The 2nd International Conference "Exploring the Energetic Universe 2019"
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Item Open Access Joining bits and pieces of reionization history(NURIS; Energetic Cosmos Laboratory, 2019-04-02) Hazra, Dhiraj Kumar; Paoletti, Daniela; Finelli, Fabio; Smoot, George F.Cosmic Microwave Background temperature and polarization anisotropies from Planck have estimated lower value of the optical depth to reionization (τ) compared to WMAP.Item Open Access Twin LIGO/Virgo Detections of a Viable Gravitationally-Lensed Black Hole Merger(NURIS; Energetic Cosmos Laboratory, 2019-01-10) Broadhurst, Tom; Smoot, George F.; Diego, Jose M.We identify a binary black hole (BBH) merger that appears to be multiply lensed by an intervening galaxy. The LIGO/Virgo events GW170809 and GW170814 have indistinguishable waveforms separated by 5 days, and overlap on the sky within the 90\% credible region. Their strain amplitudes are also similar, implying a modest relative magnification ratio, as expected for a pair of lensed gravitational waves. The phase of the two events is also consistent with being the same, adding more evidence in support of both events originating from the same BBH merger. The difference in the published inferred distances of each event can then be interpreted as following from their different magnifications.Item Open Access Reionization in the dark and the light from Cosmic Microwave Background(NURIS; Energetic Cosmos Laboratory, 2018-07-14) Hazra, Dhiraj Kumar; Paoletti, Daniela; Finelli, Fabio; Smoot, George F.We explore the constraints on the history of reionization from Planck 2015 CosmicMicrowave 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 additionalextra parameters with respect to the average optical depth used in the instantaneous reion-ization modeling. We investigate the degeneracies between the history of reionization andselected extensions of the standard cosmological model. In particular, we consider the de-generacies with the total mass of the neutrino sector and we discuss the possible correlationbetween the dark matter annihilation and the duration of reionization in the CMB. We usean extension to poly-reion model that was proposed in [1]. We compare the constraints fromPlanck 2015 data with the predicted constraints from possible future CMB mission as Lite-BIRD, and we also use the proposed CORE-like specifications as an example of what higherresolution can bring in addition. We find that the degeneracy between the averaged opticaldepth and the duration of reionization will be substantially removed by both concepts. De-generacies between the reionization history and either the total neutrino mass and propertiesof dark matter annihilation will also be improved by future surveys. We find only marginalimprovement in the constraints on reionization history for the higher resolution in the caseof long duration of reionization.Item Open Access Cosmic growth and expansion conjoined(2017-01-31) Linder, Eric V.; Linder, Eric V.Abstract Cosmological measurements of both the expansion history and growth history have matured, and the two together provide an important test of general relativity. We consider their joint evolutionary track, showing that this has advantages in distinguishing cosmologies relative to considering them individually or at isolated redshifts. In particular, the joint comparison relaxes the shape degeneracy that makes fσ8(z) curves difficult to separate from the overall growth amplitude. The conjoined method further helps visualization of which combinations of redshift ranges provide the clearest discrimination. We examine standard dark energy cosmologies, modified gravity, and “stuttering” growth, each showing distinct signatures.Item Open Access The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: Constraining modified gravity(American Physical Society, 2016-12-02) Mueller, Eva-Maria; Percival, Will; Linder, Eric; Alam, Shadab; Zhao, Gong-Bo; Sanchez, Ariel G.; Beutler, FlorianWe use baryon acoustic oscillation and redshift space distortion from the completed Baryon Oscillation Spectroscopic Survey, corresponding to data release 12 of the Sloan Digital Sky Survey, combined sample analysis in combination with the cosmic microwave background, supernova and redshift space distortion measurements from additional spectroscopic surveys to test deviations from general relativity. We present constraints on several phenomenological models of modified gravity.Item Open Access Λ is Coming: Parametrizing Freezing Fields(NURIS; Energetic Cosmos Laboratory, 2018-03-21) Linder, Eric V.We explore freezing dark energy, where the evolution of the field approaches that of a cosmological constant at late times. We propose two general, two-parameter forms to describe the class of freezing field models, in analogy to ones for thawing fields, here based on the physics of the flow parameter or the calibrated w-w′ phase space. Observables