing ≃0.1% of the mass of these compact stellar systems. It is tempting to conclude these dark masses are long sought examples of "intermediate mass" black holes (IMBH), although no confirming radio/X-ray emission is detected and extended sizes of ≃0.09 pc are permitted by the observations that are much larger than the Schwartzchild radius (≃3×10−4 pc). Here we offer a standing wave explanation for the observed properties of these dark objects, corresponding to a soliton of light bosons, m18=(7.705±7.125)eV, that should develop in the deep gravitational potentials of globular clusters orbiting within the dark halo of our galaxy, from the presence a only a small fraction, ≃10−2, of the dark matter in this form. This would add to the dominant Universal dark matter that is increasingly interpreted as a lighter boson of 10−22eV, implied by the large dark cores of dwarf spheroidal galaxies. Identification of two such light bosonic mass scales of 10−18eV and 10−22eV, favors a generic string theory prediction as dimensional compactification generates a wide, discrete mass spectrum of axionic scalar fields. Observations with improved resolution can test this important theory for the dark matter by resolving our predicted soliton scale, below ≃0.1 pc

Characteristics and energy dependence of recurrent galactic cosmic-ray flux depressions and of a Forbush decrease with LISA Pathfinder

Date of publication: 

2018-04-23 16:00:00

Author: 

M. Armano, H. Audley, J. Baird, M. Bassan, S. Benella, P. Binetruy, M. Born, D. Bortoluzzi, A. Cavalleri, A. Cesarini, A. M. Cruise, K. Danzmann, M. de Deus Silva, I. Diepholz, G. Dixon, R. Dolesi, M. Fabi, L. Ferraioli, V. Ferroni, N. Finetti, E. D. Fitzsimons, M. Freschi, L. Gesa, F. Gibert, D. Giardini, R. Giusteri, C. Grimani, J. Grzymisch, I. Harrison, G. Heinzel, M. Hewitson, D. Hollington, D. Hoyland, M. Hueller, H. Inchauspé, O. Jennrich, P. Jetzer, N. Karnesis, B. Kaune, N. Korsakova, C. J. Killow, M. Laurenza, J. A. Lobo, I. Lloro, L. Liu, J. P. López-Zaragoza, R. Maarschalkerweerd, D. Mance, V. Martín, L. Martin-Polo, J. Martino, F. Martin-Porqueras, I. Mateos, P. W. McNamara, J. Mendes, L. Mendes, M. Nofrarias, S. Paczkowski, M. Perreur-Lloyd, A. Petiteau, P. Pivato, et al. (24 additional authors not shown)

Galactic cosmic-ray (GCR) energy spectra observed in the inner heliosphere are modulated by the solar activity, the solar polarity and structures of solar and interplanetary origin. A high counting rate particle detector (PD) aboard LISA Pathfinder (LPF), meant for subsystems diagnostics, was devoted to the measurement of galactic cosmic-ray and solar energetic particle integral fluxes above 70 MeV n−1 up to 6500 counts s−1. PD data were gathered with a sampling time of 15 s. Characteristics and energy-dependence of GCR flux recurrent depressions and of a Forbush decrease dated August 2, 2016 are reported here. The capability of interplanetary missions, carrying PDs for instrument performance purposes, in monitoring the passage of interplanetary coronal mass ejections (ICMEs) is also discussed.

Closed trapping horizons without singularity

Date of publication: 

2018-04-11 14:00:00

Author: 

Pierre Binétruy, Alexis Helou, Frédéric Lamy

We dedicate this article to the memory of Pierre Binétruy, who passed away on April 1, 2017. He was our guide in the journey through the darkest regions of the Universe.

In gravitational collapse leading to black hole formation, trapping horizons typically develop inside the contracting matter. Classically, an ingoing trapping horizon moves towards the centre where it reaches a curvature singularity, while an outgoing horizon moves towards the surface of the star where it becomes an isolated, null horizon. However, strong quantum effects at high curvature close to the centre could modify the classical picture substantially, e.g. by deflecting the ingoing horizon to larger radii, until it eventually reunites with the outgoing horizon. We here analyse some existing models of regular "black holes" of finite lifespan formed out of ingoing null shells collapsing from , after giving general conditions for the existence of (singularity-free) closed trapping horizons. We study the energy-momentum tensor of such models by solving Einstein's equations in reverse and give an explicit form of the metric to model a Hawking radiation reaching +. A major flaw of the models aiming at describing the formation of black holes (with a Vaidya limit on ) as well as their evaporation is finally exhibited: they necessarily violate the null energy condition up to , i.e. in a non-compact region of spacetime.

