arXiv subjects

M. G. Kozlov

Publications and source records attributed to M. G. Kozlov.

At least 73 records · Page 4Linked to original sources

arXiv2013

Enhanced effects of temporal variation of the fundamental constants in ^{2}Π_{1/2} term diatomic molecules: ^{207}Pb^{19}F

The ^{207}Pb^{19}F molecule possesses a pair of closely spaced levels of opposite parity due to near cancelation of the omega-type doubling and magnetic hyperfine interaction energy shifts [Alphei et al., Phys. Rev. A, 83, 040501 (2011)]. We calculate the dependence of the transition frequency between these levels on the fine-structure constant (α) and the ratio of the light quark masses to the quantum chromodynamics scale (m_q/Λ_{QCD}), and find large enhancement of the relative effects of the variation of these parameters. Note that the effect of α-variation appears mainly due to the significant difference in the relativistic correction factors for the fine and hyperfine structure. We hence suggest the ^{207}Pb^{19}F molecule as a candidate system for investigating the possible temporal variation of the fundamental constants.

physics.atom-ph↗

arXiv2013

A search for varying fundamental constants using Hz-level frequency measurements of cold CH molecules

Many modern theories predict that the fundamental constants depend on time, position, or the local density of matter. We develop a spectroscopic method for pulsed beams of cold molecules, and use it to measure the frequencies of microwave transitions in CH with accuracy down to 3 Hz. By comparing these frequencies with those measured from sources of CH in the Milky Way, we test the hypothesis that fundamental constants may differ between the high and low density environments of the Earth and the interstellar medium. For the fine structure constant we find Δα/α= (0.3 +/- 1.1)*10^{-7}, the strongest limit to date on such a variation of α. For the electron-to-proton mass ratio we find Δμ/μ= (-0.7 +/- 2.2) * 10^{-7}. We suggest how dedicated astrophysical measurements can improve these constraints further and can also constrain temporal variation of the constants.

physics.atom-ph↗

arXiv2013

Microwave and submillimeter molecular transitions and their dependence on fundamental constants

Microwave and submillimeter molecular transition frequencies between nearly degenerated rotational levels, tunneling transitions, and mixed tunneling-rotational transitions show an extremely high sensitivity to the values of the fine-structure constant, alpha, and the electron-to-proton mass ratio, mu. This review summarizes the theoretical background on quantum-mechanical calculations of the sensitivity coefficients of such transitions to tiny changes in alpha and mu for a number of molecules which are usually observed in Galactic and extragalactic sources, and discusses the possibility of testing the space- and time-invariance of fundamental constants through comparison between precise laboratory measurements of the molecular rest frequencies and their astronomical counterparts. In particular, diatomic radicals CH, OH, NH+, and a linear polyatomic radical C3H in Pi electronic ground state, polyatomic molecules NH3, ND3, NH2D, NHD2, H2O2, H3O+, CH3OH, and CH3NH2 in their tunneling and tunneling-rotational modes are considered. It is shown that sensitivity coefficients strongly depend on the quantum numbers of the corresponding transitions. This can be used for astrophysical tests of Einstein's Equivalence Principle all over the Universe at an unprecedented level of sensitivity of ~10^-9, which is a limit three to two orders of magnitude lower as compared to the current constraints on cosmological variations of alpha and mu: Delta alpha/alpha < 10^-6, Delta mu/mu < 10^-7.

physics.atom-ph↗

arXiv2013

Exchange assisted tunneling and positron annihilation on inner atomic shells

It is known for a long time that the long range asymptotic behavior of the Hartree-Fock orbitals is different from that of the orbitals in the local potential. However, there is no consensus about observable physical effects associated with this asymptotics. Here we argue that weaker decrease of the Hartree-Fock orbitals at large distances is responsible for the positron annihilation on the inner shell electrons, which is observed experimentally.

physics.atom-ph↗

arXiv2013

Linear polyatomic molecules with Π ground state: sensitivity to variation of the fundamental constants

In polyatomic molecules with Π electronic ground state the ro-vibrational spectrum can be strongly modified by the Renner-Teller effect. The linear form of C3H molecule has particularly strong Renner-Teller interaction and a very low lying vibronic Σ+ level, which corresponds to the excited bending vibrational mode. This leads to the increased sensitivities of the microwave and submillimeter transition frequencies to the possible variation of the fine structure constant alpha and electron to proton mass ratio mu.

