arXiv subjects

S. A. Levshakov

Publications and source records attributed to S. A. Levshakov.

At least 19 recordsLinked to original sources

arXiv2026

Constraints on mu-variations from the methanol CH3OH thermal lines in the Galaxy at galactocentric distances of 1.5 < D_GC < 13 kpc

In this study, constraints are set on hypothetical variations of the fundamental physical constant mu = m_e/m_p - the electron-to-proton mass ratio - based on thermal emission lines of E-methanol (CH3OH) in the 216-220 GHz frequency range. Molecular spectra toward seven massive clouds located across a wide range of galactocentric distances (1.5 < D_GC < 13 kpc) have been analyzed. The obtained weighted mean value = (0.5+/-0.5)*10^(-7) does not indicate statistically significant changes in mu at the 1 sigma confidence level of 5*10^(-8), which is in good agreement with previously established upper limits in a number of molecular clouds in the Galactic disk.

astro-ph.GA↗

arXiv2026

Indications of electron-to-proton mass ratio variations in the Galaxy. III. 0.6mm methanol lines toward SgrB2(N) and Orion-KL

In this paper, we show that methanol (CH3OH) torsional-rotational transitions, which have increased sensitivity to small variations of mu - the electron-to-proton mass ratio, are shifted relative to less sensitive transitions in the spectrum of the SgrB2(N) molecular cloud located at the Galactic center. At the same time, an identical set of methanol lines in the spectrum of the Orion-KL molecular cloud, located far from the center, shows no shifts. Interpreting this behavior of molecular frequencies in terms of Delta mu/mu = (mu_obs - mu_lab)/mu_lab leads to the following weighted mean values: = (-3.4 +/- 0.4)*10^(-7) for SgrB2 and = (-1.1 +/- 0.8)*10^(-7) for Orion-KL (indicated are the total +/-1sigma errors of the weighted means including both statistical and systematic uncertainties). A possible correlation between values measured in various molecular clouds of the Galactic disk and the distribution of dark matter along the Galactic radius is discussed, which may suggest a hypothetical modulation of the Higgs scalar field by dark matter, resulting in a change of mu.

astro-ph.GA↗

arXiv2025

Acetaldehyde as a molecule for testing variations of electron-to-proton mass ratio

We present the quantum-mechanical calculations of the dimensionless sensitivity coefficients Q to small changes in the fundamental physical constant mu = m_e/m_p - the electron-to-proton mass ratio - for a number of low-frequency (1-50 GHz) transitions of the acetaldehyde (CH3CHO) molecule. The calculations show that Q varies in the range from 0.62 to 3.61. An example of the practical use of the CH3CHO and CH3OH lines tracing the same regions in three molecular clouds, located at large galactocentric distances (D_GC ~ 8 kpc) is considered. This results in a limit on the mu variations of Delta mu/mu = (0.1 +/- 0.4)*10^(-7) which is in line with previously obtained most stringent upper limits on changes in mu based on other molecules and methods. The limit obtained restricts hypothetical violations of the Einstein principle of the local position invariance at the level of 4*10^(-8) in the Galactic disk at large galactocentric distances.

physics.atom-ph↗

arXiv2025

Indications of electron-to-proton mass ratio variations in the Galaxy. II. 3 mm methanol lines toward Sgr B2(N) and (M)

Differential measurements of the fundamental constant mu = m_e/m_p (the electron-to-proton mass ratio) for two sources near the Galactic Center - the Sgr B2(N) and B2(M) molecular clouds - suggest that mu is lower in these clouds than its laboratory value. Based on observations of methanol (CH3OH) emission lines in the 80-112 GHz range (data from the IRAM 30-m telescope), a weighted mean value (Delta mu/mu) = (mu_obs - mu_lab)/mu_lab = (-2.1 +/- 0.6)*10^(-7) (1 sigma) was obtained for Sgr B2(N) at the sample size n = 9. This value of (Delta mu/mu) has the same sign as the result of recent measurements of methanol lines in the higher frequency range of 542-543 GHz (data from the Herschel space telescope) for Sgr B2(N): (Delta mu/mu) = (-4.2 +/- 0.7)*10^(-7) (sample size n = 2).

