Search

We present a class of models in which the coupling of the photon to an ultralight scalar field that has a time-dependent vacuum expectation value causes the fine structure constant to oscillate in time. The scalar field is assumed to constitute all or part of the observed dark matter. Its mass is protected against radiative corrections by a discrete $\mathbb{Z}_N$ exchange symmetry that relates the Standard Model to several copies to itself. The abundance of dark matter is set by the misalignment mechanism. We show that the oscillations in the fine structure constant are large enough to be observed in current and near-future experiments., 15 pages, 5 figures. Matches the version published in PRD

Inside a quantum spin ice, the constant that defines electromagnetic interactions is 10 times larger than normal, according to calculations.

The recently improved observation of the fine structure constant has led to a negative $2.4\sigma$ anomaly of electron $g-2$. Combined with the long-existing positive $4.2\sigma$ discrepancy of the muon anomalous magnetic moment, it is interesting and difficult to explain these two anomalies with a consistent model without introducing flavor violations. We show that they can be simultaneously explained in the inverse seesaw extended next-to-minimal supersymmetric standard model (ISS-NMSSM) by the Higgsino--sneutrino contributions to $(g-2)_e$ and $(g-2)_\mu$. The spectrum features prefer light $\mu$, which can predict $m_Z$ naturally, and it is not difficult to obtain a $\tau$-type sneutrino dark matter candidate that is compatible with the observed dark matter relic density and the bounds from dark matter direct detection experiments. Due to the compressed spectra and the undetectable decay mode of selectrons, they can evade the current Large Hadron Collider (LHC) constraints., Comment: 37 pages, 11 figures

We performed a search for a new generic X boson, which could be a scalar (S), pseudoscalar (P), vector (V), or an axial vector (A) particle produced in the 100 GeV electron scattering off nuclei, e^{-}Z→e^{-}ZX, followed by its invisible decay in the NA64 experiment at CERN. No evidence for such a process was found in the full NA64 dataset of 2.84×10^{11} electrons on target. We place new bounds on the S, P, V, A coupling strengths to electrons, and set constraints on their contributions to the electron anomalous magnetic moment a_{e}, |Δa_{X}|≲10^{-15}-10^{-13} for the X mass region 1 MeV≲m_{X}≲1 GeV. These results are an order of magnitude more sensitive compared to the current accuracy on a_{e} from the electron g-2 experiments and recent high-precision determination of the fine structure constant.

We propose a simple model based on the assumption that the varying fine structure constant $\ensuremath{\alpha}$ is an effect of the cosmological expansion to investigate the relation between the varying $\ensuremath{\alpha}$ and the cosmological components. For a spatially flat, homogeneous, and isotropic universe, the current proportion of cosmological components and age of the universe predicted by the model are consistent with the cosmological observations. Furthermore, the predicted current variation rate of $\ensuremath{\alpha}$ is also close to the atomic clock measurements. For the early universe, we predict a very strict constraint, which is compatible with the upper limit given by the investigations of cosmic microwave background and big bang nucleosynthesis.

Peik and Tamm [Europhys. Lett. 61, 181 (2003)] proposed a nuclear clock based on the isomeric transition between the ground state and the first excited state of thorium-229. This transition was recognized as a potentially sensitive probe of possible temporal variation of the fine-structure constant, $\ensuremath{\alpha}$. The sensitivity to such a variation can be determined from measurements of the mean-square charge radius and quadrupole moment of the different isomers. However, current measurements of the quadrupole moment are yet to achieve an accuracy high enough to resolve nonzero sensitivity. Here we determine this sensitivity using existing measurements of the change in the mean-square charge radius, coupled with the ansatz of constant nuclear density. The enhancement factor for $\ensuremath{\alpha}$ variation is $K=\ensuremath{-}(0.82\ifmmode\pm\else\textpm\fi{}0.25)\ifmmode\times\else\texttimes\fi{}{10}^{4}$. For the current experimental limit, $\ensuremath{\delta}\ensuremath{\alpha}/\ensuremath{\alpha}\ensuremath{\lesssim}{10}^{\ensuremath{-}17}$ per year, the corresponding frequency shift is $\ensuremath{\sim}200$ Hz per year. This shift is six orders of magnitude larger than the projected accuracy of the nuclear clock, paving the way for increased accuracy of the determination of $\ensuremath{\delta}\ensuremath{\alpha}$ and interaction strength with low-mass scalar dark matter. We verify that the constant-nuclear-density ansatz is supported by nuclear theory and propose how to verify it experimentally. We also consider a possible effect of the octupole deformation on the sensitivity to $\ensuremath{\alpha}$ variation and calculate the effects of $\ensuremath{\alpha}$ variation in a number of M\"ossbauer transitions.

We derive an electrically charged static black hole spacetime of the Einstein-Euler-Heisenberg theory, in terms of the Pleba\ifmmode \acute{n}\else \'{n}\fi{}ski dual variables. This solution is a nonlinear electromagnetic generalization of the Reissner-Nordstr\"om solution, and it is characterized by the mass $M$, the electric charge $Q$ of the black hole, and the Euler-Heisenberg nonlinear constant, which includes the fine structure constant $\ensuremath{\alpha}$. We study all possible equatorial trajectories of test particles. Moreover, the orbits of photons are analyzed by means of the effective Pleba\ifmmode \acute{n}\else \'{n}\fi{}ski pseudometric related to the geometrical metric and to the electromagnetic energy-momentum tensor. The shape of the shadow of the black hole is also presented and discussed.