physics.atom-ph↗

arXiv2012

Blackbody radiation shift in the Sr optical atomic clock

We evaluated the static and dynamic polarizabilities of the 5s^2 ^1S_0 and 5s5p ^3P_0^o states of Sr using the high-precision relativistic configuration interaction + all-order method. Our calculation explains the discrepancy between the recent experimental 5s^2 ^1S_0 - 5s5p ^3P_0^o dc Stark shift measurement Δα= 247.374(7) a.u. [Middelmann et. al, arXiv:1208.2848 (2012)] and the earlier theoretical result of 261(4) a.u. [Porsev and Derevianko, Phys. Rev. A 74, 020502R (2006)]. Our present value of 247.5 a.u. is in excellent agreement with the experimental result. We also evaluated the dynamic correction to the BBR shift with 1 % uncertainty; -0.1492(16) Hz. The dynamic correction to the BBR shift is unusually large in the case of Sr (7 %) and it enters significantly into the uncertainty budget of the Sr optical lattice clock. We suggest future experiments that could further reduce the present uncertainties.

physics.atom-ph↗

arXiv2012

Study of the correlation effects in Yb^+ and implications for parity violation

Calculation of the energies, magnetic dipole hyperfine structure constants, E1 transition amplitudes between the low-lying states, and nuclear spin-dependent parity-nonconserving amplitudes for the ^2S_{1/2} - ^2D_{3/2,5/2} transitions in ^{171}Yb^+ ion is performed using two different approaches. First, we carried out many-body perturbation theory calculation considering Yb^+ as a monovalent system. Additional all-order calculations are carried out for selected properties. Second, we carried out configuration interaction calculation considering Yb as a 15-electron system and compared the results obtained by two methods. The accuracy of different methods is evaluated. We find that the monovalent description is inadequate for evaluation of some atomic properties due to significant mixing of the one-particle and the hole-two-particle configurations. Performing the calculation by such different approaches allowed us to establish the importance of various correlation effects for Yb^+ atomic properties for future improvement of theoretical precision in this complicated system.

physics.atom-ph↗

arXiv2012

Polarizabilities of Si^{2+}: a benchmark test of theory and experiment

We have calculated electric-dipole polarizabilities of the 3s^2 ^1S_0, 3s3p ^3P_0, and 3s3p ^1P_1 states of the Si^{2+} ion using recently developed configuration interaction + all-order method. Detailed evaluation of the uncertainties of the final results is carried out. Our value for the ground state electric-dipole polarizability 11.670(13) a.u. is in excellent agreement with the resonant excitation Stark ionization spectroscopy value 11.669(9) a.u. [Komara et al., J. Phys. B 38, 87 (2005); Mitroy, Phys. Rev. A 78, 052515 (2008)]. This work represents the most precise benchmark test to date of theory and experiment in divalent atoms. The near cancellation of the ns^2 ^1S_0 ground state and the lowest nsnp ^3P_0 polarizabilities previously observed in B+, Al+, In+, Tl+, and Pb^{2+} is also found in Si^{2+} ion.

physics.atom-ph↗

arXiv2012

Study of quadrupole polarizabilities with combined configuration interaction and coupled-cluster method

The recently developed method combining the configuration interaction and the coupled-cluster method was demonstrated to provide accurate treatment of correlation corrections in divalent atomic systems [M.S.Safronova, M.G.Kozlov, and C.W.Clark, Phys. Rev. Lett. 107, 143006 (2011)]. We have extended this approach to the calculation of quadrupole polarizabilities alpha_2 and applied it to evaluate alpha_2 for the ground state of Mg and Mg-like Si^{2+}. Performing the calculations in three different approximations of increasing accuracy allowed us to place the upper bounds on the uncertainty of the final results. The recommended values alpha_2(3s^2 1S0)= 35.86(13) a.u. for Si^{2+} and alpha_2(3s^2 1S0)= 814(3) a.u. for Mg are estimated to be accurate to 0.37%. Differences in quadrupole polarizability contributions in neutral Mg and Si^{2+} ion are discussed.