astro-ph.GA↗

arXiv2025

Indication of the electron-to-proton mass ratio variation within the Galaxy

Near (~100 pc) and far (~8.7 kpc) relative to the Galactic center, the molecular clouds SgrB2(N) and Orion-KL exhibit different values of the fundamental physical constant mu=m_e/m_p - the electron-to-proton mass ratio. Measured frequency difference between the emission lines of methanol (CH3OH), - J_K_u - J_K_l = 6_3 - 5_2 A+ 542000.981 MHz, 6_3 - 5_2 A- 542081.936 MHz, and 8_0 - 7_-1 E 543076.194 MHz, - observed with the space observatory Herschel toward SgrB2(N) and Orion-KL corresponds to (Sgr-Ori): Delta mu/mu = (-3.7 +/- 0.5)*10^(-7) (1 sigma C.L.). At the same time, comparison of the same methanol lines in Orion-KL with laboratory frequencies shows no significant changes in mu (Ori-lab): Delta mu/mu = (-0.5 +/- 0. 6)*10^(-7), while a comparison between SgrB2(N) and laboratory lines indicates a lower value of mu near the Galactic center (Sgr-lab): Delta mu/mu = (-4.2 +/- 0.7)*10^(-7). The reduced value of mu in SgrB2(N) is not explained by known systematic effects and requires further investigation.

astro-ph.GA↗

arXiv2024

Hyperfine structure of the methanol molecule as traced by Class I methanol masers

We present results on simultaneous observations of Class~I methanol masers at 25, 36, and 44 GHz towards 22 Galactic targets carried out with the Effelsberg 100-m telescope. The study investigates relations between the hyperfine (HF) structure of the torsion-rotation transitions in CH3OH and maser activity. By analyzing the radial velocity shifts between different maser lines together with the patterns of the HF structure based on laboratory measurements and quantum-chemical calculations, we find that in any source only one specific HF transition forms the maser emission and that this transition changes from source to source. The physical conditions leading to this selective behavior are still unclear. Using accurate laboratory rest frequencies for the 25 GHz transitions, we have refined the centre frequencies for the HF multiplets at 36, 44, and 95 GHz: f_36 = (36169.2488 +/- 0.0002_stat +/- 0.0004_sys) MHz. f_44 = (44069.4176 +/- 0.0002_stat +/- 0.0004_sys) MHz, and f_95 = (95169.4414 +/- 0.0003_stat +/- 0.0004_sys) MHz. Comparison with previous observations of 44 GHz masers performed 6-10 years ago with a Korean 21-m KVN telescope towards the same targets confirms the kinematic stability of Class~I maser line profiles during this time interval and reveals a systematic radial velocity shift of 0.013 +/- 0.005 km/s between the two telescopes.

astro-ph.GA↗

arXiv2024

Spectroscopic Shifts in Deuterated Methanol Induced by Variation of me/mp

Numerical calculations of the sensitivity coefficients, Q_mu, of microwave molecular transitions in the ground torsion-rotation state of deuterated methanol (CH3OD, CD3OH, and CD3OD) to small variations in the fundamental physical constant mu = me/mp - the electron-to-proton mass ratio - are reported. Theoretical motivation for changes in mu comes from a variety of models beyond the Standard Model of particle physics which are invoked to explain the nature of dark matter and dark energy that dominate the Universe. The calculated values of Q_mu range from -300 to +73 and, thus, make deuterated methanol promising for searches for small space-time changes in mu. It is also shown that among the calculated sensitivity coefficients Q_mu using different Hamiltonians in the present and previous works, there are several pronounced outliers of unclear nature.

hep-ph↗

arXiv2024

Torsion-rotational transitions in methanol as a probe of fundamental physical constants -- electron and proton masses

We report on the using of torsion-rotational transitions in the CH3OH and (13)CH3OH molecules to evaluate possible variations of the physical constant mu=m_e/m_p - the electron-to-proton mass ratio - from spectral observations of emission lines detected in the microwave range towards the dense molecular cloud Orion-KL. An estimate of the upper limit on the relative changes in mu is obtained by two independent ways - with (13)CH3OH lines and with the combination of (13)CH3OH and CH3OH lines. The calculated upper limit Delta mu/mu < 1.1*10^{-8} (1 sigma) is in line with the most stringent constraints on the variability of fundamental physical constants established by other astrophysical methods.