Reinterpreting Low Frequency LIGO/Virgo Events as Magnified Stellar-Mass Black Holes at Cosmological Distances

Date of publication: 

2018-04-05 15:00:00

Author: 

Tom Broadhurst, Jose M. Diego, George Smoot III

Gravitational waves can be focussed by the gravity of an intervening galaxy, just like light, thereby magnifying binary merging events in the far Universe. High magnification by galaxies is found to be responsible for the brightest sources detected in sky surveys, but the low angular resolution of LIGO/Virgo is insufficient to check this lensing possibility directly. Here we find that the first six binary black hole (BBH) merging events reported by LIGO/Virgo show clear evidence for lensing in the plane of observed mass and source distance. The four lowest frequency events follow an apparent locus in this plane, which we can reproduce by galaxy lensing, where the higher the magnification, the generally more distant the source so the wave train is stretched more by the Universal expansion, by factors of 2-4. This revises the reported BBH distances upwards by an order of magnitude, equal to the square root of the magnification. Furthermore, the reported black hole masses must be decreased by 2-4 to counter the larger stretch factor, since the orbital frequency is used to derive the black hole masses. This lowers the masses to 5-15 solar masses, well below the puzzlingly high values of 20-35 solar masses otherwise estimated, with the attraction of finding agreement in mass with black holes orbiting stars in our own Galaxy, thereby implying a stellar origin for the low frequency events in the far Universe. We also show that the other two BBH events of higher frequency detected by LIGO/VIRGO, lie well below the lensing locus, consistent with being nearby and unlensed. If this apparent division between local and distant lensed events is reinforced by new detections then the spins and masses of stellar black holes can be compared over a timespan of 10 billion years by LIGO/Virgo.

Measuring the Galactic Cosmic Ray Flux with the LISA Pathfinder Radiation Monitor

Date of publication: 

2018-01-12 15:00:00

Author: 

M Armano, H Audley, J Baird, P Binetruy, M Born, D Bortoluzzi, E Castelli, A Cavalleri, A Cesarini, M Cruise, K Danzmann, M de Deus Silva, I Diepholz, G Dixon, R Dolesi, L Ferraioli, V Ferroni, N Finetti, E D Fitzsimons, M Freschi, L Gesa, F Gibert, D Giardini, R Giusteri, C Grimani, J Grzymisch, I Harrison, G Heinzel, M Hewitson, D Hollington, D Hoyland, M Hueller, H Inchauspe, O Jennrich, P Jetzer, N Karnesis, B Kaune, N Korsakova, C J Killow, J A Lobo, I Lloro, L Liu, J P Lopez-Zaragoza, R Maarschalkerweerd, D Mance, N Meshskar, V Martin, L Martin-Polo, J Martino, F Martin-Porqueras, I Mateos, P W McNamara, J Mendes, L Mendes, M Nofrarias, S Paczkowski, M Perreur-Lloyd, A Petiteau, P Pivato, E Plagnol, J Ramos-Castro, J Reiche, D I Robertson, F Rivas, G Russano, J Slutsky, C F Sopuerta, et al. (12 additional authors not shown)

Test mass charging caused by cosmic rays will be a significant source of acceleration noise for space-based gravitational wave detectors like LISA. Operating between December 2015 and July 2017, the technology demonstration mission LISA Pathfinder included a bespoke monitor to help characterise the relationship between test mass charging and the local radiation environment. The radiation monitor made in situ measurements of the cosmic ray flux while also providing information about its energy spectrum. We describe the monitor and present measurements which show a gradual 40% increase in count rate coinciding with the declining phase of the solar cycle. Modulations of up to 10% were also observed with periods of 13 and 26 days that are associated with co-rotating interaction regions and heliospheric current sheet crossings. These variations in the flux above the monitor detection threshold (approximately 70 MeV) are shown to be coherent with measurements made by the IREM monitor on-board the Earth orbiting INTEGRAL spacecraft. Finally we use the measured deposited energy spectra, in combination with a GEANT4 model, to estimate the galactic cosmic ray differential energy spectrum over the course of the mission.

Evidence of Neutrino Enhanced Clustering in a Complete Sample of Sloan Survey Clusters, Implying ∑mν=0.11±0.03eV

Date of publication: 

2017-11-18 15:00:00

Author: 

Razieh Emami, Tom Broadhurst, Pablo Jimeno, George Smoot, Raul Angulo, Jeremy Lim, Ming Chung Chu, Ruth Lazkoz

The clustering amplitude of 7143 clusters from the Sloan Digital Sky Survey (SDSS) is found to increase linearly with cluster mass, closely agreeing with the Gaussian random field hypothesis for structure formation. In detail, the observed correlation length exceeds pure cold dark matter (CDM) simulation predictions by ≃6%, for the standard Planck-based values of the cosmological parameters. We show this excess is naturally accounted for by free streaming of light neutrinos, which opposes gravitational growth, so that clusters formed at fixed mass are fewer and hence more biased than for a pure CDM density field. An enhancement in the cluster bias by 7% matches the observations, corresponding to a total neutrino mass, ∑mν=(0.11±0.03)eV, for the standard relic neutrino density. If ongoing laboratory experiments favor a normal neutrino mass hierarchy, then we may infer a somewhat larger total mass than the minimum oscillation based value, ∑mν≃0.056eV, with 95% confidence. Much higher precision can be achieved by applying our method to the more numerous galaxy groups present in the SDSS, for which we predict an appreciable clustering enhancement by neutrinos.

