Peaks In Power Spectrum Research Articles

Improving constraints on models addressing the Hubble tension with CMB delensing

The Hubble Tension is a well-known issue in modern cosmology that refers to the apparent disagreement in inferences of the Hubble constant H 0 as found through low-redshift observations and those derived from the ΛCDM model utilizing early universe observations. Several extensions to ΛCDM have been proposed to address the Hubble Tension that involve new ingredients or dynamics in the early universe. Reversing the effects of gravitational lensing on cosmic microwave background (CMB) maps produces sharper acoustic peaks in power spectra and allows for tighter constraints on cosmological parameters. We investigate the efficacy of CMB delensing for improving the constraints on parameters used in extensions of the ΛCDM model that are aimed at resolving the Hubble Tension (such as varying fundamental constants, contributions from early dark energy, and self-interacting dark radiation). We use Fisher forecasting to predict the expected constraints with and without this delensing procedure. We demonstrate that CMB delensing improves constraints on H 0 by ∼ 20% for viable models and significantly improves constraints on parameters across the board in the low-noise regime.

Placental assessment using spectral analysis of the envelope of umbilical venous waveforms in sheep

IntroductionThis study was designed to test the efficacy of an ultrasound flow measurement method to evaluate placental function in a hyperandrogenic sheep model that produces placental morphologic changes and an intrauterine growth restriction (IUGR) phenotype. Materials and methodsPregnant ewes were assigned randomly between control (n = 12) and testosterone-treatment (T-treated, n = 22) groups. The T-treated group was injected twice weekly intramuscularly (IM) with 100 mg testosterone propionate. Control sheep were injected with corn oil vehicle. Lambs were delivered at 119.5 ± 0.48 days gestation. At the time of delivery of each lamb, flow spectra were generated from one fetal artery and two fetal veins, and the spectral envelopes examined using fast Fourier transform analysis. Base 10 logarithms of the ratio of the amplitudes of the maternal and fetal spectral peaks (LRSP) in the venous power spectrum were compared in the T-treated and control populations. In addition, we calculated the resistive index (RI) for the artery defined as ((peak systole – min diastole)/peak systole). Two-tailed T-tests were used for comparisons. ResultsLRSPs, after removal of significant outliers, were −0.158 ± 0.238 for T-treated and 0.057 ± 0.213 for control (p = 0.015) animals. RIs for the T-treated sheep fetuses were 0.506 ± 0.137 and 0.497 ± 0.086 for controls (p = 0.792) DiscussionLRSP analysis distinguishes between T-treated and control sheep, whereas RIs do not. LRSP has the potential to identify compromised pregnancies.

Multi-field inflation with large scalar fluctuations: non-Gaussianity and perturbativity

Recently multi-field inflation models that can produce large scalar fluctuations on small scales have drawn a lot of attention, primarily because they could lead to primordial black hole production and generation of large second-order gravitational waves. In this work, we focus on models where the scalar fields responsible for inflation live on a hyperbolic field space. In this case, geometrical destabilisation and non-geodesic motion are responsible for the peak in the scalar power spectrum. We present new results for scalar non-Gaussianity and discuss its dependence on the model's parameters. On scales around the peak, we typically find that the non-Gaussianity is large and close to local in form. We validate our results by employing two different numerical techniques, utilising the transport approach, based on full cosmological perturbation theory, and the δN formalism, based on the separate universe approximation. We discuss implications of our results for the perturbativity of the underlying theory, focusing in particular on versions of these models with potentially relevant phenomenology at interferometer scales.

Primordial black holes and inflation from double-well potentials

We investigate the formation of large peaks in the inflationary curvature power spectrum from double-well potentials. In such scenarios, the initial CMB spectrum is created at large field values. Subsequently, the inflaton will cross one of the minima and will decelerate rapidly as it reaches the local maximum at the origin, either falling back or crossing it. During this final phase, a significant peak in the curvature power spectrum can be generated. Our analysis reveals that this class of models produces more pronounced peaks than most quasi-inflection point scenarios with less tuning for the model parameters. Finally, we construct an explicit theoretically motivated inflationary scenario that is consistent with the latest CMB observations and capable of generating sufficiently large curvature perturbations for primordial black holes.