astro-ph.GA↗

arXiv2023

Hyperfine structure of methanol lines at 25 GHz

High-dispersion (channel width 0.015 km s^-1) laboratory spectroscopy of the torsion-rotation lines J_2 - J_1 (J = 2 - 6) in the ground torsional state (vt = 0) of the E-type methanol demonstrates multicomponent hyperfine splitting patterns at 25 GHz. The observed patterns are compared with simulations of CH3OH emission lines based on ab initio quantum-mechanical models. A substantial disparity between the laboratory and simulated patterns is revealed. The observed morphology of the line shapes is not reproduced in the model profiles. The found inconsistency requires further refinement of the current quantum-mechanical models to fit the observed hyperfine splitting patterns at 25 GHz.

physics.atom-ph↗

arXiv2023

Methanol isotopologues as a probe for spatial and temporal variations of the electron-to-proton mass ratio

We present results on numerical calculations of the sensitivity coefficients, Qmu, of microwave molecular transitions in (13C)H3OH and CH3(18O)H to the hypothetical variation in the fundamental physical constant mu - the electron-to-proton mass ratio. The invariability of mu in time and space is one of the basic assumptions of the Standard Model of particle physics which can be tested at cosmological scales by means of astronomical observations in the Galaxy and external galaxies. Our calculations show that these two methanol isotopologues can be utilized for such tests since their microwave transitions from the frequency interval 1-100 GHz exhibit a large spread in Qmu values which span a range of -109 < Qmu < 78. We show that the thermal emission lines of (13C)H3OH observed in the star-forming region NGC6334I constrain the variability of mu at a level of 3x10^-8 (1σ), which is in line with the most stringent upper limits obtained previously from observations of methanol (CH3OH) and other molecules in the Galaxy.

astro-ph.GA↗

arXiv2021

Probing the electron-to-proton mass ratio gradient in the Milky Way with class I methanol masers

We estimate limits on non-universal coupling of hypothetical hidden fields to standard matter by evaluating the fractional changes in the electron-to-proton mass ratio, mu = m_e/m_p, based on observations of ClassI methanol masers distributed in the Milky Way disk over the range of the galactocentric distances 4 < R < 12 kpc. The velocity offsets DeltaV = V44 - V95 measured between the 44 and 95 GHz methanol lines provide, so far, one of the most stringent constraints on the spatial gradient k_mu = d(Delta mu/mu)/dR < 2x10^-9 kpc-1 and the upper limit on Delta mu/mu < 2x10^-8, where Delta mu/mu = (mu_obs-mu_lab)/mu_lab. We also find that the offsets DeltaV are clustered into two groups which are separated by 0.022 +/- 0.003 km/s (1sigma C.L.). The grouping is most probably due to the dominance of different hyperfine transitions in the 44 and 95 GHz methanol maser emission. Which transition becomes favored is determined by an alignment (polarization) of the nuclear spins of the four hydrogen atoms in the methanol molecule. This result confirms that there are preferred hyperfine transitions involved in the methanol maser action.

astro-ph.GA↗

arXiv2021

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde IV. The ALMA view of N113 and N159W in the LMC

We mapped the kinetic temperature structure of two massive star-forming regions, N113 and N159W, in the Large Magellanic Cloud (LMC). We have used $\sim$1\hbox{$\,.\!\!^{\prime\prime}$}6\,($\sim$0.4\,pc) resolution measurements of the para-H$_2$CO\,$J_{\rm K_ aK_c}$\,=\,3$_{03}$--2$_{02}$, 3$_{22}$--2$_{21}$, and 3$_{21}$--2$_{20}$ transitions near 218.5\,GHz to constrain RADEX non-LTE models of the physical conditions. The gas kinetic temperatures derived from the para-H$_2$CO line ratios 3$_{22}$--2$_{21}$/3$_{03}$--2$_{02}$ and 3$_{21}$--2$_{20}$/3$_{03}$--2$_{02}$ range from 28 to 105\,K in N113 and 29 to 68\,K in N159W. Distributions of the dense gas traced by para-H$_2$CO agree with those of the 1.3\,mm dust and \emph{Spitzer}\,8.0\,$μ$m emission, but do not significantly correlate with the H$α$ emission. The high kinetic temperatures ($T_{\rm kin}$\,$\gtrsim$\,50\,K) of the dense gas traced by para-H$_2$CO appear to be correlated with the embedded infrared sources inside the clouds and/or YSOs in the N113 and N159W regions. The lower temperatures ($T_{\rm kin}$\,$<$\,50\,K) are measured at the outskirts of the H$_2$CO-bearing distributions of both N113 and N159W. It seems that the kinetic temperatures of the dense gas traced by para-H$_2$CO are weakly affected by the external sources of the H$α$ emission. The non-thermal velocity dispersions of para-H$_2$CO are well correlated with the gas kinetic temperatures in the N113 region, implying that the higher kinetic temperature traced by para-H$_2$CO is related to turbulence on a $\sim$0.4\,pc scale. The dense gas heating appears to be dominated by internal star formation activity, radiation, and/or turbulence. It seems that the mechanism heating the dense gas of the star-forming regions in the LMC is consistent with that in Galactic massive star-forming regions located in the Galactic plane.