I consider quantum electrodynamics with many electrons in 2+1 space-time dimensions at finite temperature. The relevant dimensionless interaction parameter for this theory is the fine structure constant divided by the temperature. The theory is solvable at any value of the coupling, in particular for very weak (high temperature) and infinitely strong coupling (corresponding to the zero temperature limit). Concentrating on the photon, each of its physical degrees of freedom at infinite coupling only contributes half of the free-theory value to the entropy. These fractional degrees of freedom are reminiscent of what has been observed in other strongly coupled systems (such as N=4 supersymmetric Yang-Mills theory), and bear similarity to the fractional quantum Hall effect, potentially suggesting connections between these phenomena. The results found for (2+1)-dimensional QED are fully consistent with the expectations from particle-vortex duality.

Ultralight scalars can extract rotational energy from astrophysical black holes through superradiant instabilities, forming macroscopic boson clouds. This process is most efficient when the Compton wavelength of the boson is comparable to the size of the black hole horizon, i.e. when the "gravitational fine structure constant" $\alpha\equiv G \mu M/\hbar c\sim 1$. If the black hole/cloud system is in a binary, tidal perturbations from the companion can produce resonant transitions between the energy levels of the cloud, depleting it by an amount that depends on the nature of the transition and on the parameters of the binary. Previous cloud depletion estimates considered binaries in circular orbit and made the approximation $\alpha\ll 1$. Here we use black hole perturbation theory to compute instability rates and decay widths for generic values of $\alpha$, and we show that this leads to much larger cloud depletion estimates when $\alpha \gtrsim 0.1$. We also study eccentric binary orbits. We show that in this case resonances can occur at all harmonics of the orbital frequency, significantly extending the range of frequencies where cloud depletion may be observable with gravitational wave interferometers., Comment: 12 pages, 6 figures. v2: references added, matches published version

The fine-structure constant, $\alpha$, controls the strength of the electromagnetic interaction. There are extensions of the standard model in which $\alpha$ is dynamical on cosmological length and time-scales. The physics of the cosmic microwave background (CMB) depends on the value of $\alpha$. The effects of spatial variation in $\alpha$ on the CMB are similar to those produced by weak lensing: smoothing of the power spectrum, and generation of non-Gaussian features. These would induce a bias to estimates of the weak-lensing potential power spectrum of the CMB. Using this effect, Planck measurements of the temperature and polarization power spectrum, as well as estimates of CMB lensing, are used to place limits (95% C. L.) on the amplitude of a scale-invariant angular power spectrum of $\alpha$ fluctuations relative to the mean value ($C_L^{\alpha}=A^\alpha_{\rm SI}/[L(L+1)]$) of $A^\alpha_{\rm SI}\leq 1.6 \times 10^{-5}$. The limits depend on the assumed shape of the $\alpha$-fluctuation power spectrum. For example, for a white noise angular power spectrum ($C_L^{\alpha}=A^\alpha_{\rm WN}$), the limit is $A^\alpha_{\rm WN}\leq 2.3 \times 10^{-8}$. It is found that the response of the CMB to $\alpha$ fluctuations depends on a separate-universe approximation, such that theoretical predictions are only reliable for $\alpha$ multipoles with $L\lesssim 100$ . An optimal trispectrum estimator can be constructed and it is found that it is only marginally more sensitive than lensing techniques for Planck but significantly more sensitive when considering the next generation of experiments. For a future CMB experiment with cosmic-variance limited polarization sensitivity (e.g., CMB-S4), the optimal estimator could detect $\alpha$ fluctuations with $A^\alpha_{\rm SI}>1.9 \times 10^{-6}$ and $A^\alpha_{\rm WN} > 1.4 \times 10^{-9}$., Comment: 21 pages, 11 figures, comments welcome

There is a growing interest in astrophysical tests of the stability of dimensionless fundamental couplings, such as the fine-structure constant $\alpha$, as an optimal probe of new physics. The imminent arrival of the ESPRESSO spectrograph will soon enable significant gains in the precision and accuracy of these tests and widen the range of theoretical models that can be tightly constrained. Here we illustrate this by studying proposed extensions of the Bekenstein-type models for the evolution of $\alpha$ that allow different couplings of the scalar field to both dark matter and dark energy. We use a combination of current astrophysical and local laboratory data (from tests with atomic clocks) to show that these couplings are constrained to parts per million level, with the constraints being dominated by the atomic clocks. We also quantify the expected improvements from ESPRESSO and other future spectrographs, and briefly discuss possible observational strategies, showing that these facilities can improve current constraints by more than an order of magnitude., Comment: 11 pages, 7 figures

One of the amazing properties of graphene is the ultrarelativistic behavior of its loosely bound electrons, mimicking massless fermions that move with a constant velocity, inversely proportional to a fine-structure constant ${\ensuremath{\alpha}}_{g}$ of the order of unity. The effective interaction between these quasiparticles is, however, better controlled by the coupling parameter ${\ensuremath{\alpha}}_{g}^{*}={\ensuremath{\alpha}}_{g}/\ensuremath{\epsilon}$, which accounts for the dynamic screening due to the complex permittivity $\ensuremath{\epsilon}$ of the many-valence electron system. This concept was introduced in a couple of previous studies [Reed et al., Science 330, 805 (2010) and Gan et al., Phys. Rev. B 93, 195150 (2016)], where inelastic x-ray scattering measurements on crystal graphite were converted into an experimentally derived form of ${\ensuremath{\alpha}}_{g}^{*}$ for graphene, over an energy-momentum region on the $\mathrm{eV}\phantom{\rule{0.16em}{0ex}}\AA{}{}^{\ensuremath{-}1}$ scale. Here, an accurate theoretical framework is provided for ${\ensuremath{\alpha}}_{g}^{*}$, using time-dependent density-functional theory in the random-phase approximation, with a cutoff in the interaction between excited electrons in graphene, which translates to an effective interlayer interaction in graphite. The predictions of the approach are in excellent agreement with the above-mentioned measurements, suggesting a calibration method to substantially improve the experimental derivation of ${\ensuremath{\alpha}}_{g}^{*}$, which tends to a static limiting value of $\ensuremath{\sim}0.14$. Thus, the ab initio calibration procedure outlined demonstrates the accuracy of perturbation expansion treatments for the two-dimensional gas of massless Dirac fermions in graphene, in parallel with quantum electrodynamics.