physics.atom-ph↗

arXiv2012

An upper limit to the variation in the fundamental constants at redshift z = 5.2

Aims. We constrain a hypothetical variation in the fundamental physical constants over the course of cosmic time. Methods. We use unique observations of the CO(7-6) rotational line and the [CI] 3P_2 - 3P_1 fine-structure line towards a lensed galaxy at redshift z = 5.2 to constrain temporal variations in the constant F = alpha^2/mu, where mu is the electron-to-proton mass ratio and alpha is the fine-structure constant. The relative change in F between z = 0 and z = 5.2, dFF = (F_obs - F_lab)/F_lab, is estimated from the radial velocity offset, dV = V_rot - V_fs, between the rotational transitions in carbon monoxide and the fine-structure transition in atomic carbon. Results. We find a conservative value dV = 1 +/- 5 km/s (1sigma C.L.), which when interpreted in terms of dFF gives dFF < 2x10^-5. Independent methods restrict the mu-variations at the level of dmm < 1x10^-7 at z = 0.7 (look-back time t_z0.7 = 6.4 Gyr). Assuming that temporal variations in mu, if any, are linear, this leads to an upper limit on dmm < 2x10^-7 at z = 5.2 (t_z5.2 = 12.9 Gyr). From both constraints on dFF and dmm, one obtains for the relative change in alpha the estimate daa < 8x10^-6, which is at present the tightest limit on daa at early cosmological epochs.

astro-ph.CO↗

arXiv2012

Anomalously small blackbody radiation shift in Tl+ frequency standard

The operation of atomic clocks is generally carried out at room temperature, whereas the definition of the second refers to the clock transition in an atom at absolute zero. This implies that the clock transition frequency should be corrected in practice for the effect of finite temperature of which the leading contributor is the blackbody radiation (BBR) shift. In the present work, we used configuration interaction + coupled-cluster method to evaluate polarizabilities of the $6s^2 ^1S_0$ and $6s6p ^3P_0$ states of Tl$^+$ ion; we find $α_0(^1S_0)=19.6$ a.u. and $α_0(^3P_0)=21.4$ a.u.. The resulting BBR shift of the $6s6p ^3P_0 - 6s^2 ^1S_0$ Tl$^+$ transition at $300 K$ is $Δν_{\rm BBR}=-0.0157(16)$ Hz. This result demonstrates that near cancelation of the $^1S_0$ and $^3P_0$ state polarizabilities in divalent B+, Al+, In$^+$ ions of group IIIB [Safronova \textit{et al.}, PRL 107, 143006 (2011)] continues for much heavier Tl$^+$, leading to anomalously small BBR shift for this system. This calculation demonstrates that the BBR contribution to the fractional frequency uncertainty of the Tl+ frequency standard at 300K is $1\times10^{-18}$. We find that Tl+ has the smallest fractional BBR shift among all present or proposed frequency standards with the exception of Al+.

physics.atom-ph↗

arXiv2012

Electric dipole moment enhancement factor of thallium

The goal of this work is to resolve the present controversy in the value of the EDM enhancement factor of Tl. We have carried out several calculations by different high-precision methods, studied previously omitted corrections, as well as tested our methodology on other parity conserving quantities. We find the EDM enhancement factor of Tl to be equal to -573(20). This value is 20% larger than the recently published result of Nataraj et al. [Phys. Rev. Lett. 106, 200403 (2011)], but agrees very well with several earlier results.

physics.atom-ph↗

arXiv2011

Precision calculation of blackbody radiation shifts for optical frequency metrology

We show that three group IIIB divalent ions, B+, Al+, and In+, have anomalously small blackbody radiation (BBR) shifts of the ns^2 1S0 - nsnp 3P0 clock transitions. The fractional BBR shifts for these ions are at least 10 times smaller than those of any other present or proposed optical frequency standards at the same temperature, and are less than 0.3% of the Sr clock shift. We have developed a hybrid configuration interaction + coupled-cluster method that provides accurate treatment of correlation corrections in such ions, considers all relevant states in the same systematic way, and yields a rigorous upper bound on the uncertainty of the final results. We reduce the BBR contribution to the fractional frequency uncertainty of the Al+ clock to 4 \times 10^{-19} at T=300K. We also reduce the uncertainties due to this effect at room temperature to 10^{-18} level for B+ and In+ to facilitate further development of these systems for metrology and quantum sensing. These uncertainties approach recent estimates of the feasible precision of currently proposed optical atomic clocks.

physics.atom-ph↗

arXiv2011

Sensitivity of microwave transition in H2O2 to variation of the electron-to-proton mass ratio

