Periodic Spectral Modulations Research Articles

Ultrafast Modulations in Stellar, Solar and Galactic Spectra: Dark Matter and Numerical Ghosts, Stellar Flares and SETI

Background: - From new results presented in the literature we discuss the hypothesis, presented in an our previous work, that the ultrafast periodic spectral modulations at fS=0.607±0.08 THz found in the spectra of 236 stars of the Sloan Digital Sky Survey (SDSS) were due to oscillations induced by dark matter (DM) cores in their centers that behave as oscillating boson stars. Two other frequencies were found by Borra in the redshift-corrected SDSS galactic spectra, f1,G=9.71−0.19+0.20 THz and f2,G=9.17−0.16+0.18 THz; the latter was then shown by Hippke to be a spurious frequency introduced by the data analysis procedure. Results: - Within the experimental errors, the frequency f1,G is the beating of the two frequencies, the spurious one, f2,G and fS that was also independently detected in a real solar spectrum, but not in the Kurucz’s artificial solar spectrum by Hippke, suggesting that fS could actually be a real frequency. Independent SETI observations by Isaacson et al., taken at different epochs, of four of these 236 stars could not confirm with high confidence - without completely excluding - the presence of fS in their power spectra and with the same power initially observed. Instead, the radio SETI deep-learning analysis with artificial intelligence (AI) gave an indirect confirmation of the presence of fS through the detection of a narrowband Doppler drifting of the observed radio signals in two stars, over a sample of 7 with a high S/N. These two stars belong to the set of the 236 SDSS stars. Numerical simulations confirm that this drifting can be due to frequency and phase modulation in time of the observed frequencies (1.3–1.7 GHz) with fS. Conclusions: - Assuming the DM hypothesis, the upper mass limit of the axion-like DM particle is ma≃2.4×103μeV, in agreement with the results from the gamma ray burst GRB221009A, laser interferometry experiments, suggesting new physics with additional axion-like particle fields for the muon g-2 anomaly.

The Breakthrough Listen Search for Intelligent Life: No Evidence of Claimed Periodic Spectral Modulations in High-resolution Optical Spectra of Nearby Stars

We report on high-resolution spectra obtained by the Automated Planet Finder and high-resolution optical Levy Spectrometer to search for periodic spectral modulations, such as those reported in Borra & Trottier. In their analysis of 2.5 million spectra from the Sloan Digital Sky Survey, Borra & Trottier report periodic spectral modulations in 234 stars, and suggest that these signals may be evidence of extraterrestrial civilizations. To evaluate this claim, we observed three of the 234 stars with the Automated Planet Finder Telescope and Levy Spectrometer including all stars brighter than a visual magnitude of 14. Fourier analysis of the resultant spectra of these three sources does not reveal any periodic spectral modulations at the reported period, nor at any other period.

Periodic spectral modulations of low-energy, low-charge-state carbon ions accelerated in an intense laser–solid interaction

We report experimental observation of periodic modulations in the energy distribution of C1+ ions dominantly accelerated in the interaction of a 15 μm thick tape target with intense laser pulses of intensities ∼1018 W/cm2 in a defocused configuration. Moreover, the influence of laser intensity on the acceleration of low- and high-charge-state species of carbon ions is observed. Two-dimensional (2D) particle-in-cell simulations elucidate the dynamics of ionization-dependent acceleration of different species in different laser focusing conditions. By comparison, 1D simulations suggest that the modulations of C1+ ions are due to the longitudinal recirculation dynamics of hot electrons in the target, which modulates the sheath field for acceleration of C1+ ions.

Coexistence of bound soliton and harmonic mode-locking soliton in an ultrafast fiber laser based on MoS2-deposited microfiber photonic device

As the typical material of two-dimensional transition metal dichalcogenides (TMDs), few-layered MoS2 possesses broadband saturable absorption and a large nonlinear refractive index, which could be regarded as a promising candidate for dual-function photonic device fabrication. In this work, the coexistence of a bound soliton and harmonic mode-locking soliton was demonstrated in an ultrafast fiber laser based on a MoS2-deposited microfiber photonic device. Through a band-pass filter, each multi-soliton state was investigated separately. The bound soliton has periodic spectral modulation of 1.55 nm with a corresponding pulse separation of 5.16 ps. The harmonic mode-locking soliton has the repetition rate of 479 MHz, corresponding to the 65th harmonic of the fundamental repetition rate. The results indicated that there exist more possibilities of different multi-soliton composites, which would enhance our understanding of multi-soliton dynamics.

Free Carrier Emergence and Onset of Electron-Phonon Coupling in Methylammonium Lead Halide Perovskite Films.