In this work we have studied the lithium problem in nonstandard cosmological models. In particular, by using the public code ALTERBBN, we have included in the computation of the primordial light nuclei abundances, the effects of the inclusion of dark energy and dark entropy, along with the variation of the fine structure constant and the Higgs vacuum expectation value. In order to set constrains on the variation of the fundamental constants we have compared our theoretical results with the available observational data. We have found that the lithium abundance is reduced for not-null variation at the 3σ-level of both constants., Facultad de Ciencias Astronómicas y Geofísicas, Facultad de Ciencias Exactas

We calculate ionization energies and fundamental vibrational transitions for H_{2}^{+}, D_{2}^{+}, and HD^{+} molecular ions. The nonrelativistic quantum electrodynamics expansion for the energy in terms of the fine structure constant α is used. Previous calculations of orders mα^{6} and mα^{7} are improved by including second-order contributions due to the vibrational motion of nuclei. Furthermore, we evaluate the largest corrections at the order mα^{8}. That allows us to reduce the fractional uncertainty to the level of 7.6×10^{-12} for fundamental transitions and to 4.5×10^{-12} for the ionization energies.

We investigate the transition between the fine structure levels of the ground state, $3p{\phantom{\rule{0.16em}{0ex}}}^{2}{P}_{1/2}\ensuremath{\rightarrow}3p{\phantom{\rule{0.16em}{0ex}}}^{2}{P}_{3/2}$, of the highly charged Al-like $^{51}\mathrm{V}^{10+},\phantom{\rule{0.16em}{0ex}}^{53}\mathrm{Cr}^{11+},\phantom{\rule{0.16em}{0ex}}^{55}\mathrm{Mn}^{12+},\phantom{\rule{0.16em}{0ex}}^{57}\mathrm{Fe}^{13+},\phantom{\rule{0.16em}{0ex}}^{59}\mathrm{Co}^{14+},\phantom{\rule{0.16em}{0ex}}^{61}\mathrm{Ni}^{15+}$, and $^{63}\mathrm{Cu}^{16+}$ ions for frequency standards. To comprehend them as prospective atomic clocks, we determine their transition wavelengths, quality factors, and various plausible systematics during the measurements. Since most of these ions have nuclear spin $I=3/2$, uncertainties due to dominant quadrupole shifts can be evaded in the $F=0$ hyperfine level of the $3p{\phantom{\rule{0.16em}{0ex}}}^{2}{P}_{3/2}$ state. Other dominant systematics such as quadratic Stark and black-body radiation shifts have been evaluated precisely demonstrating the feasibility of achieving high accuracy, below ${10}^{\ensuremath{-}19}$ fractional uncertainty, atomic clocks using the above transitions. Moreover, relativistic sensitivity coefficients are determined to find out the aptness of these proposed clocks to investigate possible temporal variation of the fine structure constant. To carry out these analysis, a relativistic coupled-cluster method considering Dirac-Coulomb-Breit Hamiltonian along with lower-order quantum electrodynamics interactions is employed and many spectroscopic properties are evaluated. These properties are also of immense interest for astrophysical studies.

We report a search for a dark vector gauge boson U' that couples to quarks in the decay chain D*(+) -> D-0 pi(+), D-0 -> K-S(0) eta, eta -> U'gamma, U' -> pi(+)pi- No signal is found and we set a mass-dependent limit on the baryonic fine structure constant of 10(-3)-10(-2) in the U' mass range of 290 to 520 MeV/c(2). This analysis is based on a data sample of 976 fb(-1) collected by the Belle experiment at the KEKB asymmetric-energy e(+)e(-) collider.

We propose an improved methodology to constrain spatial variations of the fine structure constant using clusters of galaxies. We use the {\it Planck} 2013 data to measure the thermal Sunyaev-Zeldovich effect at the location of 618 X-ray selected clusters. We then use a Monte Carlo Markov Chain algorithm to obtain the temperature of the Cosmic Microwave Background at the location of each galaxy cluster. When fitting three different phenomenological parameterizations allowing for monopole and dipole amplitudes in the value of the fine structure constant we improve the results of earlier analysis involving clusters and the CMB power spectrum, and we also found that the best-fit direction of a hypothetical dipole is compatible with the direction of other known anomalies. Although the constraining power of our current datasets do not allow us to test the indications of a fine-structure constant dipole obtained though high-resolution optical/UV spectroscopy, our results do highlight that clusters of galaxies will be a very powerful tool to probe fundamental physics at low redshift., 11 pages, 5 figures and 3 tables. Accepted for publication in Physical Review D

Transitions among the first three low-lying states in the highly charged $\mathrm{W}^{13+}, \mathrm{Ir}^{16+}$, and $\mathrm{Pt}^{17+}$ ions are found to be strongly forbidden with wavelengths in the optical regime. By determining their energy levels, lifetimes, and other spectroscopic properties that are decisive quantities for estimating dominant systematics due to stray electromagnetic interactions in an experiment, we demonstrate that it can be possible to measure frequencies of the lowest forbidden transitions below a ${10}^{\ensuremath{-}19}$ precision level in the above ions, and hence, they seem to be suitable for frequency standards. We employ a sophisticated relativistic coupled cluster method to carry out calculations of these properties of the above states involving $4f$- and $5s$-core orbitals. We also found, by estimating their relativistic sensitivity coefficients, that these clock transitions can be highly sensitive to the tiny drift in the fine-structure constant ${\ensuremath{\alpha}}_{e}$. Consequently, a clock based on one of these ions, particularly $\mathrm{Pt}^{17+}$, could be used for corroborating the hypothesis of temporal and spatial variation in ${\ensuremath{\alpha}}_{e}$.

