Proton-to-electron Mass Ratio Research Articles

RECONNECTION AND ELECTRON TEMPERATURE ANISOTROPY IN SUB-PROTON SCALE PLASMA TURBULENCE

Turbulent behavior at sub-proton scales in magnetized plasmas is important for a full understanding of the energetics of astrophysical flows such as the solar wind. We study the formation of electron temperature anisotropy due to reconnection in the turbulent decay of sub-proton scale fluctuations using two dimensional, particle-in-cell (PIC) plasma simulations with realistic electron-proton mass ratio and a guide field out of the simulation plane. A fluctuation power spectrum with approximately power law form is created down to scales of order the electron gyroradius. In the dynamic magnetic field topology, which gradually relaxes in complexity, we identify the signatures of collisionless reconnection at sites of X-point field geometry. The reconnection sites are generally associated with regions of strong parallel electron temperature anisotropy. The evolving topology of magnetic field lines connected to a reconnection site allows spatial mixing of electrons accelerated at multiple, spatially separated reconnection regions. This leads to the formation of multi-peaked velocity distribution functions with a strong parallel temperature anisotropy. In a three-dimensional system, supporting the appropriate wave vectors, the multi-peaked distribution functions would be expected to be unstable to kinetic instabilities, contributing to dissipation. The proposed mechanism of anisotropy formation is also relevant to space and astrophysical systems where the evolution of the plasma is constrained by linear temperature anisotropy instability thresholds. The presence of reconnection sites leads to electron energy gain, nonlocal velocity space mixing and the formation of strong temperature anisotropy; this is evidence of an important role for reconnection in the dissipation of turbulent fluctuations.

ANALYSIS OF MOLECULAR HYDROGEN ABSORPTION TOWARD QSO B0642–5038 FOR A VARYING PROTON-TO-ELECTRON MASS RATIO

Rovibronic molecular hydrogen (H$_2$) transitions at redshift $z_{\rm abs} \simeq 2.659$ towards the background quasar B0642$-$5038 are examined for a possible cosmological variation in the proton-to-electron mass ratio, $\mu$. We utilise an archival spectrum from the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph with a signal-to-noise ratio of $\sim$35 per 2.5-km$\,$s$^{-1}$ pixel at the observed H$_2$ wavelengths (335--410 nm). Some 111 H$_2$ transitions in the Lyman and Werner bands have been identified in the damped Lyman $\alpha$ system for which a kinetic gas temperature of $\sim$84 K and a molecular fraction $\log f = -2.18\pm0.08$ is determined. The H$_2$ absorption lines are included in a comprehensive fitting method, which allows us to extract a constraint on a variation of the proton-electron mass ratio, $\Delta\mu/\mu$, from all transitions at once. We obtain $\Delta\mu/\mu = (17.1 \pm 4.5_{\rm stat} \pm3.7_{\rm sys})\times10^{-6}$. However, we find evidence that this measurement has been affected by wavelength miscalibration errors recently identified in UVES. A correction based on observations of objects with solar-like spectra gives a smaller $\Delta\mu/\mu$ value and contributes to a larger systematic uncertainty: $\Delta\mu/\mu = (12.7 \pm 4.5_{\rm stat} \pm4.2_{\rm sys})\times10^{-6}$.

Ion acoustic traveling waves

AbstractModels for traveling waves in multi-fluid plasmas give essential insight into fully nonlinear wave structures in plasmas, not readily available from either numerical simulations or from weakly nonlinear wave theories. We illustrate these ideas using one of the simplest models of an electron–proton multi-fluid plasma for the case where there is no magnetic field or a constant normal magnetic field present. We show that the traveling waves can be reduced to a single first-order differential equation governing the dynamics. We also show that the equations admit a multi-symplectic Hamiltonian formulation in which both the space and time variables can act as the evolution variable. An integral equation useful for calculating adiabatic, electrostatic solitary wave signatures for multi-fluid plasmas with arbitrary mass ratios is presented. The integral equation arises naturally from a fluid dynamics approach for a two fluid plasma, with a given mass ratio of the two species (e.g. the plasma could be an electron–proton or an electron–positron plasma). Besides its intrinsic interest, the integral equation solution provides a useful analytical test for numerical codes that include a proton–electron mass ratio as a fundamental constant, such as for particle in cell (PIC) codes. The integral equation is used to delineate the physical characteristics of ion acoustic traveling waves consisting of hot electron and cold proton fluids.