astro-ph.GA↗

arXiv2020

Fundamental physical constants at low and high redshifts

Spacetime variations of physical constants can be associated with the existence of Higgs-like scalar field(s) that couple non-universally to the baryonic matter. Recent results of astronomical spectral measurements of the fractional changes in the electron-to-proton mass ratio, mu = m_e/m_p, at low (z ~ 0) and high (z ~ 6.5) redshifts are discussed. It is shown that the distribution of the most accurate estimates of Delta mu/mu = (mu_obs - mu_lab)/mu_lab ranging between z = 0 and z ~ 1100 can be approximated by a power low Delta mu/mu = k_mu (1+z)^p, with k_mu = (1.7 +/- 0.3)x10^-8 and p = 1.99 +/- 0.03, implying a dynamical nature of the scalar field(s).

astro-ph.CO↗

arXiv2020

Constraints on the electron-to-proton mass ratio variation at the epoch of reionization

Far infrared fine-structure transitions of CI and CII and rotational transitions of CO are used to probe hypothetical variations of the electron-to-proton mass ratio mu = m_e/m_p at the epoch of reionization (z > 6). A constraint on Delta mu/mu = (mu_obs - mu_lab)/mu_lab = (0.7 +/- 1.2)x10^-5 (1sigma) obtained at = 6.31 is the most stringent up-to-date limit on the variation of mu at such high redshift. For all available estimates of Delta mu/mu ranging between z = 0 and z = 1100, - the epoch of recombination, - a regression curve Delta mu/mu = k_mu (1+z)^p, with k_mu = (1.6 +/- 0.3) x10^-8 and p = 2.00 +/- 0.03, is deduced. If confirmed, this would imply a dynamical nature of dark matter/dark energy.

astro-ph.CO↗

arXiv2019

36 GHz methanol lines from nearby galaxies: maser or quasi-thermal emission?

Methanol (CH3OH) is one of the most abundant interstellar molecules, offering a vast number of transitions to be studied, including many maser lines. While the strongest Galactic CH3OH lines, the so-called class II masers, show no indications for the presence of superluminous counterparts in external galaxies, the less luminous Galactic class I sources appear to be different. Here we report class I 36GHz CH3OH 4(-1) - 3(0) E line emission from the nearby galaxies Maffei2 and IC342, measured with the 100-m telescope at Effelsberg at three different epochs within a time span of about five weeks. The 36GHz methanol line of Maffei2 is the second most luminous among the sources detected with certainty outside the Local Group of galaxies. This is not matched by the moderate infrared luminosity of Maffei2. Higher resolution data are required to check whether this is related to its prominent bar and associated shocks. Upper limits for M82, NGC4388, NGC5728 and Arp220 are also presented. The previously reported detection of 36GHz maser emission in Arp220 is not confirmed. Non-detections are reported from the related class I 44GHz methanol transition towards Maffei2 and IC342, indicating that this line is not stronger than its 36GHz counterpart. In contrast to the previously detected 36GHz CH3OH emission in NGC253 and NGC4945, our 36GHz profiles towards Maffei2 and IC342 are similar to those of previously detected non-masing lines from other molecular species. However, by analogy to our Galactic center region, it may well be possible that the 36GHz methanol lines in Maffei~2 and IC~342 are composed of a large number of faint and narrow maser features that remain spatially unresolved. In view of this, a search for a weak broad 36GHz line component would also be desirable in NGC253 and NGC4945.