A weighted difference of the $g$-factors of the Li- and H-like ion of the same element is studied and optimized in order to maximize the cancellation of nuclear effects. To this end, a detailed theoretical investigation is performed for the finite nuclear size correction to the one-electron $g$-factor, the one- and two-photon exchange effects, and the QED effects. The coefficients of the $Z\alpha$ expansion of these corrections are determined, which allows us to set up the optimal definition of the weighted difference. It is demonstrated that, for moderately light elements, such weighted difference is nearly free from uncertainties associated with nuclear effects and can be utilized to extract the fine-structure constant from bound-electron $g$-factor experiments with an accuracy competitive with or better than its current literature value., Comment: 11 pages, 3 figures, 6 tables. arXiv admin note: text overlap with arXiv:1509.08260

Modifications of gravity generated by a multiplicative coupling of a scalar field to the electromagnetic Lagrangian lead to a breaking of Einstein equivalence principle (EEPB) as well as to variations of fundamental constants. In these theoretical frameworks, deviations of standard values of the fine structure constant, $\Delta \alpha/\alpha=\phi$, and of the cosmic distance duality relation, $D_L(1+z)^{-2}/D_A=\eta=1$, where $D_L$ and $D_A$ are the luminosity and angular diameter distances, respectively, are unequivocally linked. In this paper, we search for cosmological signatures of the EEPB by using angular diameter distance from galaxy clusters, obtained via their Sunyaev-Zeldovich effect (SZE) and X-ray observations, and distance modulus of type Ia supernovae (SNe Ia). The crucial point here is that we take into account the dependence of the SZE/X-ray technique with $\phi$ and $\eta$. Our new results show no indication of the EEPB., Comment: 2 figures, 5pages, To appear in Physical Review D

We critically assess recent claims suggesting that upper limits on the time variation of the fine-structure constant tightly constrain the coupling of a dark energy scalar field to the electromagnetic sector, and, indirectly, the violation of the weak equivalence principle. We show that such constraints depend crucially on the assumed priors, even if the dark energy was described by a dynamical scalar field with a constant equation of state parameter $w$ linearly coupled to the electromagnetic sector through a dimensionless coupling $\zeta$. We find that, although local atomic clock tests, as well as other terrestrial, astrophysical and cosmological data, put stringent bounds on $|\zeta| {\sqrt {|w+1|}}$, the time variation of the fine-structure constant cannot be used to set or to improve upper limits on $|\zeta|$ or $|w+1|$ without specifying priors, consistent but not favoured by current data, which strongly disfavour low values of $|w+1|$ or $|\zeta|$, respectively. We briefly discuss how this might change with a new generation of high-resolution ultra-stable spectrographs, such as ESPRESSO and ELT-HIRES, in combination with forthcoming missions to map the geometry of the Universe, such as Euclid, or to test the equivalence principle, such as MICROSCOPE or STEP., Comment: 7 pages, 5 figures

Dirac strings in spin ices are lines of reversed dipoles joining two quasiparticle excitations. These excitations behave as unbound emergent monopoles if the tension of Dirac strings vanishes. In this Letter, analytical and numerical analysis are used to study the dynamics of two-dimensional dipolar spin ices, artificially created analogs of bulk spin ice, in the regime of bound monopoles. It is shown that, in this regime, strings, rather than monopoles, are effective degrees of freedom explaining the finite-width band of Pauling states. A measurable prediction of path-time dependence of endpoints of a stretched and, then, released Dirac string is made and verified via simulations. It is shown that string dynamics is defined by the characteristic tension-to-mass ratio, which is determined by the fine structure constant and lattice dependent parameter. It is proposed to use string tension to achieve spontaneous magnetic currents. A concept of an energy storing device on the basis of this principle is proposed and illustrated by an experimental demonstration. A scheme of independent measurement at the nanoscale is proposed.

Astrophysical tests of the stability of fundamental couplings, such as the fine-structure constant $\alpha$, are a powerful probe of new physics. Recently these measurements, combined with local atomic clock tests and Type Ia supernova and Hubble parameter data, were used to constrain the simplest class of dynamical dark energy models where the same degree of freedom is assumed to provide both the dark energy and (through a dimensionless coupling, $\zeta$, to the electromagnetic sector) the $\alpha$ variation. One caveat of these analyses was that it was based on fiducial models where the dark energy equation of state was described by a single parameter (effectively its present day value, $w_0$). Here we relax this assumption and study broader dark energy model classes, including the Chevallier-Polarski-Linder and Early Dark Energy parametrizations. Even in these extended cases we find that the current data constrains the coupling $\zeta$ at the $10^{-6}$ level and $w_0$ to a few percent (marginalizing over other parameters), thus confirming the robustness of earlier analyses. On the other hand, the additional parameters are typically not well constrained. We also highlight the implications of our results for constraints on violations of the Weak Equivalence Principle and improvements to be expected from forthcoming measurements with high-resolution ultra-stable spectrographs., Comment: 13 pages, 11 figures. arXiv admin note: text overlap with arXiv:1508.06157, arXiv:1505.02196

