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DOE OSTI2013

Supernova constraints on multi-coupled dark energy

The persisting consistency of ever more accurate observational data with the predictions of the standard ΛCDM cosmological model puts severe constraints on possible alternative scenarios, but still does not shed any light on the fundamental nature of the cosmic dark sector. As large deviations from a ΛCDM cosmology are ruled out by data, the path to detect possible features of alternative models goes necessarily through the definition of cosmological scenarios that leave almost unaffected the background and — to a lesser extent — the linear perturbations evolution of the universe. In this context, the Multi-coupled DE (McDE) model was proposed by Baldi [9] as a particular realization of an interacting Dark Energy field characterized by an effective screening mechanism capable of suppressing the effects of the coupling at the background and linear perturbation level. In the present paper, for the first time, we challenge the McDE scenario through a direct comparison with real data, in particular with the luminosity distance of Type Ia supernovae. By studying the existence and stability conditions of the critical points of the associated background dynamical system, we select only the cosmologically consistent solutions, and confront their background expansion history with data. Confirming previous qualitative results, the McDE scenario appears to be fully consistent with the adopted sample of Type Ia supernovae, even for coupling values corresponding to an associated scalar fifth-force about four orders of magnitude stronger than standard gravity. Our analysis demonstrates the effectiveness of the McDE background screening, and shows some new non-trivial asymptotic solutions for the future evolution of the universe. Clearly, linear perturbation data and, even more, nonlinear structure formation properties are expected to put much tighter constraints on the allowed coupling range. Nonetheless, our results show how the background expansion history might be highly insensitive to the fundamental nature and to the internal complexity of the dark sector.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

Maps of CMB lensing deflection from N-body simulations in Coupled Dark Energy Cosmologies

We produce lensing potential and deflection-angle maps in order to simulate the weak gravitational lensing of the Cosmic Microwave Background (CMB) via ray-tracing through the COupled Dark Energy Cosmological Simulations (CoDECS), the largest suite of N-body simulations to date for interacting Dark Energy cosmologies. The constructed maps faithfully reflect the N-body cosmic structures on a range of scales going from the arcminute to the degree scale, limited only by the resolution and extension of the simulations. We investigate the variation of the lensing pattern due to the underlying Dark Energy (DE) dynamics, characterised by different background and perturbation behaviours as a consequence of the interaction between the DE field and Cold Dark Matter (CDM). In particular, we study in detail the results from three cosmological models differing in the background and perturbations evolution at the epoch in which the lensing cross section is most effective, corresponding to a redshift of ∼ 1, with the purpose to isolate their imprints in the lensing observables, regardless of the compatibility of these models with present constraints. The scenarios investigated here include a reference ΛCDM cosmology, a standard coupled DE (cDE) scenario, and a ''bouncing'' cDE scenario. For the standard cDE scenario, we find that typical differences in the lensing potential result from two effects: the enhanced growth of linear CDM density fluctuations with respect to the ΛCDM case, and the modified nonlinear dynamics of collapsed structures induced by the DE-CDM interaction. As a consequence, CMB lensing highlights the DE impact in the cosmological expansion, even in the degenerate case where the amplitude of the linear matter density perturbations, parametrised through σ{sub 8}, is the same in both the standard cDE and ΛCDM cosmologies. For the ''bouncing'' scenario, we find that the two opposite behaviours of the lens density contrast and of the matter abundance lead to a counter-intuitive effect, making the power of the lensing signal in this model lower by 10% than in the ΛCDM scenario. Moreover, we compare the behaviour of CDM and baryons in CoDECS separately, in order to isolate effects coming from the coupling with the DE component. We find that, in the bouncing scenario, baryons show an opposite trend with respect to CDM, due to the coupling of the latter with the DE component. These results confirm the relevance of CMB lensing as a probe for DE at the early stages of cosmic acceleration, and demonstrate the reliability of N-body based large scale CMB lensing simulations in the context of DE studies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

Inflationary magnetogenesis without the strong coupling problem

The simplest gauge invariant models of inflationary magnetogenesis are known to suffer from the problems of either large backreaction or strong coupling, which make it difficult to self-consistently achieve cosmic magnetic fields from inflation with a field strength larger than 10{sup −32}G today on the Mpc scale. Such a strength is insufficient to act as seed for the galactic dynamo effect, which requires a magnetic field larger than 10{sup −20}G. In this paper we analyze simple extensions of the minimal model, which avoid both the strong coupling and back reaction problems, in order to generate sufficiently large magnetic fields on the Mpc scale today. First we study the possibility that the coupling function which breaks the conformal invariance of electromagnetism is non-monotonic with sharp features. Subsequently, we consider the effect of lowering the energy scale of inflation jointly with a scenario of prolonged reheating where the universe is dominated by a stiff fluid for a short period after inflation. In the latter case, a systematic study shows upper bounds for the magnetic field strength today on the Mpc scale of 10{sup −13}G for low scale inflation and 10{sup −25}G for high scale inflation, thus improving on the previous result by 7-19 orders of magnitude. These results are consistent with the strong coupling and backreaction constraints.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