Multiclustering needlet ILC for CMB B-mode component separation

ABSTRACT The Cosmic Microwave Background (CMB) primordial B-mode signal is predicted to be much lower than the polarized Galactic emission (foregrounds) in any region of the sky pointing to the need for sophisticated component separation methods. Among them, the blind Needlet Internal Linear Combination (NILC) has great relevance given our current poor knowledge of the B-mode foregrounds. However, the expected level of spatial variability of the foreground spectral properties complicates the NILC subtraction of the Galactic contamination. We therefore propose a novel extension of the NILC approach, the Multiclustering NILC (MC-NILC), which performs NILC variance minimization on separate regions of the sky (clusters) properly chosen to have similar spectral properties of the B-mode Galactic emission within them. Clusters are identified thresholding either the ratio of simulated foregrounds-only B modes (ideal case) or the one of cleaned templates of Galactic emission obtained from realistic simulations. In this work we present an application of MC-NILC to the future LiteBIRD satellite, which targets the observation of both reionization and recombination peaks of the primordial B-mode angular power spectrum with a total error on the tensor-to-scalar ratio δr < 0.001. We show that MC-NILC provides a CMB solution with residual foreground and noise contamination that is significantly lower than the NILC one and the primordial signal targeted by LiteBIRD at all angular scales for the ideal case and at the reionization peak for a realistic ratio. Thus, MC-NILC will represent a powerful method to mitigate B-mode foregrounds for future CMB polarization experiments.

Primordial black holes from single-field inflation: a fine-tuning audit

All single-field inflationary models invoke varying degrees of tuning in order to account for cosmological observations. Mechanisms that generate primordial black holes (PBHs) from enhancement of primordial power at small scales posit inflationary potentials that transiently break scale invariance and possibly adiabaticity over a range of modes. This requires additional tuning on top of that required to account for observations at scales probed by cosmic microwave background (CMB) anisotropies. In this paper we study the parametric dependence of various single-field models of inflation that enhance power at small scales and quantify the degree to which coefficients in the model construction have to be tuned in order for certain observables to lie within specified ranges. We find significant tuning: changing the parameters of the potentials by between one part in a hundred and one part in 108 (depending on the model) is enough to change the power spectrum peak amplitude by an order one factor. The fine-tuning of the PBH abundance is larger still by 1–2 orders of magnitude. We highlight the challenges imposed by this tuning on any given model construction. Furthermore, polynomial potentials appear to require significant additional fine-tuning to also match the CMB observations.

Primordial black hole production in natural and hilltop inflation

We consider the possibility of primordial black hole, PBH, formation sourced by a rise in the power spectrum. The power spectrum becomes large at late times due to decay of the inflaton into vectors through a ϕFF̃ coupling. Two background inflaton models which are well supported by current Planck data are considered, natural inflation and hilltop inflation. Many of the papers considering formation of PBHs have considered a peaked power spectrum where Pζ gets small again at late times. This avoids overproducing miniature PBHs which would evaporate and could violate BBN and CMB bounds. This paper examines the other way of avoiding these bounds, producing PBHs from perturbations formed closer to the end of inflation such that the PBHs are too small to violate these bounds. This has the advantage of allowing for simpler models in that no additional feature is needed to be added to evade constraints. Although these black holes would have evaporated, they can be close to without exceeding current BBN bounds, making it possible the signature will be revealed in the future. We calculate how the various model parameters affect the mass and number of PBHs produced. Any evidence for PBHs sourced from an inflationary power spectrum would provide evidence for inflation on a drastically different energy scale from the CMB, and thus would be highly valuable in answering what occurred during inflation.

Measurement of the matter-radiation equality scale using the extended baryon oscillation spectroscopic survey quasar sample