Iridium ions near $4f\ensuremath{-}5s$ level crossings are the leading candidates for a new type of atomic clocks with a high projected accuracy and a very high sensitivity to the temporal variation of the fine structure constant $\ensuremath{\alpha}$. To identify spectra of these ions in experiment accurate calculations of the spectra and electromagnetic transition probabilities should be performed. Properties of the $4f\text{-core-excited}$ states in ${\mathrm{Ir}}^{16+},{\mathrm{Ir}}^{17+}$, and ${\mathrm{Ir}}^{18+}$ ions are evaluated using relativistic many-body perturbation theory and Hartree-Fock-relativistic method (COWAN code). We evaluate excitation energies, wavelengths, oscillator strengths, and transition rates. Our large-scale calculations included the following set of configurations: $4{f}^{14}5s,4{f}^{14}5p,4{f}^{13}5{s}^{2},4{f}^{13}5{p}^{2},4{f}^{13}5s5p,4{f}^{12}5{s}^{2}5p$, and $4{f}^{12}5s5{p}^{2}$ in Pm-like ${\mathrm{Ir}}^{16+}$; $4{f}^{14},4{f}^{13}5s,4{f}^{13}5p,4{f}^{12}5{s}^{2},4{f}^{12}5s5p$, and $4{f}^{12}5{p}^{2}$ in Nd-like ${\mathrm{Ir}}^{17+}$; and $4{f}^{13},4{f}^{12}5s,4{f}^{12}5p,4{f}^{11}5{s}^{2}$, and $4{f}^{11}5s5p$ in Pr-like ${\mathrm{Ir}}^{18+}$. The $5s\ensuremath{-}5p$ transitions are illustrated by the synthetic spectra in the 180--200 \AA{} range. Large contributions of magnetic-dipole transitions to lifetimes of low-lying states in the region below 2.5 Ry are demonstrated.

Background: A signature of many dynamical models of dark energy is that they admit variation in the fine structure constant $\ensuremath{\alpha}$ over cosmological time scales.Purpose: We reconsider the analysis of the sensitivity of neutron resonance energies ${E}_{i}$ to changes in $\ensuremath{\alpha}$ with a view to resolving uncertainties that plague earlier treatments.Methods: We point out that with more appropriate choices of nuclear parameters, the standard estimate (from Damour and Dyson) of the sensitivity for resonances in $\mathrm{Sm}$ is increased by a factor of 2.5. We go on to identify and compute excitation, Coulomb, and deformation corrections. To this end, we use deformed Fermi density distributions fitted to the output of Hartree-Fock (HF) + BCS calculations (with both the SLy4 and ${\mathrm{SkM}}^{*}$ Skyrme functionals), the energetics of the surface diffuseness of nuclei, and thermal properties of their deformation. We also invoke the eigenstate thermalization hypothesis, performing the requisite microcanonical averages with two phenomenological level densities which, via the leptodermous expansion of the level density parameter, include the effect of increased surface diffuseness. Theoretical uncertainties are assessed with the inter-model prescription of Dobaczewski et al. [J. Phys. G: Nucl. Part. Phys. 41, 074001 (2014)].Results: The corrections diminish the revised $\mathrm{Sm}$ sensitivity but not by more than 25%. Subject to a weak and testable restriction on the change in ${m}_{q}/\mathrm{\ensuremath{\Lambda}}$ (relative to the change in $\ensuremath{\alpha})$ since the time when the Oklo reactors were active $({m}_{q}$ is the average of the $\text{u}$ and $\text{d}$ current quark masses, and $\mathrm{\ensuremath{\Lambda}}$ is the mass scale of quantum chromodynamics), we deduce that $|{\ensuremath{\alpha}}_{\text{Oklo}}\ensuremath{-}{\ensuremath{\alpha}}_{\text{now}}|l1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}{\ensuremath{\alpha}}_{\text{now}}$ (95% confidence level). The corresponding bound on the present-day time variation of $\ensuremath{\alpha}$ is tighter than the best limit to date from atomic clock experiments.Conclusions: The order of magnitude of our Oklo bound on changes in $\ensuremath{\alpha}$ is reliable. It is one order of magnitude lower than the Oklo-based bound most commonly adopted in earlier attempts to identify phenomenologically successful models of $\ensuremath{\alpha}$ variation.

This paper proposes a systematic study of cosmological signatures of modifications of gravity via the presence of a scalar field with a multiplicative coupling to the electromagnetic Lagrangian. We show that, in this framework, variations of the fine structure constant, violations of the distance duality relation, evolution of the cosmic microwave background (CMB) temperature and CMB distortions are intimately and unequivocally linked. This enables one to put very stringent constraints on possible violations of the distance duality relation, on the evolution of the CMB temperature and on admissible CMB distortions using current constraints on the fine structure constant. Alternatively, this offers interesting possibilities to test a wide range of theories of gravity by analysing several datasets concurrently. We discuss results obtained using current data as well as some forecasts for future data sets such as those coming from EUCLID or the SKA., Comment: 14 pages, 4 figures, matched published version. Note: title changed upon suggestion of PRD editors

We analyze the behavior of blackbody radiation in theories of electromagnetism which allow the electron charge and the fine structure constant to vary in space and time. We show that such theories can be expressed as relativistic generalizations of a conventional dielectric. By making the appropriate definition of the vector potential and associated gauge transformations, we can identify the equivalent of the electric and displacement fields, $\mathbf{E}$ and $\mathbf{D}$, as well as the magnetic $\mathbf{B}$ and $\mathbf{H}$ fields. We study the impact of such dielectrics on the propagation of light in the so-called ``BSBM'' theory. We examine the form of simple cosmological solutions and conclude that no changes are created to the standard cosmological evolution of the temperature and energy density of blackbody radiation. Nonetheless the matter evolution changes and the behavior of the entropy per baryon is modified, and the ratios of different dark matter components may be changed too.