Recent observation of several microwave transitions in H2O2 from the interstellar medium [Astron. Astrophys., 531, L8 (2011)] raised interest to this molecule as yet another sensitive probe of the tentative variation of the electron-to-proton mass ratio mu. We estimate sensitivity coefficients of the microwave transitions in H2O2 to mu-variation. The largest coefficient for 14.8 GHz transition is equal to 37, which is comparable to highest sensitivities in methanol and an order of magnitude higher than sensitivity of the tunneling transition in ammonia.

astro-ph.CO↗

arXiv2011

Methanol as a tracer of fundamental constants

The methanol molecule CH3OH has a complex microwave spectrum with a large number of very strong lines. This spectrum includes purely rotational transitions as well as transitions with contributions of the internal degree of freedom associated with the hindered rotation of the OH group. The latter takes place due to the tunneling of hydrogen through the potential barriers between three equivalent potential minima. Such transitions are highly sensitive to changes in the electron-to-proton mass ratio, mu = m_e/m_p, and have different responses to mu-variations. The highest sensitivity is found for the mixed rotation-tunneling transitions at low frequencies. Observing methanol lines provides more stringent limits on the hypothetical variation of mu than ammonia observation with the same velocity resolution. We show that the best quality radio astronomical data on methanol maser lines constrain the variability of mu in the Milky Way at the level of |Delta mu/mu| < 28x10^{-9} (1sigma) which is in line with the previously obtained ammonia result, |Delta mu/mu| < 29x10^{-9} (1σ). This estimate can be further improved if the rest frequencies of the CH3OH microwave lines will be measured more accurately.

astro-ph.CO↗

arXiv2011

Sensitivity of the isotopologues of hydronium to variation of the electron-to-proton mass ratio

We study the sensitivity of the microwave and submillimeter transitions of the isotopologues of hydronium to the variation of the electron-to-proton mass ratio mu. These sensitivities are enhanced for the low frequency mixed inversion-rotational transitions. The lowest frequency transition (6.6 GHz) takes place for isotopologue H2DO+ and respective sensitivity to mu-variation is close to 200. This is about two orders of magnitude larger than the sensitivity of the inversion transition in ammonia, which is currently used for the search of mu-variation in astrophysics.

physics.atom-ph↗

arXiv2011

Rotational spectrum of molecular ion NH^+ as a probe for alpha- and m_e/m_p-variation

We identify the molecular ion NH^+ as a potential candidate for probing variations in the fine structure constant alpha and electron-to-proton mass ratio mu. NH^+ has an anomalously low-lying excited Sigma state, being only a few hundred cm^-1 above the ground Pi state. Being a light molecule, this proximity is such that rotational levels of the respective states are highly intermixed for low angular momenta. We find that several low-frequency transitions within the collective rotational spectrum experience enhanced sensitivity to alpha- and mu-variation. This is attributable to the close proximity of the Pi and Sigma states, as well as the ensuing strong spin-orbit coupling between them. Suggestions that NH^+ may exist in interstellar space and recent predictions that trapped-ion precision spectroscopy will be adaptable to molecular ions make NH^+ a promising system for future astrophysical and laboratory studies of alpha- and mu-variation.

physics.atom-ph↗

arXiv2010

Searching for Chameleon-like Scalar Fields

Using the 32-m Medicina, 45-m Nobeyama, and 100-m Effelsberg telescopes we found a statistically significant velocity offset Delta V = 27 +/- 3 m/s (1sigma) between the inversion transition in NH3(1,1) and low-J rotational transitions in N2H+(1-0) and HC3N(2-1) arising in cold and dense molecular cores in the Milky Way. Systematic shifts of the line centers caused by turbulent motions and velocity gradients, possible non-thermal hyperfine structure populations, pressure and optical depth effects are shown to be lower than or about 1 m/s and thus can be neglected in the total error budget. The reproducibility of Delta V at the same facility (Effelsberg telescope) on a year-to-year basis is found to be very good. Since the frequencies of the inversion and rotational transitions have different sensitivities to variations in mu = m_e/m_p, the revealed non-zero Delta V may imply that mu changes when measured at high (terrestrial) and low (interstellar) matter densities as predicted by chameleon-like scalar field models - candidates to the dark energy carrier. Thus we are testing whether scalar field models have chameleon-type interactions with ordinary matter. The measured velocity offset corresponds to the ratio Delta mu/mu = (mu_space - mu_lab)/mu_lab of (26 +/- 3)x10^{-9} (1sigma).

astro-ph.CO↗