Search

We use astrophysical and atomic clock tests of the stability of the fine-structure constant a, together with type la supernova and Hubble parameter data, 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 ζ to the electromagnetic sector) the a variation. We show how current data tightly constrain a combination of ζ and the dark energy equation of state w0. At the 95% confidence level and marginalizing over w0 we find |ζ| < 5 × 10-6, with the atomic clock tests dominating the constraints. The forthcoming generation of high-resolution ultrastable spectrographs will enable significantly tighter constraints. [ABSTRACT FROM AUTHOR]

Astrophysical tests of the stability of dimensionless fundamental couplings, such as the fine-structure constant α, 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 a 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. [ABSTRACT FROM AUTHOR]

Models of modified gravity, whereby local tests of gravity are evaded thanks to a screening mechanism of the chameleon or Damour-Polyakov types, lead to a spatial variation of the particle masses and the fine structure constant. This is triggered by the environmental dependence of the value of the scalar field whose presence modifies gravity. In dense media, the field settles at a density dependent value while in sparse environments it takes the background cosmological value. We estimate that the maximal deviation of constants from their present values is constrained by local tests of gravity, and must be less than 10-6. [ABSTRACT FROM AUTHOR]

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 that also couples to the electromagnetic sector of the theory, obtain the corresponding behavior of the finestructure constant a 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 a, thus constraining this putative coupling to electromagnetism. We find that values of the coupling that would provide a good fit to spectroscopic measurements of a 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. [ABSTRACT FROM AUTHOR]

We test the consistency of several independent astrophysical measurements of fundamental dimension-less constants. In particular, we compare direct measurements of the fine-structure constant a and the proton-to-electron mass ratio p = mp/me (mostly in the optical/ultraviolet) with combined measurements of a, p, and the proton gyromagnetic ratio gp (mostly in the radio band). We point out some apparent inconsistencies, which suggest that hidden systematics may be affecting some of the measurements. These findings demonstrate the importance of future, more precise measurements with ALMA, ESPRESSO, and ELT-HIRES. We also highlight some of the implications of the currently available measurements for fundamental physics, specifically for unification scenarios. [ABSTRACT FROM AUTHOR]

There have been recent reports of unexpectedly large velocity dipole in the NRAO VLA Sky Survey (NVSS) data. We investigate whether the excess in the NVSS dipole reported can be of cosmological origin. We assume a long wavelength inhomogeneous scalar perturbation of the form a sin(>cz) and study its effects on the matter density contrasts. Assuming an ideal fluid model, we calculate, in the linear regime, the contribution of the inhomogeneous mode to the density contrast. We calculate the expected dipole in the large scale structure (LSS) for two cases, first assuming that the mode is still superhorizon everywhere, and second assuming the mode is subhorizon but has crossed the horizon deep in matter domination and is subhorizon everywhere in the region of the survey (NVSS). In both cases, we find that such an inhomogeneous scalar perturbation is sufficient to generate the reported values of dipole anisotropy in LSS. For the superhorizon modes, we find values which are consistent with both cosmic microwave background and NVSS results. We also predict signatures for the model which can be tested by future observations. [ABSTRACT FROM AUTHOR]

We propose a new method to probe for variations in the fine structure constant a 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 cosmic microwave background (CMB) frequency spectrum through the Sunyaev-Zel'dovich effect. These two physical processes can be characterized by the integrated Comptonization parameter YSZD2A and its x-ray counterpart, the Yx 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 a, as the ratio of the two parameters depends on the fine structure constant as ∝ α3,5. We determine current constraints from a combination of Planck SZ and XMM-Newton data, testing different models of variation of a. When fitting for a constant value of α, we find that current constraints are at the 0.8% level, comparable with current CMB bounds. We discuss strategies for further improving these constraints by at least a factor ~3. [ABSTRACT FROM AUTHOR]