Single-ion clocks yield new limits on how much the proton-to-electron mass ratio and the fine structure constant change over time.

Single-ion clocks yield new limits on how much the proton-to-electron mass ratio and the fine structure constant change over time.

Singly ionized ytterbium, with ultranarrow optical clock transitions at 467 and 436 nm, is a convenient system for the realization of optical atomic clocks and tests of present-day variation of fundamental constants. We present the first direct measurement of the frequency ratio of these two clock transitions, without reference to a cesium primary standard, and using the same single ion of 171Yb+. The absolute frequencies of both transitions are also presented, each with a relative standard uncertainty of 6 × 10 -16. Combining our results with those from other experiments, we report a threefold improvement in the constraint on the time variation of the proton-to-electron mass ratio, mu-dot/mu = 0.2(1.1) × 10-16 yr-1, along with an improved constraint on time variation of the fine structure constant, alpha-dot/alpha = -0.7(2.1) x 10-17 yr-1.

A high-precision relativistic calculations of Cd-like Nd$^{12+}$, Sm$^{14+}$ and Sn-like Pr$^{9+}$, Nd$^{10+}$ atomic properties is carried out using an approach that combines configuration interaction and a linearized coupled-cluster method. These ions have long-lived metastable states with transitions accessible by laser excitations, relatively simple electronic structure, high sensitivity to $\alpha$ variation, and stable isotopes. Breit and QED corrections were included into the calculations. Energies, transition wavelengths, electric- and magnetic-multipole reduced matrix elements, lifetimes, and sensitivity coefficients $q$ and $K$ to the variation of the fine-structure constant $\alpha$ were obtained. A detailed study of uncertainties was performed. Energies for similar Cd-like Ba$^{8+}$, La$^{9+}$, Ce$^{10+}$, Pr$^{11+}$ and Sn-like Ba$^{6+}$ ions were calculated and compared with experiment for further tests of the accuracy., Comment: 13 pages. arXiv admin note: text overlap with arXiv:1407.8272

Astrophysical tests of the stability of dimensionless fundamental couplings, such as the fine-structure constant $\alpha$, are an area of much increased recent activity, following some indications of possible spacetime variations at the few parts per million level. Here we obtain updated constraints on the Bekenstein-Sandvik-Barrow-Magueijo model, which is arguably the simplest model allowing for $\alpha$ variations. Recent accurate spectroscopic measurements allow us to improve previous constraints by about an order of magnitude. We briefly comment on the dependence of the results on the data sample, as well as on the improvements expected from future facilities., Comment: 5 pages, 2 figures

Based on the spectroscopic constants derived from highly accurate potential-energy surfaces, the SeD radical is identified as a spectroscopic probe for measuring spatial and temporal variation of fundamental physical constants such as the fine-structure constant (denoted as $\ensuremath{\alpha}=\frac{{e}^{2}}{\ensuremath{\hbar}c}$) and the proton-to-electron mass ratio (denoted as $\ensuremath{\mu}=\frac{{m}_{p}}{{m}_{e}}$). The ground state of SeD $({X}^{2}\ensuremath{\Pi})$, due to spin-orbit coupling, splits into two fine-structure multiplets ${}^{2}{\ensuremath{\Pi}}_{\frac{3}{2}}$ and ${}^{2}{\ensuremath{\Pi}}_{\frac{1}{2}}$. The potential-energy surfaces of these spin-orbit components are derived from a state of the art electronic structure method, MRCI + Q inclusive of scalar relativistic effects with the spin-orbit effects accounted for through the Breit-Pauli operator. The relevant spectroscopic data are evaluated using a Murrel-Sorbie fit to the potential-energy surfaces. The spin-orbit splitting ${\ensuremath{\omega}}_{f}$ between the two multiplets is similar in magnitude with the harmonic frequency ${\ensuremath{\omega}}_{e}$ of the diatomic molecule. The amplification factor $K$ derived from this theoretical method for this particular molecule can be as large as 350; on the lower side it can be about 34. The significantly large values of $K$ indicate that the SeD radical can be a plausible experimental candidate for measuring variation in $\ensuremath{\alpha}$ and $\ensuremath{\mu}$.

Various classes of exotic singularity models have been studied as possible mimic models for the observed recent acceleration of the universe. Here we further study one of these classes and, under the assumption that they are phenomenological toy models for the behavior of an underlying scalar field which also couples to the electromagnetic sector of the theory, obtain the corresponding behavior of the fine-structure constant $\alpha$ for particular choices of model parameters that have been previously shown to be in reasonable agreement with cosmological observations. We then compare this predicted behavior with available measurements of $\alpha$, thus constraining this putative coupling to electromagnetism. We find that values of the coupling which would provide a good fit to spectroscopic measurements of $\alpha$ are in more than three-sigma tension with local atomic clock bounds. Future measurements by ESPRESSO and ELT-HIRES will provide a definitive test of these models., Comment: 8 pages, 12 figures, 3 tables, REVTEX 4-1

We present measurements of absorption by the 21cm hyperfine transition of neutral hydrogen toward radio sources at substantial look-back times. These data are used in combination with observations of rotational transitions of common interstellar molecules, to set limits on the evolution of the fine structure constant: (dot alpha)/alpha < 3.5e-15/yr to a look-back time of 4.8 Gyr. The neutral hydrogen observations employed Very Long Baseline Interferometry in order to mitigate the substantial uncertainty arising from the fact that observations at very different wavelengths may probe different lines-of-site due to frequency dependent structure of the background source. We discuss the implication of these results on theories unifying natural forces based on compact quantum dimensions. In the context of string theory, the limit on the secular evolution of the scale factor of these compact dimensions, R, is (dot R)/R < 1e-15/yr. Including terrestrial and other astronomical measurements places limits (2sigma) on slow oscillations of R from the present to the epoch of cosmic nucleosynthesis, just seconds after the big bang, of (Delta R)/R < 1e-5., Physical Review Letters 85, 2511, fixed typo. fixed typo 2