Progress in the accuracy of the fundamental physical constants: 2010 CODATA recommended values

Every four years, the CODATA Task Group on Fundamental Constants presents tables of recommended values of the fundamental physical constants. Recently, 2010 CODATA recommended values (Mohr P J, Taylor B N, and Newell D B “CODATA recommended values of the fundamental physical constants: 2010” Rev. Mod. Phys. 84 1527 (2012)), based on global data up to 31 December 2010, were published. In the present review, we briefly analyze the new recommended values, as well as new original data, on which the determination is based. To facilitate the consideration, the data are subdivided into several groups. New original theoretical and experimental results are discussed for each group separately. Special attention is paid to experimental and theoretical progress in the determination of the Rydberg constant , the electron–proton mass ratio , the fine-structure constant , the Planck constant , the Boltzmann constant , the Newtonian constant of gravitation , and the anomalous magnetic moment of the muon . In conclusion, the prospects of redefining units of the International System (SI) in terms of fundamental physical constants, which is currently under active discussion by the metrological community, are considered. The very possibility and efficiency of a practical realization of such a scenario with the redefinition directly depends on the status of the determination of the fundamental constants.

Matter non-conservation in the universe and dynamical dark energy

In an expanding universe, the vacuum energy density ρΛ is expected to be a dynamical quantity. In quantum field theory in curved spacetime, ρΛ should exhibit a slow evolution, determined by the expansion rate of the universe H. Recent measurements on the time variation of the fine-structure constant and of the proton–electron mass ratio suggest that the basic quantities of the standard model, such as the QCD scale parameter ΛQCD, may not be conserved in the course of the cosmological evolution. The masses of the nucleons mN and of the atomic nuclei would also be affected. Matter is not conserved in such a universe. These measurements can be interpreted as a leakage of matter into vacuum or vice versa. We point out that the amount of leakage necessary to explain the measured value of could be of the same order of magnitude as the observationally allowed value of , with a possible contribution from the dark matter particles. The dark energy in our universe could be the dynamical vacuum energy in interaction with ordinary baryonic matter as well as with dark matter.

COA−Xsystem for constraining cosmological drift of the proton-electron mass ratio

The $\textrm{A}^1\Pi-\textrm{X}^1\Sigma^+$ band system of carbon monoxide, which has been detected in six highly redshifted galaxies ($z=1.6-2.7$), is identified as a novel probe method to search for possible variations of the proton-electron mass ratio ($\mu$) on cosmological time scales. Laboratory wavelengths of the spectral lines of the A-X ($v$,0) bands for $v=0-9$ have been determined at an accuracy of $\Delta\lambda/\lambda=1.5 \times 10^{-7}$ through VUV Fourier-transform absorption spectroscopy, providing a comprehensive and accurate zero-redshift data set. For the (0,0) and (1,0) bands, two-photon Doppler-free laser spectroscopy has been applied at the $3 \times 10^{-8}$ accuracy level, verifying the absorption data. Sensitivity coefficients $K_{\mu}$ for a varying $\mu$ have been calculated for the CO A-X bands, so that an operational method results to search for $\mu$-variation.

CONSTRAINING FUNDAMENTAL CONSTANT EVOLUTION WITH H I AND OH LINES

We report deep Green Bank Telescope spectroscopy in the redshifted HI 21cm and OH 18cm lines from the $z = 0.765$ absorption system towards PMN J0134-0931. A comparison between the "satellite" OH 18cm line redshifts, or between the redshifts of the HI 21cm and "main" OH 18cm lines, is sensitive to changes in different combinations of three fundamental constants, the fine structure constant $\alpha$, the proton-electron mass ratio $\mu \equiv m_p/m_e$ and the proton g-factor $g_p$. We find that the satellite OH 18cm lines are not perfectly conjugate, with both different line shapes and stronger 1612 MHz absorption than 1720 MHz emission. This implies that the satellite lines of this absorber are not suitable to probe fundamental constant evolution. A comparison between the redshifts of the HI 21cm and OH 18cm lines, via a multi-Gaussian fit, yields the strong constraint $[\Delta F/F] = [-5.2 \pm 4.3] \times 10^{-6}$, where $F \equiv g_p [\mu \alpha^2]^{1.57}$ and the error budget includes contributions from both statistical and systematic errors. We thus find no evidence for a change in the constants between $z = 0.765$ and the present epoch. Incorporating the constraint $[\Delta \mu/\mu ] < 3.6 \times 10^{-7}$ from another absorber at a similar redshift and assuming that fractional changes in $g_p$ are much smaller than those in $\alpha$, we obtain $[\Delta \alpha/\alpha ] = (-1.7 \pm 1.4) \times 10^{-6}$ over a lookback time of 6.7 Gyrs.