ABSTRACT The position of the peak of the matter power spectrum, the so-called turnover scale, is set by the horizon size at the epoch of matter-radiation equality. It can easily be predicted in terms of the physics of the universe in the relativistic era, and so can be used as a standard ruler, independent of other features present in the matter power spectrum, such as baryon acoustic oscillations (BAOs). We use the distribution of quasars measured by the extended Baryon Oscillation Spectroscopic Survey (eBOSS) to determine the turnover scale in a model-independent fashion statistically. We avoid modelling the BAO by down-weighting affected scales in the covariance matrix using the mode deprojection technique. We measure the wavenumber of the peak to be $k_\mathrm{TO} = \left(17.6^{+1.9}_{-1.8} \right) \times 10^{-3}h/\mathrm{Mpc}$, corresponding to a dilation scale of $D_\mathrm{V}(z_\mathrm{eff} = 1.48) = \left(31.1^{+4.1}_{-3.4}\right)r_\mathrm{H}$. This is not competitive with current BAO distance measures in terms of determining the expansion history but does provide a useful cross-check. We combine this measurement with low-redshift distance measurements from type-Ia supernova data from Pantheon and BAO data from eBOSS to make a sound-horizon free estimate of the Hubble–Lemaître parameter and find it to be $H_0=64.8^{+8.4}_{-7.8} \ \mathrm{km/s/Mpc}$ with Pantheon, and $H_0=63.3^{+8.2}_{-6.9} \ \mathrm{km/s/Mpc}$ with eBOSS BAO. We make predictions for the measurement of the turnover scale by the Dark Energy Spectroscopic Instrument (DESI) survey, the Maunakea Spectroscopic Explorer (MSE), and MegaMapper, which will make more precise and accurate distance determinations.

Inflation from Multiple Pseudo-scalar Fields: Primordial Black Hole Dark Matter and Gravitational Waves

We study a model of inflation with multiple pseudo-scalar fields coupled to a U(1) gauge field through Chern–Simons interactions. Because of parity-violating interactions, one polarization of the gauge field is amplified, yielding to an enhanced curvature perturbation power spectrum. Inflation proceeds in multiple stages, as each pseudo-scalar field rolls toward its minimum, yielding to distinct multiple peaks in the curvature perturbation power spectra at various scales during inflation. The localized peaks in the power spectra generate primordial black holes that can furnish a large fraction of dark matter abundance. In addition, gravitational waves with nontrivial spectra are generated that are in the sensitivity ranges of various forthcoming GW observatories.

Investigation of the Cosmic evolution in the presence of non-relativistic neutrinos

The neutrinos of the early universe evolved from a relativistic phase at very early times to a massive particle behavior at later times. First, the kinetic energy of neutrinos is relativistic, and as a result, neutrinos can be described as massless particles. As the Universe expands, the temperature drops and the kinetic energy decreases, and the neutrinos turn into a non-relativistic phase with a non-negligible mass. In this paper, we first put constraints on the total mass of neutrinos. Then we investigate the effect of neutrinos on the CMB power spectrum, P(k), in the case of massless and massive neutrinos using the publicly available Boltzmann code CAMB and we prove that when neutrino coupled to scalar field the CMB power spectrum has a little shift, which means that the power spectrum of CMB is greatly affected by the background energy density and the accelerated expansion of the Universe. Furthermore, we investigate the effect of perturbed quintessence on this spectrum and find that the highest peaks of this spectrum are shifted to smaller scales. Also, we estimate the Deceleration–Acceleration(DA) redshift transition (z da) using the coupling canonical scalar field with neutrinos. For Pantheon data we obtain z da = 0.7 ± 0.05 and for CC data z da = 0.68 ± 0.03. In the presence of neutrinos the DA redshift transition is z da = 0.42 ± 0.03 for Pantheon data and z da = 0.49 ± 0.05 for CC data. These results indicate that neutrinos can affect this phase transition. The results obtained in this article show that when the mass of neutrinos increases, the value of the background energy density increases, resulting in a higher power spectrum peak. Also, by examining the effect of coupling neutrinos to dark energy, we find that the transition occurs at lower redshift.

Use of External Uterine Electromyography Across Stage I Labor.

Highly sensitive, external uterine electromyography (EMG) measures myometrial electrical activity and is noninvasive compared with the clinical intrauterine pressure catheter. Most experimental studies have measured EMG in 30-minute epochs, limiting the utility of this instrumentation in intrapartum clinical practice. To test proof of concept, surface uterine EMG contraction activity was continuously collected throughout the first stage of labor from healthy women at term gestation with (n = 3) and without (n = 1) epidural or combined spinal-epidural analgesia for a maximal length of 11 hours and 24 minutes. EMG activity was recorded concurrently with tocodynamometer (toco) signals, using a pair of electrodes on the left and right sides of the maternal umbilicus with grounds attached to both hips of the reclining woman in labor. The preamplifier cutoff frequency settings were appropriate to monitor smooth muscle contraction in labor, with the analog high-pass filter set at 0.05 Hz and the low-pass filter at 1.50 Hz. Signals were sampled at 100 Hz, transmitted to a computer, and visualized by Chart 4.2 software. EMG data from epochs at baseline, during the pre-epidural fluid bolus and at the 60-minute post-epidural test dose, and at 3, 5, 6, and 8 cm dilatation were analyzed for burst power spectrum peak frequency (Hz), burst power spectrum amplitude (mV2 ), and burst duration (seconds). Uterine EMG contractile bursts were preceded and followed by a stable baseline and coincided with toco contractions. Movement artifacts were negligible, and large movement artifacts were easily distinguishable. The EMG bursts and toco contractions remained clearly identifiable, even when one woman without epidural analgesia stood beside the bed laboring for approximately 10 minutes. Burst spectral components fell within the expected 0.34-to-1.00 Hz range for term labor. High-quality data demonstrate that EMG instrumentation effectively and accurately measures uterine contraction parameters across the first stage of term labor.