Using Doppler-tuned fast-beam laser spectroscopy with co- and counterpropagating beams we have measured the three hyperfine components of the $1s2p^{3}P_{2}\ensuremath{-}^{3}P_{1}$ fine structure interval in ${}^{19}{\mathrm{F}}^{7+}$. Our result for the centroid is $957.6679(10){\mathrm{cm}}^{\ensuremath{-}1}$. Allowing for the hyperfine interaction the ``pure'' fine structure interval is determined to be $957.8730(12){\mathrm{cm}}^{\ensuremath{-}1}$. This result tests $O({\ensuremath{\alpha}}^{7}{m}_{e}{c}^{2})$ quantum electrodynamic corrections to high precision calculations which will be used to obtain a new value for the fine structure constant from the fine structure of helium.

We have measured the absolute optical frequency of the cesium ${D}_{1}$ line at 335 THz (895 nm). This frequency provides an important link for a new determination of the fine structure constant $\ensuremath{\alpha}$. The ${D}_{1}$ line has been compared with the fourth harmonic of a methane stabilized He-Ne laser at 88.4 THz ( $3.39\ensuremath{\mu}\mathrm{m}$). To measure the frequency mismatch of 18.39 THz between $4\ifmmode\times\else\texttimes\fi{}88.4\mathrm{THz}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}354\mathrm{THz}$ and the ${D}_{1}$ line a frequency comb spanning around 244 000 modes of a Kerr-lens mode-locked laser was used. We find 1 167 688 (81) kHz for the hyperfine splitting of the ${6P}_{1/2}$ state and 335 116 048 807 (41) kHz for the hyperfine centroid from which we derive ${\ensuremath{\alpha}}^{\ensuremath{-}1}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}137.0359924(41)$.

The properties of the ground state of the muonic helium atom $e\ensuremath{\mu}{}^{3}{\mathrm{He}}^{2+}$ have been calculated nonvariationally, using the correlation function hyperspherical harmonic method utilizing a nonlinear parametrization of the correlation function. The parametrization is similar to the one used in an earlier paper for $e\ensuremath{\mu}{}^{4}{\mathrm{He}}^{2+}$ but the differences in the convergence were found to be important for the choice of optimal parameters. The parametrization is especially suited to accelerate the convergence of singular operators. As a result, the obtained expectation values of the $\ensuremath{\delta}({\mathbf{r}}_{k})$ operators have error margins smaller than the differences in the literature. The lowest-order hyperfine splitting, which depends on the fine structure constant and on the magnetic moment of the ${}^{3}{\mathrm{He}}^{2+}$ nucleus, is compared with values in the literature.

The fine structure interval of P states in hydrogenlike systems can be determined theoretically with high precision, because the energy levels of P states are only slightly influenced by the structure of the nucleus. Therefore a measurement of the fine structure may serve as an excellent test of QED in bound systems or alternatively as a means of determining the fine structure constant $\alpha$ with very high precision. In this paper an improved analytic calculation of higher-order binding corrections to the one-loop self energy of 3P and 4P states in hydrogen-like systems with low nuclear charge number $Z$ is presented. A comparison of the analytic results to the extrapolated numerical data for high $Z$ ions serves as an independent test of the analytic evaluation. New theoretical values for the Lamb shift of the P states and for the fine structure splittings are given.

We report on the spectroscopy of radio-frequency transitions between nearly-degenerate, opposite-parity excited states in atomic dysprosium (Dy). Theoretical calculations predict that these states are very sensitive to variation of the fine-structure constant, $\alpha$, owing to large relativistic corrections of opposite sign for the opposite-parity levels. The near degeneracy reduces the relative precision necessary to place constraints on variation of $\alpha$ competitive with results obtained from the best atomic clocks in the world. Additionally, the existence of several abundant isotopes of Dy allows isotopic comparisons that suppress common-mode systematic errors. The frequencies of the 754-MHz transition in $^{164}$Dy and 235-MHz transition in $^{162}$Dy were measured over the span of two years. Linear variation of $\alpha$ is found to be $\dot{\alpha}/\alpha = (-5.8\pm6.9)\times10^{-17}$ yr$^{-1}$, consistent with zero. The same data are used to constrain the dimensionless parameter $k_\alpha$, characterizing a possible coupling of $\alpha$ to a changing gravitational potential. We find that $k_\alpha = (-5.5\pm5.2)\times10^{-7}$, essentially consistent with zero and the best constraint to date., Comment: 5 pages, 3 figures

We propose a new method to probe for variations in the fine structure constant alpha using clusters of galaxies, opening up a window on a new redshift range for such constraints. Hot clusters shine in the X-ray mainly due to bremsstrahlung, while they leave an imprint on the CMB frequency spectrum through the Sunyaev-Zel'dovich effect. These two physical processes can be characterized by the integrated Comptonization parameter Y_SZ DA^2 and its X-ray counterpart, the Y_X parameter. The ratio of these two quantities is expected to be constant from numerical simulations and current observations. We show that this fact can be exploited to constrain alpha, as the ratio of the two parameters depends on the fine structure constant as alpha^{3.5}. We determine current constraints from a combination of Planck SZ and XMM-Newton data, testing different models of variation of alpha. When fitting for a constant value of alpha, we find that current constraints are at the 1% level, comparable with current CMB constraints. We discuss strategies for further improving these constraints by almost an order of magnitude., Comment: 7 pages, 3 figures