astro-ph.GA↗

arXiv2019

Testing the weak equivalence principle by differential measurements of fundamental constants in the Magellanic Clouds

Non-standard fields are assumed to be responsible for phenomena attributed to dark energy and dark matter. Being coupled to ordinary matter, these fields modify the masses and/or charges of the elementary particles, thereby violating the Weak Equivalence Principle. Thus, values of fundamental constants such as the proton-to-electron mass ratio, mu, and/or the fine structure constant, alpha, measured in different environment conditions can be used as probes for this coupling. Here we perform differential measurements of F = mu*alpha^2 to test a non-standard coupling in the Magellanic Clouds - dwarf galaxies where the overall mass budget is dominated by dark matter. The analysis is based on [CI] and CO lines observed with the Herschel Space Observatory. Since these lines have different sensitivities to changes in mu and alpha, the combined alpha and mu variations can be evaluated through the radial velocity offsets, Delta V, between the CO and [CI] lines. Averaging over nine positions in the Magellanic Clouds, we obtain = -0.02+/-0.07 km/s, leading to |Delta F/F| < 2*10^-7 (1sigma), where Delta F/F = (F_obs-F_lab)/F_lab}. However, for one position observed with five times higher spectral resolution we find Delta V = -0.05+/-0.02 km/s, resulting in Delta F/F = (-1.7+/-0.7)*10^-7. Whether this offset is due to changes in the fundamental constants, due to chemical segregation in the emitting gas or merely due to Doppler noise requires further investigations.

astro-ph.CO↗

arXiv2017

Testing the variability of the proton-to-electron mass ratio from observations of methanol in the dark cloud core L1498

The dependence of the proton-to-electron mass ratio, mu, on the local matter density was investigated using methanol emission in the dense dark cloud core L1498. Towards two different positions in L1498, five methanol transitions were detected and an extra line was tentatively detected at a lower confidence level in one of the positions. The observed centroid frequencies were then compared with their rest frame frequencies derived from least-squares fitting to a large data set. Systematic effects, as the underlying methanol hyperfine structure and the Doppler tracking of the telescope, were investigated and their effects were included in the total error budget. The comparison between the observations and the rest frame frequencies constrains potential mu variation at the level of Dmu/mu < 6 x 10^(-8), at a 3 sigma confidence level. For the dark cloud we determine a total CH3OH (A+E) beam averaged column density of 3-4 x 10^(12) cm(-2) (within roughly a factor of two), an E- to A-type methanol column density ratio of N(A-CH3OH)/N(E-CH3OH) = 1.00 +/- 0.15, a density of n(H2) = 3 x 10^5 cm^(-3) (again within a factor of two), and a kinetic temperature of Tkin = 6 +/- 1 K. In a kinetic model including the line intensities observed for the methanol lines, the n(H2) density is higher and the temperature is lower than that derived in previous studies based on different molecular species; the intensity of the 1_0 --> 1_-1 E line strength is not well reproduced.

astro-ph.CO↗

arXiv2017

[CI], [CII] and CO emission lines as a probe for alpha variations at low and high redshifts

The offsets between the radial velocities of the rotational transitions of carbon monoxide and the fine structure transitions of neutral and singly ionized carbon are used to test the hypothetical variation of the fine structure constant, alpha. From the analysis of the [CI] and [CII] fine structure lines and low J rotational lines of 12CO and 13CO, emitted by the dark cloud L1599B in the Milky Way disk, we find no evidence for fractional changes in alpha at the level of |$Δα/α$| < 3*10^-7. For the neighbour galaxy M33 a stringent limit on Delta alpha/alpha is set from observations of three HII zones in [CII] and CO emission lines: |$Δα/α$| < 4*10^-7. Five systems over the redshift interval z = 5.7-6.4, showing CO J=6-5, J=7-6 and [CII] emission, yield a limit on |$Δα/α$| < 1.3*10^-5. Thus, a combination of the [CI], [CII], and CO emission lines turns out to be a powerful tool for probing the stability of the fundamental physical constants over a wide range of redshifts not accessible to optical spectral measurements.

astro-ph.GA↗