Anatomy of single-field inflationary models for primordial black holes

We construct an analytically solvable simplified model that captures the essential features for primordial black hole (PBH) production in most models of single-field inflation. The construction makes use of the Wands duality between the constant-roll (or slow-roll) and the preceding ultra-slow-roll phases and can be realized by a simple inflaton potential of two joined parabolas. Within this framework, it is possible to formulate explicit inflationary scenarios consistent with the CMB observations and copious production of PBHs of arbitrary mass. We quantify the variability of the shape of the peak in the curvature power spectrum in different inflationary scenarios and discuss its implications for probing PBHs with scalar-induced gravitational wave backgrounds. We find that the COBE/Firas μ-distortion constraints exclude the production of PBHs heavier than 104 M ⊙ in single-field inflation.

Cosmological imprints of SUSY breaking in models of sgoldstinoless non-oscillatory inflation

In supergravity, the dynamics of the sgoldstino – superpartner of the goldstino superfield associated with the breaking of supersymmetry at low energy – can substantially modify the dynamics of inflation in the primordial Universe. So-called sgoldstinoless models assume the existence of a nilpotency constraint S 2 = 0 that effectively removes the sgoldstino from the theory. Such models were proposed to realise non-oscillatory inflation scenarios with a single scalar field, which feature a long period of kination at the end of inflation, and therefore a non-standard post-inflationary cosmology. Using effective operators, we propose models in which the sgoldstino is stabilized close to the origin to reproduce the nilpotent constraint. We show that small sgoldstino fluctuations may lead to a sizeable back-reaction on the cosmological history. We study the effect of this back-reaction on the inflation observables measured in the cosmic microwave background and confront the model to a series of constraints including limits on ΔN eff. We show that the peculiar form of the potential in the large supersymmetry breaking scale limit can generate peaks in the scalar power spectrum produced from inflation. We study how certain perturbation modes may re-enter the horizon during or after kination and show that a large supersymmetry breaking scale may lead to the formation of primordial black holes with various masses in the early Universe.

Numerical investigation of noise suppression and amplification in forced oscillations of single and tandem cylinders in high Reynolds number turbulent flows

The noise generated by a three-dimensional turbulent wake behind an oscillating single or tandem cylinder(s) is studied using detached eddy simulation and the Ffowcs Williams-Hawkings (FW-H) method. This hybrid methodology is validated using some experimental data of a turbulent flow past a single or tandem stationary cylinder(s) and some numerical data (obtained from a direct numerical simulation) of a laminar flow past tandem oscillating cylinders. For an oscillating cylinder at a fixed Reynolds number Re=120,000, the sound energy is suppressed compared to that of a stationary cylinder provided the value of oscillation frequency approaches 57% of the original vortex-shedding frequency of the stationary cylinder. This noise reduction arises from the structural oscillations suppressing the noise generated by the vortex shedding from the stationary cylinder—the additional source of noise stemming from the structural oscillations is too small to compensate for the mechanism responsible for the noise suppression. The noise generated by the cylinder motion includes contributions from the loading and thickness noise, whereas the noise generated by vortex shedding from the stationary cylinder only includes the loading noise. The flow past tandem stationary cylinders exhibits a larger number of spectral peaks in the sound pressure power spectrum and the peaks occur at a lower frequency compared to the flow past a single cylinder. The drag force fluctuations result in the propagation of the sound pressure in the in-line direction, whereas the lift force fluctuations result in the propagation of the sound pressure in the transverse direction. Five different scenarios of stationary and/or oscillating tandem cylinders are studied. The second and third invariants of the velocity gradient tensor are used to visualize the distinct vortex structures in the wake for the five different scenarios of tandem cylinders. A single cylinder oscillating in the transverse direction exhibits a larger sound pressure level (SPL) than the streamwise oscillation of the same cylinder. In contrast, the streamwise (in-line) oscillation of one or the other cylinder in a tandem array results in a larger SPL than the transverse oscillation of one or the other cylinder. Finally, the SPL is more sensitive to the oscillations of the rear (downstream) cylinder than the front (upstream) cylinder.