Observation of the v′=8←v=0 vibrational overtone in cold trapped HD+

We report the observation of the hitherto undetected v′=8←v=0 vibrational overtone in trapped HD+ molecular ions, sympathetically cooled by laser-cooled Be+ ions. The overtone is excited using 782 nm laser radiation, after which HD+ ions in v=8 are photodissociated by the 313 nm laser used for Be+ cooling. The concomitant loss of HD+ is detected by the method of secular excitation (Roth et al. in Phys. Rev. A. 74:040501(R), 2006). We furthermore present details of the experimental setup, and we show that results from spectroscopy of v′=8←v=0 overtones in combination with accurate ab initio calculations may yield a new value for the proton–electron mass ratio with an accuracy of order 1 ppb.

The Constancy of the Constants of Nature: Updates

The current observational and experimental bounds on the time variation of the constants of nature (the fine structure constant $\alpha$, the gravitational constant $G$ and the proton-electron mass ratio $\mu=m_p/m_e$) are reviewed.

A slant on warped extra dimensions

We propose an orbifolded, warped, extra dimension scenario in which the visible brane is not parallel to the hidden brane. This leads automatically to Lorentz violation in the visible, four-dimensional world. The background solution to the Einstein equations is a function of a parameter that can be identified with the amount of ‘tilting’ of the brane. The cosmological constant is found to coincide with the classic Randall–Sundrum value to the first order in this tilt. Lorentz violating effects induced in the Standard Model are considered. We find that the strongest constraint on the tilt comes from determinations of the electron–proton mass ratio in six quasar spectra (four optical and two radio). Measurements of a third radio source could improve this by an order of magnitude.

CONSTRAINING CHANGES IN THE PROTON-ELECTRON MASS RATIO WITH INVERSION AND ROTATIONAL LINES

We report deep Green Bank Telescope (GBT) spectroscopy in the redshifted NH$_3$~(1,1), CS~1-0 and H$_2$CO~0$_{\rm 00}$-1$_{\rm 01}$ lines from the $z \sim 0.685$ absorber towards B0218+357. The inversion (NH$_3$) and rotational (CS, H$_2$CO) line frequencies have different dependences on the proton-electron mass ratio $\mu$, implying that a comparison between the line redshifts is sensitive to changes in $\mu$. A joint 3-component fit to the NH$_3$, CS, and H$_2$CO lines yields $[\Delta \mu/\mu] = (-3.5 \pm 1.2) \times 10^{-7}$, from $z \sim 0.685$ to today, where the error includes systematic effects from comparing lines from different species and possible frequency-dependent source morphology. Two additional sources of systematic error remain, due to time variability in the source morphology and velocity offsets between nitrogen-bearing and carbon-bearing species. We find no statistically-significant ($\ge 3 \sigma$) evidence for changes in $\mu$, and obtain the stringent $3\sigma$ constraint, $[\Delta \mu/\mu] < 3.6 \times 10^{-7}$, over 6.2~Gyrs; this is the best present limit on temporal changes in $\mu$ from any technique, and for any lookback time, by a factor $\gtrsim 5$.