New limits on coupled dark energy from Planck

Recently, the Planck collaboration has released the first cosmological papers providing the high resolution, full sky, maps of the cosmic microwave background (CMB) temperature anisotropies. It is crucial to understand that whether the accelerating expansion of our universe at present is driven by an unknown energy component (Dark Energy) or a modification to general relativity (Modified Gravity). In this paper we study the coupled dark energy models, in which the quintessence scalar field nontrivially couples to the cold dark matter, with the strength parameter of interaction β. Using the Planck data alone, we obtain that the strength of interaction between dark sectors is constrained as β < 0.102 at 95% confidence level, which is tighter than that from the WMAP9 data alone. Combining the Planck data with other probes, like the Baryon Acoustic Oscillation (BAO), Type-Ia supernovae ''Union2.1 compilation'' and the CMB lensing data from Planck measurement, we find the tight constraint on the strength of interaction β < 0.052 (95% C.L.). Interestingly, we also find a non-zero coupling β = 0.078±0.022 (68% C.L.) when we use the Planck, the ''SNLS'' supernovae samples, and the prior on the Hubble constant from the Hubble Space Telescope (HST) together. This evidence for the coupled dark energy models mainly comes from a tension between constraints on the Hubble constant from the Planck measurement and the local direct H{sub 0} probes from HST.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Dark matter as a Bose-Einstein Condensate: the relativistic non-minimally coupled case

Bose-Einstein Condensates have been recently proposed as dark matter candidates. In order to characterize the phenomenology associated to such models, we extend previous investigations by studying the general case of a relativistic BEC on a curved background including a non-minimal coupling to curvature. In particular, we discuss the possibility of a two phase cosmological evolution: a cold dark matter-like phase at the large scales/early times and a condensed phase inside dark matter halos. During the first phase dark matter is described by a minimally coupled weakly self-interacting scalar field, while in the second one dark matter condensates and, we shall argue, develops as a consequence the non-minimal coupling. Finally, we discuss how such non-minimal coupling could provide a new mechanism to address cold dark matter paradigm issues at galactic scales.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Fluctuations in strongly coupled cosmologies

In the early Universe, a dual component made of coupled CDM and a scalar field Φ, if their coupling β > (3){sup 1/2}/2, owns an attractor solution, making them a stationary fraction of cosmic energy during the radiation dominated era. Along the attractor, both such components expand ∝a{sup −4} and have early density parameters Ω{sub d} = 1/(4β{sup 2}) and Ω{sub c} = 2 Ω{sub d} (field and CDM, respectively). In a previous paper it was shown that, if a further component, expanding ∝a{sup −3}, breaks such stationary expansion at z ∼ 3–5 × 10{sup 3}, cosmic components gradually acquire densities consistent with observations. This paper, first of all, considers the case that this component is warm. However, its main topic is the analysis of fluctuation evolution: out of horizon modes are then determined; their entry into horizon is numerically evaluated as well as the dependence of Meszaros effect on the coupling β; finally, we compute: (i) transfer function and linear spectral function; (ii) CMB C{sub l} spectra. Both are close to standard ΛCDM models; in particular, the former one can be so down to a scale smaller than Milky Way, in spite of its main DM component being made of particles of mass < 1 keV. The previously coupled CDM component, whose present density parameter is O(10{sup −3}), exhibits wider fluctuations δρ/ρ, but approximately β-independent δρ values. We discuss how lower scale features of these cosmologies might ease quite a few problems that ΛCDM does not easily solve.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Anisotropy in inflation with non-minimal coupling

We study a new anisotropic inflation model, with an inflaton field nonminimally coupled with the gravity and a vector field. We find that the anisotropic attractor solution exists not only in the weak curvature coupling limit, but more interestingly in the strong curvature coupling limit as well. We show that in the strong curvature coupling limit, the contribution from the anisotropy is greatly suppressed.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

The observational position of simple non-minimally coupled inflationary scenarios

We consider two classes of non-minimally coupled inflation models; those with a quadratic coupling of the inflaton to gravity, and the 'Universal Attractor' models where the coupling is connected to the potential. We make a detailed analysis of the attractor structure in the latter case, identifying a shift of the attractor from the Starobinsky point and determining conditions for approach to the attractor. We then assess the viability of the models under different interpretations of the BICEP2 experiment's detection of B-mode polarisation, finding strong constraints on the non-minimal coupling in the case where the B-modes have mostly primordial origin.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