such as distances and Hubble parameters are fit to within 0.1%, and the dark energy equation of state generally to within better than 1%, of the exact numerical solutions.Item Open Access Cosmic Growth Signatures of Modified Gravitational Strength(NURIS; Energetic Cosmos Laboratory, 2018-09-05) Denissenya, Mikhail; Linder, Eric V.Cosmic growth of large scale structure probes the entire history of cosmic expansion and gravitational coupling. To get a clear picture of the effects of modification of gravity we consider a deviation in the coupling strength (effective Newton’s constant) at different redshifts, with different durations and amplitudes. We derive, analytically and numerically, the impact on the growth rate and growth amplitude. Galaxy redshift surveys can measure a product of these through redshift space distortions and we connect the modified gravity to the observable ina way that may provide a useful parametrization of the ability of future surveys to test gravity. In particular, modifications during the matter-dominated era can be treated by a single parameter, the “area” of the modification, to an accuracy of∼0.3% in the observables. We project constraints on both early and late time gravity for the Dark Energy Spectroscopic Instrument and discuss what is needed for tightening tests of gravity to better than 5% uncertaintyItem Open Access Constraining dark energy dynamics in extended parameter space(American Physical Society, 2017-07-19) Di Valentino, Eleonora; Melchiorri, Alessandro; Linder, Eric V.; Silk, JosephDynamical dark energy has been recently suggested as a promising and physical way to solve the 3 sigma tension on the value of the Hubble constant H0 between the direct measurement of Riess et al. (2016) (R16, hereafter) and the indirect constraint from cosmic microwave anisotropies obtained by the Planck satellite under the assumption of a ΛCDM model. In this paper, by parametrizing dark energy evolution using the w0−wa approach, and considering a 12 parameter extended scenario, we find that: (a) the tension on the Hubble constant can indeed be solved with dynamical dark energy, (b) a cosmological constant is ruled out at more than 95% c.l. by the Planck+R16 dataset, and (c) all of the standard quintessence and half of the “downward going” dark energy model space (characterized by an equation of state that decreases with time) is also excluded at more than 95% c.l. These results are further confirmed when cosmic shear, CMB lensing, or SN Ia luminosity distance data are also included. The best fit value of the χ2 for the Planck+R16 data set improves by Δχ2=−12.9 when moving to 12 parameters respect to standard ΛCDM. However, tension remains with the BAO dataset. A cosmological constant and small portion of the freezing quintessence models are still in agreement with the Planck+R16+BAO data set at between 68% and 95% c.l. Conversely, for Planck plus a phenomenological H0 prior, both thawing and freezing quintessence models prefer a Hubble constant of less than 70 km/s/Mpc. The general conclusions hold also when considering models with nonzero spatial curvature.Item Open Access Accelerated Parameter Estimation with DALE X(NURIS; Energetic Cosmos Laboratory, 2017-05-08) Daniel, Scott F.; Linder, Eric V.We consider methods for improving the estimation of constraints on a high-dimensional parameter space with a computationally expensive likelihood function. In such cases Markov chain Monte Carlo (MCMC) can take a long time to converge and concentrates on finding the maxima rather than the often-desired confidence con-tours for accurate error estimation. We employ DALEχ(Direct Analysis of Limits via the Exterior ofχ2) for determining confidence contours by minimizing a cost function parametrized to incentivize points in parameter space which are both on the confidence limit and far from previously sampled points. We compare DALEχ to the nested sampling algorithm implemented in MultiNest on a toy likelihood function that is highly non-Gaussian and non-linear in the mapping between parameter values and χ2. We find that in high-dimensional cases DALEχfinds the same confidence limit as Multi-Nest using roughly an order of magnitude fewer evaluations of the likelihood function.DALE χ is open-source and available athttps://github.com/danielsf/Dalex.git.Item Open Access Slicing the vacuum: New accelerating mirror solutions of the dynamical Casimir effect(American Physical Society, 2017-12-22) Good, Michael R.R.; Linder, Eric V.Radiation from accelerating mirrors in a Minkowski spacetime provides insights into the nature of horizons, black holes, and entanglement entropy. We introduce new, simple, symmetric and analytic moving mirror solutions and study their particle, energy, and entropy production. This includes an asymptotically static case with finite emission that is the black hole analog of complete evaporation. The total energy, total entropy, total particles, and spectrum are