Sub-10 fs resolution pump-probe experiments on methylammonium lead halide perovskite films are described. Initial response to photoexcitation is assigned to localized hot excitons which dissociate to free carriers. This is attested to by band integrals of the pump-probe spectra where photoinduced bleaching rises abruptly 20 fs after photoexcitation. Later stages of spectral evolution are consistent with hot carrier cooling, during which state filling induced bleaching of interband and exciton transitions curiously more than doubles. Electron coupling to optical phonons is observed as periodic spectral modulations in the pump-probe data of both films. Fourier analysis identifies active phonons at ∼100 and 300 wavenumbers pertaining to the lead-halide framework and organic cation motions, respectively. Coupling strengths estimated from the depth of these modulations are in the weak coupling limit, in agreement with values extracted from temperature dependent emission line shape analysis. These findings support free carriers in these materials existing as large polarons. Accordingly, these modes are probably not dictating the moderate carrier mobility in this material.

Oscillating Stars and the Evidence of Dark Matter. A Comment on “Can the Periodic Spectral Modulations Observed in 236 Sloan Sky Survey Stars Be Due To Dark Matter Effects?” by F. Tamburini and I. Licata

Dark matter is probably the most fascinating enigma of modern physics. Its evidence is onall the astrophysical scales, from the local ones, inside our galaxy, to the outer galaxies, to themasses of galaxies, to the cosmological scales [1,2]. If we consider the standard cosmological model,based on general relativity and observed families of elemental particles, dark matter is inevitable:it needs to explain the formation and stability of all observed cosmic structures. Likewise, a series ofobservations based on the brightness distance of Type Ia supernovae, the cosmic background radiation,the distribution of cosmic structures, the so-called baryonic acoustic oscillations, and other observables,clearly indicate that cosmological fluid is experiencing an accelerate expansion. The cause of this factis generally attributed to the cosmological constant or to an undefined form of dark energy that wouldaccelerate the Universe [3].Despite these macroscopic evidences, despite the fact that general relativity always receives newconfirmations (the recent discovery of gravitational waves is one of the most striking recent examples),the fundamental constituents of dark matter and obscure energy appear extremely elusive. All directand indirect research of particle with mass interacting gravitationally but not electromagnetically seemto be unsuccessful today. From a general point of view, the Standard Model of elemental particlesseems to be extremely solid without leaving room for other exotic particles. On the other hand,even modifying the so-called gravitational sector can be problematic if the alternate theories of generalrelativity do not reproduce the results of the latter, which are experimentally well-founded, at least atlocal scales [4].In this complex research framework, a recent work on the prestigious research journalPhysica Scripta, Fabrizio Tamburini of ZKM in Karlsruhe and MSC-BW in Stuttgart and IgnazioLicata of ISEM in Palermo, could represent a totally original turning point in the research landscape ofcandidates for dark matter [5].The two researchers started from the recent data reported for main sequence stars under theSloan Digital Sky Survey collaboration. For 236 of these stars, Borra and Trottier [6] exhibitedan extremely regular periodic modulation in the spectrum. Signals appear so regular that they evensuggest an intelligent source of them within the SETI program that seeks extraterrestrial civilizations.Tamburini and Licata, on the other hand, considering the theoretical characteristics of weak interactingmassive particles (WIMPs) and axions (among the major candidates for dark matter), indicate inthis modulation as clear evidence for axions. In particular, Tamburini and Licata, starting from thefrequencies observed, have established a plausible range for the mass of the axion that overlaps withthe range obtained recently from Borsanyi et al. from Lattice QCD calculations including StandardModel particles [7]. In other words, the frequency modulation observed in these 236 stars would bedue to oscillations of axions. These particles could be clustered into astrophysical structures insidestars or form the so-called ‘boson stars’ and, above all, the particles would be compatible with the

Can the periodic spectral modulations observed in 236 Sloan Sky Survey stars be due to dark matter effects?

The search for dark matter (DM) is one of the most active and challenging areas of current research. Possible DM candidates are ultralight fields such as axions and weak interacting massive particles (WIMPs). Axions piled up in the center of stars are supposed to generate matter/DM configurations with oscillating geometries at a very rapid frequency, which is a multiple of the axion mass mB (Brito et al (2015); Brito et al (2016)). Borra and Trottier (2016) recently found peculiar ultrafast periodic spectral modulations in 236 main sequence stars in the sample of 2.5 million spectra of galactic halo stars of the Sloan Digital Sky Survey (∼1% of main sequence stars in the F–K spectral range) that were interpreted as optical signals from extraterrestrial civilizations, suggesting them as possible candidates for the search for extraterrestrial intelligence (SETI) program. We argue, instead, that this could be the first indirect evidence of bosonic axion-like DM fields inside main sequence stars, with a stable radiative nucleus, where a stable DM core can be hosted. These oscillations were not observed in earlier stellar spectral classes probably because of the impossibility of starting a stable oscillatory regime due to the presence of chaotic motions in their convective nuclei. The axion mass values, , obtained from the frequency range observed by Borra and Trottier, ) THz, agree with the recent theoretical results from high-temperature lattice quantum chromodynamics (Borsanyi et al (2016); Borsanyi et al (2016b)).