Electronic screening renormalizes the linear bands of graphene and in the vicinity of the Dirac point, creates a diamond shaped structure in the quasiparticle spectral density. This is a result of electron-plasmon scattering processes which produce a finite momentum feature referred to as the `plasmaron ring'. In this work we explore the effects of uniaxial strain on these spectral features with the aim of understanding how strain modifies correlations. We derive and calculate the spectral density to the G$_0$W-RPA level which allows us to identify the dispersive behaviour of the diamond geometry, and thus electron-plasmon scattering, for variation in electron-electron coupling strength and magnitude of applied strain. We find that the application of strain changes the geometry (in momentum) of the electron-plasmon scattering and that renormalizations beyond simple geometrical scalings further enhance this effect. These results suggest that the properties of the plasmaron ring can be tuned through the application of uniaxial strain, effectively producing a larger fine structure constant without the need to change the sample substrate., Comment: 7 pages, 4 figures

In polyatomic molecules with \Pi\ 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 \Sigma+ 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., Comment: 10 pages, RevTeX; v2: one figure added and hyperfine structure included

To a first approximation, a single photon incident upon an ideal beam splitter will either be transmitted or reflected. The author has recently shown, however, that an ideal beam splitter has a small probability of coherently splitting a single photon into a pair of secondary photons, conserving energy in the process. This process is analogous to parametric down-conversionl,2, except that the necessary nonlinearity does not come from any inherent nonlinearity of the medium but comes, instead, from the A 2 term in the Hamiltonian. The necessary inversion asymmetry is also not a property of the medium and is dependent upon the direction of the wave vectors of the incident and secondary photons. The secondary photons have little or no first-order coherence but they do possess second-order coherence, which allows their use in two-photon interferometry3.

Highly accurate numerical evaluation of the sixth-order term of the electron anomalous magnetic moment {ital a}{sub {ital e}} has detected an error in the analytic value of a fourth-order infrared-divergent integral, which is needed to obtain the best estimate of the {alpha}{sup 3} term as a combination of analytic values of 67 Feynman diagrams and numerical values of 5 diagrams for which no analytic results are known. Correction of this error leads to a small but significant revision of the {alpha}{sup 3} term. As a consequence the fine structure constant {alpha} determined from theory and experiment of {ital a}{sub {ital e}} is reduced by 55{times}10{sup {minus}9}. {copyright} {ital 1995 The American Physical Society.}

We describe a new test for possible variations of the fine structure constant alpha by comparisons of rates between clocks based on hyperfine transitions in alkali atoms with different atomic number Z. H-maser, Cs, and Hg(+) clocks have a different dependence on alpha via relativistic contributions of order (Z-alpha)(sup 2). Recent H-maser vs Hg(+) clock comparison data improve laboratory limits on a time variation by 100-fold to give dot-alpha less than or equal to 3.7 x 10(exp -14)/yr. Future laser cooled clocks (Be(+), Rb, Cs, Hg(+), etc.), when compared, will yield the most sensitive of all tests for dot-alpha/alpha.

We study ultranarrow $5{s}_{1/2}$-$4{f}_{5/2}$ transitions in Nd${}^{13+}$ and Sm${}^{15+}$ and demonstrate that they lie in the optical region. The transitions are insensitive to external perturbations. At the same time they are sensitive to the variation of the fine structure constant $\ensuremath{\alpha}$. The fractional accuracy of the frequency of the transitions can be smaller than ${10}^{\ensuremath{-}19}$, which may provide a basis for atomic clocks of superb accuracy. Sensitivity to the variation of $\ensuremath{\alpha}$ approaches ${10}^{\ensuremath{-}20}$ per year.

The recoil, vacuum polarization and electron vertex corrections of first and second orders in the fine structure constant $\alpha$ and the ratio of electron to muon and electron to \alpha-particle masses are calculated in the hyperfine splitting of the $1s^{(e)}_{1/2}2s^{(\mu)}_{1/2}$ state of muonic helium atom (\mu e ^4_2He) on the basis of a perturbation theory. We obtain total result for the muonically excited state hyperfine splitting $\Delta \nu^{hfs}=4295.66$ MHz which improves previous calculations due to the account of new corrections and more accurate treatment of the electron vertex contribution.

Recent years have seen a renewed interest in the Oklo phenomenon, particularly in relation to the study of time variation of the fine structure constant. The neutron fluence is one of the crucial parameters for Oklo reactors. Several approaches to its determination were elaborated in the past. We consider whether it possible to use the present isotopic La138/139 data for RZ10 as an additional indicator of neutron fluences in the active cores of the reactors. We calculate the dependence of the Oklo La138 abundance on neutron fluence and elemental lanthanum concentration. The neutron fluence in RZ10 can be deduced from lanthanum isotopic data, but requires reliable data on the primordial elemental abundance. Conversely, if the fluence is known, the isotope ratio provides information on the primordial lanthanum abundance that is not otherwise easily determined., Comment: 4 pages, 2 figures

We study electronic transitions in highly charged Cf ions that are within the frequency range of optical lasers and have very high sensitivity to potential variations in the fine-structure constant, $\ensuremath{\alpha}$. The transitions are in the optical range despite the large ionization energies because they lie on the level crossing of the $5f$ and $6p$ valence orbitals in the thallium isoelectronic sequence. ${\mathrm{Cf}}^{16+}$ is a particularly rich ion, having several narrow lines with properties that minimize certain systematic effects. ${\mathrm{Cf}}^{16+}$ has very large nuclear charge and large ionization energy, resulting in the largest $\ensuremath{\alpha}$ sensitivity seen in atomic systems. The lines include positive and negative shifters.