the same on both sides of the mirror. We also study its asymptotically inertial, drifting analog (which gives a black hole remnant) to explore differences in finite and infinite production.Item Open Access Witnessing the reionization history using Cosmic Microwave Background observation from Planck(NURIS; Energetic Cosmos Laboratory, 2017-12-11) Hazra, Dhiraj Kumar; Smoot, George FWe constrain the history of reionization using the data from Planck 2015 Cosmic Microwave Background (CMB) temperature and polarization anisotropy observations. We also use prior constraints on the reionization history at redshifts ∼7−8 obtained from Lyman-α emission observations. Using the free electron fractions at different redshifts as free parameters, we construct the complete reionization history using polynomials. Our construction provides an extremely flexible framework to search for the history of reionization as a function of redshifts. We present a conservative and an optimistic constraint on reionization that are categorized by the flexibilities of the models and datasets used to constrain them, and we report that CMB data marginally favors extended reionization histories. In both the cases, we find the mean values of optical depth to be larger (≈0.09 and 0.1) than what we find in standard steplike reionization histories (0.079±0.017). At the same time we also find that the maximum free electron fraction allowed by the data for redshifts more than 15 is ∼0.25 at 95.4\% confidence limit in the case of optimistic constraint.Item Open Access Subpercent Accurate Fitting of Modified Gravity Growth(NURIS; Energetic Cosmos Laboratory, 2017-09-25) Denissenya, Mikhail; Linder, Eric V.Adding to our previous method for dealing with gravitational modifications at redshiftz&3through a single parameter, we investigate treatment of lower redshift modifications to linear growth observables. We establish sub percent accurate fits to the redshift space distortion observablefσ8(a)using two parameters binned in redshift, testing the results for modifications with time dependence that rises, falls, is nonmonotonic, is multipeaked, and corresponds to f(R) and braneworld gravity. The residuals are then propagated to cosmological parameter biases for DESI observations, and found to cause a shift in the dark energy joint confidence contour by less than the equivalent of∼0.1σ. The proposed 2–3 parameter modified gravity description also can reveal physical characteristics of the underlying theory.Item Open Access Probing features in inflaton potential and reionization history with future CMB space observations(NURIS; Energetic Cosmos Laboratory, 2018-03-04) Hazra, Dhiraj Kumar; Paoletti, Daniela; Ballardini, Mario; Finelli, Fabio; Shafieloo, Arman; Smoot, George F; Starobinsky, Alexei A.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.Item Open Access Vacuum phase transition solves the H0 tension(American Physical Society, 2018-02-23) Di Valentino, Eleonora; Linder, Eric V.Taking the Planck cosmic microwave background data and the more direct Hubble constant measurement data as unaffected by systematic offsets, the values of the Hubble constant $H_0$ interpreted within the $\Lambda$CDM cosmological constant and cold dark matter cosmological model are in $\sim 3.3 \sigma$ tension. We show that the Parker vacuum metamorphosis model, physically motivated by quantum gravitational effects and with the same number of parameters as $\Lambda$CDM, can remove the $H_0$ tension, and can give an improved fit to data (up to $\Delta\chi^2=-7.5$). It also ameliorates tensions with weak lensing data and the high redshift Lyman alpha forest data. We separately consider a scale dependent scaling of the gravitational lensing amplitude, such as provided by modified gravity, neutrino mass, or cold dark energy, motivated by the somewhat different cosmological parameter estimates for low and high CMB multipoles. We find that no such scale dependence is preferred.Item Open Access Eternal and Evanescent Black Holes: It’s All Done With Mirrors(NURIS; Energetic Cosmos Laboratory, 2017-11-27) Good, Michael R.R.; Linder, Eric V.The analogy between black hole radiation and accelerating mirror radiation (the dynamical Casimir effect) is particularly strong for mirror trajectories giving rise to a constant thermal flux of particles. We present new ways to achieve such thermal plateaus, and customize their finite, semi-infinite, and eternal presence, corresponding to forming/collapsing, complete-evaporation/remnants,and eternal black holes. We find simple expressions for the energy flux in terms of the mirror rapidity as a function of proper time and null time.Item Open Access No Slip Gravity(NURIS; Energetic Cosmos Laboratory, 2018-01-04) Linder, Eric V.A subclass of the Horndeski modified gravity theory we call No Slip Gravity has particularly interesting properties: 1) a speed of gravitational wave propagation equal to the speed of light, 2) equality