Sensitivity enhancement in laser self-mixing nano-particle sizer with linear current tuning based frequency shifting method

Laser self-mixing interferometry (SMI) has been widely researched and applied to the field of traditional physical quantities (such as displacement, distance, velocity and vibration) detection due to the well-known merits of compact structure, low-cost and high sensitivity, additionally, it has also shown great potential in nano-particle sizing during the last two decades, primarily depending on the incoherent stochastic superposition of laser beam’s interaction with each particle in the illuminating volume, and the particle diameter can be determined from the power spectra of self-mixed signals through Lorentz fitting. SMI particle sensing generally uses constant current driving laser diodes (LD), so the power spectrum peak occurs around zero-frequency and merely exhibits the right-hand half. Some other particle sensors using solid-state lasers (SSL), however, prefer to employ a pair of acousto-optic modulators (AOM) as frequency shifters, which pronouncedly increases the complexity and the cost of the whole system. In this paper, linear modulation current is applied to a LD to achieve laser frequency tuning and conveniently shift the concerned Lorentz peak to any desired spectrum position. Moreover, higher-order harmonics of the shifted Lorentz peak, arising from intrinsically tilted SMI fringes, exhibit wider spectrum broadening than the main peak and can be employed to improve the sensitivity in nano-particle recognition. The technique proposed has been validated by simulation and experimental results, and it is beneficial to developing low-cost, compact and highly sensitive SMI particle sensors or instruments.

Robust estimation of 1/f activity improves oscillatory burst detection.

Neural oscillations often occur as transient bursts with variable amplitude and frequency dynamics. Quantifying these effects is important for understanding brain-behaviour relationships, especially in continuous datasets. To robustly measure bursts, rhythmical periods of oscillatory activity must be separated from arrhythmical background 1/f activity, which is ubiquitous in electrophysiological recordings. The Better OSCillation (BOSC) framework achieves this by defining a power threshold above the estimated background 1/f activity, combined with a duration threshold. Here we introduce a modification to this approach called fBOSC, which uses a spectral parametrisation tool to accurately model background 1/f activity in neural data. fBOSC (which is openly available as a MATLAB toolbox) is robust to power spectra with oscillatory peaks and can also model non-linear spectra. Through a series of simulations, we show that fBOSC more accurately models the 1/f power spectrum compared with existing methods. fBOSC was especially beneficial where power spectra contained a 'knee' below ~.5-10 Hz, which is typical in neural data. We also found that, unlike other methods, fBOSC was unaffected by oscillatory peaks in the neural power spectrum. Moreover, by robustly modelling background 1/f activity, the sensitivity for detecting oscillatory bursts was standardised across frequencies (e.g., theta- and alpha-bands). Finally, using openly available resting state magnetoencephalography and intracranial electrophysiology datasets, we demonstrate the application of fBOSC for oscillatory burst detection in the theta-band. These simulations and empirical analyses highlight the value of fBOSC in detecting oscillatory bursts, including in datasets that are long and continuous with no distinct experimental trials.

The hand tremor spectrum is modified by the inertial sensor mass during lightweight wearable and smartphone-based assessment in healthy young subjects

Tremors are common disorders characterized by an involuntary and relatively rhythmic oscillation that can occur in any part of the body and may be physiological or associated with some pathological condition. It is known that the mass loading can change the power spectral distribution of the tremor. Nowadays, many instruments have been used in the evaluation of tremors with bult-in inertial sensors, such as smartphones and wearables, which can significantly differ in the device mass. The aim of this study was to compare the quantification of hand tremor using Fourier spectral techniques obtained from readings of accelerometers built-in a lightweight handheld device and a commercial smartphone in healthy young subjects. We recruited 28 healthy right-handed subjects with ages ranging from 18 to 40 years. We tested hand tremors at rest and postural conditions using lightweight wearable device (5.7 g) and smartphone (169 g). Comparing both devices at resting tremor, we found with smartphone the power distribution of peak ranging 5 and 12 Hz in both hands. With wearable, the result was similar but less evident. When comparing both devices in postural tremor, there were significant differences in both frequency ranges in peak frequency and peak amplitude in both hands. Our main findings show that in resting condition the hand tremor spectrum had a higher peak amplitude in the 5–12 Hz range when the tremor was recorded with smartphones, and in postural condition there was a significantly (p < 0.05) higher peak power spectrum and peak frequency in the dominant hand tremors recorded with smartphones compared to those obtained with lightweight wearable device. Devices having different masses can alter the features of the hand tremor spectrum and their mutual comparisons can be prejudiced.