PROBING FUNDAMENTAL CONSTANT EVOLUTION WITH REDSHIFTED CONJUGATE-SATELLITE OH LINES

We report Westerbork Synthesis Radio Telescope and Arecibo Telescope observations of the redshifted satellite OH-18cm lines at $z \sim 0.247$ towards PKS1413+135. The "conjugate" nature of these lines, with one line in emission and the other in absorption, but with the same shape, implies that the lines arise in the same gas. The satellite OH-18cm line frequencies also have different dependences on the fine structure constant $\alpha$, the proton-electron mass ratio $\mu = m_p/m_e$, and the proton gyromagnetic ratio $g_p$. Comparisons between the satellite line redshifts in conjugate systems can hence be used to probe changes in $\alpha$, $\mu$, and $g_p$, with few systematic effects. The technique yields the expected null result when applied to Cen.A, a nearby conjugate satellite system. For the $z \sim 0.247$ system towards PKS1413+135, we find, on combining results from the two telescopes, that $[\Delta G/G] = (-1.18 \pm 0.46) \times 10^{-5}$ (weighted mean), where $G = g_p [\mu \alpha^2]^{1.85}$; this is tentative evidence (with $2.6 \sigma$ significance, or at 99.1% confidence) for a smaller value of $\alpha$, $\mu$, and/or $g_p$ at z~0.247, i.e. at a lookback time of ~2.9 Gyrs. If we assume that the dominant change is in $\alpha$, this implies $[\Delta \alpha /\alpha ] = (-3.1 \pm 1.2) \times 10^{-6}$. We find no evidence that the observed offset might be produced by systematic effects, either due to observational or analysis procedures, or local conditions in the molecular cloud.

Chemistry as a function of the fine-structure constant and the electron-proton mass ratio

In standard computations in theoretical quantum chemistry the accepted values of the fundamental physical constants are assumed. Alternatively, the tools of computational quantum chemistry can be used to investigate hypothetical chemistry that would result from different values of these constants, given the same physical laws. In this work, the dependence of a variety of basic chemical quantities on the values of the fine-structure constant and the electron-proton mass ratio is explored. In chemistry, the accepted values of both constants may be considered small, in the sense that their increase must be substantial to seriously impact bond energies. It is found that if the fine-structure constant were larger, covalent bonds between light atoms would be weaker, and the dipole moment and hydrogen-bonding ability of water would be reduced. Conversely, an increase in the value of the electron-proton mass ratio increases dissociation energies in molecules such as ${\mathrm{H}}_{2}$, ${\mathrm{O}}_{2}$, and CO${}_{2}$. Specifically, a sevenfold increase in the fine-structure constant decreases the strength of the O--H bond in the water molecule by 7 kcal mol${}^{\ensuremath{-}1}$ while reducing its dipole moment by at least $10%$, whereas a 100-fold increase in the electron-proton mass ratio increases the same bond energy by 11 kcal mol${}^{\ensuremath{-}1}$.

PROBING FUNDAMENTAL CONSTANT EVOLUTION WITH NEUTRAL ATOMIC GAS LINES

We have detected narrow HI 21cm and CI absorption at $z \sim 1.4 - 1.6$ towards Q0458$-$020 and Q2337$-$011, and use these lines to test for possible changes in the fine structure constant $\alpha$, the proton-electron mass ratio $\mu$, and the proton gyromagnetic ratio $g_p$. A comparison between the HI 21cm and CI line redshifts yields $\Delta X/X = [+6.8 \pm 1.0] \times 10^{-6}$ over $0 < <z> \le 1.46$, where $X = g_p \alpha^2/\mu$, and the errors are purely statistical, from the gaussian fits. The simple line profiles and the high sensitivity of the spectra imply that statistical errors in this comparison are an order of magnitude lower than in previous studies. Further, the CI lines arise in cold neutral gas that also gives rise to HI 21cm absorption, and both background quasars are core-dominated, reducing the likelihood of systematic errors due to local velocity offsets between the hyperfine and resonance lines. The dominant source of systematic error lies in the absolute wavelength calibration of the optical spectra, which appears uncertain to $\sim 2$ km/s, yielding a maximum error in $\Delta X/X$ of $\sim 6.7 \times 10^{-6}$. Including this, we obtain $\Delta X/X = [+6.8 \pm 1.0 (statistical) \pm 6.7 (max. systematic)] \times 10^{-6}$ over $0 < <z> \le 1.46$. Using literature constraints on $\Delta \mu/\mu$, this is inconsistent with claims of a smaller value of $\alpha$ from the many-multiplet method, unless fractional changes in $g_p$ are larger than those in $\alpha$ and $\mu$.