between the effective gravitational coupling strengths to matter and light, G matter and G light, hence no slip between the metric potentials, yet difference from Newton's constant, and 3) suppressed growth to give better agreement with galaxy clustering observations. We explore the characteristics and implications of this theory, and project observational constraints. We also give a simple expression for the ratio of the gravitational wave standard siren distance to the photon standard candle distance, in this theory and others, and enable a direct comparison of modified gravity in structure growth and in gravitational waves, an important crosscheck.Item Open Access Cosmic Curvature Tested Directly from Observations(NURIS; Energetic Cosmos Laboratory, 2018-02-13) Denissenya, Mikhail; Linder, Eric V.; Shafieloo, ArmanCosmic spatial curvature is a fundamental geometric quantity of the Universe. We investigate a model independent, geometric approach to measure spatial curvature directly from observations,without any derivatives of data. This employs strong lensing time delays and supernova distance measurements to measure the curvature itself, rather than just testing consistency with flatness.We define two curvature estimators, with differing error propagation characteristics, that can cross-check each other, and also show how they can be used to map the curvature in redshift slices, totest constancy of curvature as required by the Robertson-Walker metric. Simulating realizations ofredshift distributions and distance measurements of lenses and sources, we estimate uncertainties onthe curvature enabled by next generation measurements. Theresults indicate that the model independent methods, using only geometry without assuming forms for the energy density constituents,can determine the curvature at the∼6×10^−3 level.Item Open Access Reinterpreting Low Frequency LIGO/Virgo Events as Magnified Stellar-Mass Black Holes at Cosmological Distances(NURIS; Energetic Cosmos Laboratory, 2018-02-14) Broadhurst, Tom; Diego, Jose M.; Smoot III, GeorgeGravitational 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.Item Open Access Dark Energy from α-attractors: Phenomenology and Observational Constraints(NURIS; Energetic Cosmos Laboratory, 2018-03-01) Garcia-Garcia, Carlos; Linder, Eric V.; Ruiz-Lapuente, Pilar; Zumalacaregui, MiguelThe possibility of linking inflation and late cosmic accelerated expansion using the α-attractor models has received increasing attention due to their physical motivation. In the early universe, α-attractors provide an inflationary mechanism compatible with Planck satellite CMB observations and predictive for future gravitational wave CMB modes. Additionally α-attractors can be written as quintessence models with a potential that connects a power law regime with a plateau or uplifted exponential, allowing a late cosmic accelerated expansion that can mimic behavior near a cosmological constant. In this paper we study a generalized dark energy α-attractor model. We thoroughly investigate its phenomenology, including the role of all model parameters and the possibility of large-scale tachyonic instability clustering. We verify the relation that 1+w∼1/α (while the gravitational wave power r∼α) so these models predict that a signature should appear in either the primordial B-modes or in late time deviation from a cosmological constant. We constrain the model parameters with current datasets, including the cosmic microwave background (Planck 2015 compressed likelihood), baryon acoustic oscillations (BOSS DR12) and supernovae (Pantheon compressed). Our results show that expansion histories close to a cosmological constant exist in large regions of the parameter space, not requiring a fine-tuning of the parameters or initial conditions.Item Open Access The Well-Tempered Cosmological Constant(NURIS; Energetic Cosmos Laboratory, 2018-05-01) Appleby, Stephen; Linder, Eric V.Self tuning is one of the few methods for dynamically cancelling a large cosmological constantand yet giving an accelerating universe. Its drawback is that it tends to screen all sources of energydensity, including matter. We develop a model that tempers the self tuning so the dynamical scalarfield still cancels an arbitrary cosmological constant, including the vacuum energy through any highenergy phase transitions, without affecting the matter fields. The scalar-tensor gravitational actionis simple, related to cubic Horndeski gravity, with a nonlinear derivative interaction plus a tadpoleterm. Applying shift symmetry and using the property of degeneracy of the field equations we findfamilies of functions that admit de Sitter solutions with expansion rates that are independent ofthe magnitude of the cosmological constant and preserve radiation and matter dominated phases. That is, the method can deliver a standard cosmic history including current acceleration, despite the presence of a Planck scale cosmological constant.