Low-Complexity Frequency Offset Estimation for Probabilistically Shaped MQAM Coherent Optical Systems

Since the reduction of the proportion of high modulus constellation points with π/4 + <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> π/2 ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> = 0, 1, 2, 3) modulation phase in probabilistically shaped (PS)- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary quadrature amplitude modulation (MQAM) deteriorates the power spectrum peak of frequency offset from the 4th power signal, the conventional 4th power Fast Fourier Transform (FFT) algorithm is not suitable for PS-MQAM under moderate or strong shaping. In this paper a low-complexity multi-format frequency offset estimation (FOE) scheme is proposed, where the coarse estimation is based on extended quadrature phase shift keying (QPSK) partitioning and quasi-linear approximation in polar coordinates at the first stage, and the fine estimation in subsequent stage using Digital Amplification and 4th power FFT with Sparse Operation. The computational complexity is approximately reduced by 71% compared with radius directed (RD) 4th power FFT algorithm with the same mutual information (MI) performance under 2e-2 bit error rate (BER). Dual polarization (DP) PS-16/32/64QAM numerical simulations prove that the normalized mean square error (NMSE) of proposed FOE scheme is an order of magnitude lower than that of RD 4th power FFT algorithm. The higher FOE accuracy has been demonstrated experimentally in DP PS-16/32QAM systems.

Performance of Ultra-High-Resolution Computed Tomography in Super High-Resolution Mode at the Routine Radiation Dose: Phantom Study.

Using a chest phantom, we compared the image quality of ultra-high-resolution computed tomography (U-HRCT) images acquired in super high-resolution (SHR) and normal resolution (NR) mode and at the routine radiation dose. The detector size was 0.25 and 0.5 mm, respectively. A chest phantom was scanned on a U-HRCT scanner. The scan parameters were tube voltage 120 kV and volume CT dose index 13.0 mGy, the routine radiation dose for conventional scans. The rotation time was 0.5 s/rot, the number of matrices was 512 in NR and 1024 in SHR mode. For physical evaluation, the modulation transfer function was measured on the spherical simulated nodule, and the noise power spectrum on the cylindrical water phantom. A CT value profile curve was created using an in-house simulated bronchial phantom. For visual evaluation, 3 radiologists and 3 radiology technologists evaluated overall image quality using a 4-grade scale (grade 1, poor; and grade 4, excellent). The 10% of modulation transfer function was 13.5 lp/cm in NR and 14.9 lp/cm in SHR mode ( P <0.01). ƒ peak was 5.6 lp/cm in NR and 8.8 lp/cm in SHR mode ( P <0.01), and the peak of noise power spectrum shifted. On the profile curves, the CT value at the edge changed in NR but not in SHR mode. The overall image quality was grade 3.0 ± 0.7 in SHR and grade 2.0 ± 0.7 in NR mode ( P <0.01). The image quality of SHR mode with U-HRCT was superior to that of NR mode at the routine radiation dose.

Analogue cosmological particle creation in an ultracold quantum fluid of light

The rapid expansion of the early universe resulted in the spontaneous production of cosmological particles from vacuum fluctuations, some of which are observable today in the cosmic microwave background anisotropy. The analogue of cosmological particle creation in a quantum fluid was proposed, but the quantum, spontaneous effect due to vacuum fluctuations has not yet been observed. Here we report the spontaneous creation of analogue cosmological particles in the laboratory, using a quenched 3-dimensional quantum fluid of light. We observe acoustic peaks in the density power spectrum, in close quantitative agreement with the quantum-field theoretical prediction. We find that the long-wavelength particles provide a window to early times. This work introduces the quantum fluid of light, as cold as an atomic Bose-Einstein condensate.