Probing features in the primordial perturbation spectrum with large-scale structure data

Date of publication: 

2017-10-30 14:00:00

Author: 

Benjamin L'Huillier (KASI), Arman Shafieloo (KASI), Dhiraj Kumar Hazra, George F. Smoot, Alexei A. Starobinsky

The form of the primordial power spectrum (PPS) of cosmological scalar (matter density) perturbations is not yet constrained satisfactorily in spite of the tremendous amount of information from the Cosmic Microwave Background (CMB) data. While a smooth power-law-like form of the PPS is consistent with the CMB data, some PPS with small non-smooth features at large scales can also fit the CMB temperature and polarization data with similar statistical evidence. Future CMB surveys cannot help distinguish all such models due to the cosmic variance at large angular scales. In this paper, we study how well we can differentiate between such featured forms of the PPS not otherwise distinguishable using CMB data. We ran 15 N -body DESI-like simulations of these models to explore this approach. Showing that statistics such as the halo mass function and the two-point correlation function are not able to distinguish these models in a DESI-like survey, we advocate to avoid reducing the dimensionality of the problem from 3 to 2 by demonstrating that the use of a simple three- dimensional count-in-cell density field can be much more effective for the purpose of model distinction.

Observational Constraints on the Primordial Curvature Power Spectrum

Date of publication: 

2017-10-26 14:00:00

Author: 

Razieh Emami and George F. Smoot.

CMB observations provide a precise measurement of the primordial power spectrum on large scales, corresponding to wavenumbers 10−3 Mpc−1 < k < 0.1 Mpc−1, [1-8]. Luminous red galaxies and galaxy clusters probe the matter power spectrum on overlapping scales (0.02 Mpc−1 < k < 0.7 Mpc−1 [9-18]), while the Lyman-alpha forest reaches slightly smaller scales (0.3 Mpc−1<k<3 Mpc−1; [19]). These observations indicate that the primordial power spectrum is nearly scale-invariant with amplitude close to 2×10−9, [5, 20-25]. They also strongly support Inflation and motivate us to obtain constraints reaching to smaller scales on the primordial curvature power spectrum and by implication on Inflation. One could obtain limits to much higher values of k<105 Mpc−1 and with less sensitivity even higher to k<1019−1023 Mpc−1 using limits from CMB spectral distortions(SD)and on ultracompact minihalo objects(UCMHs)and Primordial Black Holes(PBHs). In this paper, we revisit and collect all the known constraints on both PBHs and UCMHs. We show that unless one uses SD, PBHs give us very relaxed bounds on the primordial curvature perturbations. UCMHs are very informative over a reasonable k range(3<k<106 Mpc−1)and lead to significant upper-bounds on the curvature spectrum. We review the conditions under which the tighter constraints on the UCMHs could imply extremely strong bounds on the fraction of Dark Matter that could be PBHs. Failure to satisfy these conditions would lead to over production of the UCMHs, which is inconsistent with the observations. Therefore, we can almost rule out PBH within their overlap scales with the UCMHs. We consider the UCMH bounds from experiments such as γ-rays, Neutrinos, Reionization, pulsar-timing and SD. We show that they lead to comparable results independent of the form of DM.

Probing features in inflaton potential and reionization history with future CMB space observations

Date of publication: 

2017-10-03 14:00:00

Author: 

Dhiraj Kumar Hazra, Daniela Paoletti,Mario Ballardini, Fabio Finelli, Arman Shafieloo, George F. Smoot, Alexei A. Starobinsky.

We consider the prospects of probing features in the primordial power spectrum with future Cosmic Microwave Background (CMB) polarization measurements. In the scope of the inflationary scenario, such features in the spectrum can be produced by local non-smooth pieces in an inflaton potential (smooth and quasi-flat in general) which in turn may originate from fast phase transitions during inflation in other quantum fields interacting with the inflaton. They can fit some outliers in the CMB temperature power spectrum which are unaddressed within the standard inflationary ΛCDM model. We consider Wiggly Whipped Inflation (WWI) as a theoretical framework leading to improvements in the fit to the Planck 2015 temperature and polarization data in comparison with the standard inflationary models, although not at a statistically significant level. We show that some type of features in the potential within the WWI models, leading to oscillations in the primordial power spectrum that extend to intermediate and small scales can be constrained with high confidence (at 3σ or higher confidence level) by an instrument as the Cosmic ORigins Explorer (CORE). In order to investigate the possible confusion between inflationary features and footprints from the reionization era, we consider an extended reionization history with monotonic increase of free electrons with decrease in redshift. We discuss the present constraints on this model of extended reionization and future predictions with CORE. We also project, to what extent, this extended reionization can create confusion in identifying inflationary features in the data.

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