On the importance of nonlinear couplings in large-scale neutrino streams

We propose a procedure to evaluate the impact of nonlinear couplings on the evolution of massive neutrino streams in the context of large-scale structure growth. Such streams can be described by general nonlinear conservation equations, derived from a multiple-flow perspective, which generalize the conservation equations of non-relativistic pressureless fluids. The relevance of the nonlinear couplings is quantified with the help of the eikonal approximation applied to the subhorizon limit of this system. It highlights the role played by the relative displacements of different cosmic streams and it specifies, for each flow, the spatial scales at which the growth of structure is affected by nonlinear couplings. We found that, at redshift zero, such couplings can be significant for wavenumbers as small as k=0.2 h/Mpc for most of the neutrino streams.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Fitting and forecasting coupled dark energy in the non-linear regime

We consider cosmological models in which dark matter feels a fifth force mediated by the dark energy scalar field, also known as coupled dark energy. Our interest resides in estimating forecasts for future surveys like Euclid when we take into account non-linear effects, relying on new fitting functions that reproduce the non-linear matter power spectrum obtained from N-body simulations. We obtain fitting functions for models in which the dark matter-dark energy coupling is constant. Their validity is demonstrated for all available simulations in the redshift range 0z=–1.6 and wave modes below 0k=1 h/Mpc. These fitting formulas can be used to test the predictions of the model in the non-linear regime without the need for additional computing-intensive N-body simulations. We then use these fitting functions to perform forecasts on the constraining power that future galaxy-redshift surveys like Euclid will have on the coupling parameter, using the Fisher matrix method for galaxy clustering (GC) and weak lensing (WL). We find that by using information in the non-linear power spectrum, and combining the GC and WL probes, we can constrain the dark matter-dark energy coupling constant squared, β{sup 2}, with precision smaller than 4% and all other cosmological parameters better than 1%, which is a considerable improvement of more than an order of magnitude compared to corresponding linear power spectrum forecasts with the same survey specifications.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Cosmological constraints on coupled dark energy

The coupled dark energy model provides a possible approach to mitigate the coincidence problem of cosmological standard model. Here, the coupling term is assumed as Q-bar = 3 H ξ {sub x} ρ-bar {sub x} , which is related to the interaction rate and energy density of dark energy. We derive the background and perturbation evolution equations for several coupled models. Then, we test these models by currently available cosmic observations which include cosmic microwave background radiation from Planck 2015, baryon acoustic oscillation, type Ia supernovae, f σ{sub 8}( z ) data points from redshift-space distortions, and weak gravitational lensing. The constraint results tell us there is no evidence of interaction at 2σ level, it is very hard to distinguish different coupled models from other ones.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Electroweak stability and non-minimal coupling

The measured values of the Higgs and top quark mass indicate that the electroweak vacuum is metastable if there is no new physics below the Planck scale. This is at odds with a period of high scale inflation. A non-minimal coupling between the Higgs field and the Ricci scalar can stabilize the vacuum as it generates a large effective Higgs mass during inflation. We consider the effect of this coupling during preheating, when Higgs modes can be produced very efficiently due to the oscillating Ricci scalar. We compute their effect on the effective potential and the energy density. The Higgs excitations are defined with respect to the adiabatic vacuum. We study the adiabaticity conditions and find that the dependence of our results on the choice of the order of the adiabatic vacuum increases with time. For large enough coupling particle production is so efficient that the Higgs decays to the true vacuum before this is an issue. However, for smaller values of the Higgs-curvature coupling no definite statements can be made as the vacuum dependence is large.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Phase-controlled improvement of photon lifetime in coupled superconducting cavities

High-quality cavities are crucial for various fundamental physical studies and applications. Here we find that by coupling two cavities directly or via a phase-tunable coupling channel, the photon lifetime of the local field can exceed that of the bare cavities. The cavity photon lifetime is modified by the phases of the initial states and the phase accumulation on the coupling channel, which affect the interference between cavities. In experiments, by coupling superconducting radio-frequency cavities via phase-tunable cables, we realize a factor of 2 improvement in the cavity photon lifetime. The results can bring rich revenue to quantum information science, sensing, and high-energy physics.