Discovery of Peculiar Periodic Spectral Modulations in a Small Fraction of Solar-type Stars

A Fourier transform analysis of 2.5 million spectra in the Sloan Digital Sky Survey was carried out to detect periodic spectral modulations. Signals having the same period were found in only 234 stars overwhelmingly in the F2 to K1 spectral range. The signals cannot be caused by instrumental or data analysis effects because they are present in only a very small fraction of stars within a narrow spectral range and because signal-to-noise ratio considerations predict that the signal should mostly be detected in the brightest objects, while this is not the case. We consider several possibilities, such as rotational transitions in molecules, rapid pulsations, Fourier transform of spectral lines, and signals generated by extraterrestrial intelligence (ETI). They cannot be generated by molecules or rapid pulsations. It is highly unlikely that they come from the Fourier transform of spectral lines because too many strong lines located at nearly periodic frequencies are needed. Finally, we consider the possibility, predicted in a previous published paper, that the signals are caused by light pulses generated by ETI to makes us aware of their existence. We find that the detected signals have exactly the shape of an ETI signal predicted in the previous publication and are therefore in agreement with this hypothesis. The fact that they are only found in a very small fraction of stars within a narrow spectral range centered near the spectral type of the Sun is also in agreement with the ETI hypothesis. However, at this stage, this hypothesis needs to be confirmed with further work. Although unlikely, there is also a possibility that the signals are due to highly peculiar chemical compositions in a small fraction of galactic halo stars.

Bragg reflection waveguide twin-beam lasers

We report on an edge-emitting diode laser with an ultra-narrow twin-lobed far field based on a dual-sided Bragg reflection waveguide. Lasers with a stripe width of 10 μm exhibit two stable near-circular beams symmetrically located at about ±31° with full width at half maximum (FWHM) of 7.2° and 5.4° respectively in the vertical and lateral directions. The mechanism behind the achievement of the twin-beam output is presented, and the symmetry of these two beams is analyzed by comparing the beam FWHM and power distribution. Single longitudinal mode operation is achieved and periodic spectral modulation is observed.

Spectral superresolution with ultrashort optical pulses

A superresolution technique for the measurement of transmission, reflection, and absorption spectra is proposed. An ultrashort laser pulse is propagated in a dispersive element and then periodically phase modulated. The temporal modulation is transformed into periodic spectral modulation, for which the number of harmonics, 2M+1, is determined by the modulation index. The modulated pulse is transmitted through (reflected from) the sample to be tested and measured by a spectrometer. By performing 2M+1 measurements for 2M+1 delays between the dispersed pulse and modulation signal, one can restore the spectral response of the sample with superresolution after simple processing. We numerically demonstrate the measurement of the transmission spectrum of an ultranarrow optical filter with a minimum feature of 0.43 pm by an optical spectrum analyzer with a 10 pm resolution. A twentyfold enhancement of the resolution is achieved in the presence of noise with a level of 0.1%. The advantage of the system is its full reconfigurability.

Ground plane microphone for measurement of aircraft flyover noise

Ground interference distortion is present in aircraft flyover noise spectra acquired using microphones mounted on poles, such as the 1.2-m height required for noise certification. This spectral distortion is undesirable and can be avoided by using microphones that are mounted flush with the surface of a large, flat, acoustically hard surface. However, flush mounting is usually not possible. As a practical implementation of a flush installation, Boeing has developed the flush-dish microphone that consists of a dish placed on the ground with its convex side up. The microphone is flush mounted at the center of the dish. Two designs of this concept, circular and exponential flush-dish microphones, are described in this paper. The first design, the circular flush dish, was found to be free from ground interference effects for all incidence angles except for angles within about 15 deg of the overhead position. In this region, it exhibited periodic spectral modulation due to the interaction between direct and edge-diffracted waves. To diminish the edge effect, a new design, the exponential flush dish, was conceived. The edge was shaped to gradually match the impedance between the dish and the ground and to avoid the in-phase addition of edge-diffracted waves. The experimental results showed the exponential dish to be free from edge diffraction and ground interference effects. Furthermore, the response was insensitive to whether the flush dish was mounted on an acoustically hard surface or a typical natural terrain.