Prospects for application of ultracoldSr2molecules in precision measurements

Precision measurements with ultracold molecules require development of robust and sensitive techniques to produce and interrogate the molecules. With this goal, we theoretically analyze factors that affect frequency measurements between rovibrational levels of the ${\mathrm{Sr}}_{2}$ molecule in the electronic ground state. This measurement can be used to constrain the possible time variation of the proton-electron mass ratio. ${\mathrm{Sr}}_{2}$ is expected to be a strong candidate for achieving high precision due to the spinless nature and ease of cooling and perturbation-free trapping of Sr [T. Zelevinsky et al., Phys. Rev. Lett. 100, 043201 (2008)]. The analysis includes calculations of two-photon transition dipole moments between deeply and weakly bound vibrational levels, lifetimes of intermediate excited states, and Stark shifts of the vibrational levels by the optical lattice field, including possibilities of Stark-cancellation trapping.

Constants of Nature from the Dynamics of Time

An archetypal model for the constants of nature is found from the ancient geometry of the the Cosmological Circle and is related to Plato's cosmology, with its dynamics and harmonics of time cycles. The inverse fine-structure constant and the proton-electron mass ratio are calculated, connecting fundamental mathematical constants of geometry with the latest theoretical and experimental values of these physical constants. Continuing in the tradition of George Gamow's suggestion, Since the works of Sir Arthur Eddington, it has become customary to discuss from time to time the numerical relations between various fundamental constants of nature. Although until today such discussions have not led to any practical results - that is, to any valuable road signs toward further development of the theory of the still unclear fundamental facts in physics - it may be of some interest to survey the present status of this 'clairvoyant' branch of science.

DO THE FUNDAMENTAL CONSTANTS CHANGE WITH TIME?

Comparisons between the redshifts of spectral lines from cosmologically-distant galaxies can be used to probe temporal changes in low-energy fundamental constants like the fine structure constant and the proton–electron mass ratio. Here, we review the results from, and the advantages and disadvantages of, the best techniques using this approach, before focussing on a new method, based on conjugate satellite OH lines, that appears to be less affected by systematic effects and hence holds much promise for the future.

Prospects for precision measurements on ammonia molecules in a fountain

The recent demonstration of cooling and manipulation techniques for molecules offer newpossibilities for precision measurements in molecules. Here, we present the design of a molecularfountain based on a Stark decelerated molecular beam. In this fountain, ammonia molecules aredecelerated to a few meter per second, cooled to sub microKelvin temperatures and subsequentlylaunched. The molecules fly upwards some 30 cm before falling back under gravity, thereby passing amicrowave cavity twice – as they fly up and as they fall back down. The effective interrogationtime in such a Ramsey type measurement scheme includes the entire flight time between the twotraversals through the driving field, which is on the order of a 1/2 second. We present numericalsimulations of the trajectories through the decelerator and estimate the expected count rate. Wepresent an evaluation of the expected stability and accuracy for the inversion transition in15NH3 around 22.6 GHz. The estimated frequency instability is \(7\times10^{-12}~\tau^{-1/2}\), with τ being the measurement time in seconds. With a careful design ofthe interogation zone, systematic frequency shifts are kept below 10-14. Besides serving as aproof-of-principle, these measurements may be used as a test of the time-variation of fundamentalconstants using the sensitivity of the tunneling motion to a change of the proton-electron massratio.

Varying alpha: New constraints from seasonal variations

We analyze the constraints obtained from new atomic clock data on the possible time variation of the fine structure ``constant'' and the electron-proton mass ratio, and show how they are strengthened when the seasonal variation of the Sun's gravitational field at the Earth's surface is taken into account. We compare these bounds with those obtainable from tests of the weak equivalence principle and high redshift observations of quasar absorption spectra.

New Limits on Coupling of Fundamental Constants to Gravity UsingSr87Optical Lattice Clocks

The 1S0-3P0 clock transition frequency nuSr in neutral 87Sr has been measured relative to the Cs standard by three independent laboratories in Boulder, Paris, and Tokyo over the last three years. The agreement on the 1 x 10(-15) level makes nuSr the best agreed-upon optical atomic frequency. We combine periodic variations in the 87Sr clock frequency with 199Hg+ and H-maser data to test local position invariance by obtaining the strongest limits to date on gravitational-coupling coefficients for the fine-structure constant alpha, electron-proton mass ratio mu, and light quark mass. Furthermore, after 199Hg+, 171Yb+, and H, we add 87Sr as the fourth optical atomic clock species to enhance constraints on yearly drifts of alpha and mu.