43 PARTICLE ACCELERATORS↗

DOE OSTI2019

Disentangling spin-orbit coupling and local magnetism in a quasi-two-dimensional electron system

Quantum interference between time-reversed electron paths in two dimensions (2D) leads to the well-known weak localization correction to resistance. If spin-orbit coupling is present, the resistance correction is negative, termed weak antilocalization (WAL). Here, we report the observation of WAL coexisting with exchange coupling between itinerant electrons and localized magnetic moments. We use low-temperature magnetotransport measurements to investigate the quasi-two-dimensional, high-electron-density interface formed between SrTiO 3 and the antiferromagnetic Mott insulator NdTiO 3 . As the magnetic field angle is gradually tilted away from the sample normal, the data reveal the interplay between strong k-cubic Rashba-type spin-orbit coupling and a substantial magnetic exchange interaction from local magnetic regions. The resulting quantum corrections to the conduction are in excellent agreement with existing models and allow sensitive determination of the small magnetic moments (22 μ B on average), their magnetic anisotropy, and mutual coupling strength. Furthermore, this effect is expected to arise in other 2D magnetic materials systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

Anisotropic superconductivity mediated by ferroelectric fluctuations in cubic systems with spin-orbit coupling

Motivated by the experimental observation that superconductivity in bulk doped SrTiO 3 is enhanced as a putative ferroelectric quantum critical point (FE-QCP) is approached, we study the pairing instability of a cubic system in which electrons exchange low-energy ferroelectric fluctuations. Instead of the gradient coupling to the lattice distortion associated with ferroelectricity, we consider direct coupling between the electrons and the bosonic ferroelectric field that appears in the presence of spin-orbit coupling. Working in the weak-coupling regime, we find that the pairing interaction is dominated by the soft transverse optical (TO) mode, resulting in a Tc enhancement upon approaching the FE-QCP. Focusing on even-parity states, we find that although the s-wave state always wins, states with higher Cooper-pair angular momentum become close competitors as the TO mode softens. We show that the cubic anisotropy of the FE fluctuations mixes the s-wave and g-wave states, resulting in a characteristic anisotropy of the gap function. Here, the gap anisotropy behaves nonmonotonically as the FE-QCP is approached: upon decreasing the TO mode frequency, the gap anisotropy first changes sign and then increases in magnitude. We discuss the possible applications of our results to the superconducting state of SrTiO 3 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Spin-orbit coupled systems in the atomic limit: rhenates, osmates, iridates

Motivated by RIXS experiments on a wide range of complex heavy oxides, including rhenates, osmates, and iridates, we discuss the theory of RIXS for site-localized t 2 g orbital systems with strong spin-orbit coupling. For such systems, we present exact diagonalization results for the spectrum at different electron fillings, showing that it accesses “single-particle” and “multiparticle” excitations. This leads to a simple picture for the energies and intensities of the RIXS spectra in Mott insulators such as double perovskites which feature highly localized electrons, and yields estimates of the spin-orbit coupling and Hund's coupling in correlated 5d oxides. We present new higher resolution RIXS data at the Re L 3 edge in Ba 2 YReO 6 which finds a previously unresolved peak splitting, providing further confirmation of our theoretical predictions. Using ab initio electronic structure calculations on Ba 2 MReO 6 (with M=Re, Os, Ir) we show that while the atomic limit yields a reasonable effective Hamiltonian description of the experimental observations, effects such as t 2 g –e g interactions and hybridization with oxygen are important. Our ab initio estimate for the strength of the intersite exchange coupling shows that, compared to the d 3 systems, the exchange is one or two orders of magnitude weaker in the d 2 and d 4 materials, which may partly explain the suppression of long-range magnetic order in the latter compounds. As a way to interpolate between the site-localized picture and our electronic structure band calculations, we discuss the spin-orbital levels of the MO 6 cluster. In conclusion, this suggests a possible role for intracluster excitons in Ba 2 YIrO 6 which may lead to a weak breakdown of the atomic J eff = 0 picture and to small magnetic moments.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2019

Two-level system coupled to phonons: Full analytical solution

In this study, we propose an analytical procedure to fully solve a two-level system coupled to phonons. Instead of using the common formulation in terms of linear and quadratic system-phonon couplings, we introduce different phonons depending on the system electronic level. We use this approach to recover known results for the linear-coupling limit in a simple way. More importantly, we derive results for the quadratic coupling induced by a phonon frequency change, a problem considered up to now as not analytically solvable.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Spin-lattice coupling in magnetocaloric Gd 5 ( Ge , Si ) 4 alloys by $in$ $situ$ x-ray pair distribution analysis in magnetic field

Here, using in situ x-ray pair distribution analysis in magnetic field, we study the strong spin-lattice coupling in archetypal magnetocaloric Gd 5 (Ge,Si) 4 alloys manifested by the presence of a first order paramagnetic (PM)-to-ferromagnetic (FM) phase transition that can be triggered by either decreasing temperature in zero magnetic field or increasing magnetic field at constant temperature. We find that the coupling arises from the tendency of Gd-(Si,Ge) slabs in the alloys to reversibly slide against each other to both pack closely and couple ferromagnetically. We also find that, locally, the packing of slabs in FM phases induced by decreasing temperature in zero field is different from that in FM phases of the same chemical composition induced by increasing magnetic field isothermally, indicating that temperature and magnetic field are coupled but not necessarily equivalent control variables for triggering phase transitions in strongly correlated systems.

36 MATERIALS SCIENCE↗