The angular power spectrum of the cosmic microwave background temperature anisotropies is a good probe for looking into the primordial density fluctuations at large scales in the Universe. Here we reexamine the angular power spectrum of the Wilkinson Microwave Anisotropy Probe data, paying particular attention to the fine structures (oscillations) at ℓ = 100-150 reported by several authors. Using Monte Carlo simulations, we confirm that the gap from the simple power law spectrum is a rare event, about 2.5-3σ-, if these fine structures are generated by experimental noise and cosmic variance. Next, in order to investigate the origin of the structures, we examine frequency and direction dependences of the fine structures by dividing the observed QUV frequency maps into four sky regions. We find that the structures around e 120 do not have significant dependences either on frequencies or direction. For the structure around σ 140, however, we find that the characteristic signature found in the all-sky power spectrum is attributed to the anomaly only in the southeast region. [ABSTRACT FROM AUTHOR]

We present a detailed analysis (including redshift tomography) of the cosmic dipoles in the Keck + VLT quasar absorber and in the Union2 Snia samples. We show that the fine structure constant cosmic dipole obtained through the Keck + VLT quasar absorber sample at 4.1 σ level is anomalously aligned with the corresponding dark energy dipole obtained through the Union2 sample at 2σ level. The angular separation between the two dipole directions is 11.3° ± 11.8°. We use Monte Carlo simulations to find the probability of obtaining the observed dipole magnitudes with the observed alignment, in the context of an isotropic cosmological model with no correlation between dark energy and fine structure constant α. We find that this probability is less than one part in 106. We propose a simple physical model (extended topological quintessence) which naturally predicts a spherical inhomogeneous distribution for both dark energy density and fine structure constant values. The model is based on the existence of a recently formed giant global monopole with Hubble scale core which also couples nonminimally to electromagnetism. Aligned dipole anisotropics would naturally emerge for an off-center observer for both the fine structure constant and for dark energy density. This model smoothly reduces to ACDM for proper limits of its parameters. Two predictions of this model are (a) a correlation between the existence of strong cosmic electromagnetic fields and the value of α and (b) the existence of a dark flow on Hubble scales due to the repulsive gravity of the global defect core ("Great Repulser") aligned with the dark energy and a dipoles. The direction of the dark flow is predicted to be towards the spatial region of lower accelerating expansion. Existing data about the dark flow are consistent with this prediction. [ABSTRACT FROM AUTHOR]

We forecast the ability of future cosmic microwave background and galaxy lensing surveys to constrain variations of the fine structure constant. We found that lensing data, as those expected from satellite experiments as Euclid could improve the constraint from future cosmic microwave background experiments leading to a Δ&agr;/&agr; = 8 × 10-4 accuracy. A variation of the fine structure constant &agr; is strongly degenerate with the Hubble constant H0 and with inflationary parameters as the scalar spectral index ns. These degeneracies may cause significant biases in the determination of cosmological parameters if a variation in &agr; as large as ∼0.5% is present at the epoch of recombination. [ABSTRACT FROM AUTHOR]

For a complete development of quantum electrodynamics in the presence of a strong external field, proper understanding of the resonant processes and all their peculiarities is essential. We present our attempt to analytically investigate the resonant case of laser-assisted ultrarelativistic electron-positron pair photoproduction on a nucleus. The initial gamma quantum with energy ℏωi≲100  GeV and external field with intensity up to I∼1024 W/cm² are considered. Due to the presence of the external field, the intermediate virtual particle may become real, herewith the second order process in the fine structure constant effectively reduces into the two successive first order processes. All inherent kinematics features were discussed in details and the resonant differential cross sections with simultaneous registration of the produced particle (positron for channel A or electron for channel B) energy and its outgoing angle were obtained. We established that the resonant energies of produced particles acquire two different values with respect to the positron (channel A) or electron (channel B) outgoing angle. Additionally, the certain minimal amount of absorbed wave photons is required for resonance to happen. Wherein, the resonant differential cross section significantly exceeds the corresponding one without the external field within the particular kinematic regions. Consequently, the considered process can be used as a marker for probing theoretical predictions of quantum electrodynamics with strong background electromagnetic field. [ABSTRACT FROM AUTHOR]

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 Z N exchange symmetry that relates the Standard Model to several copies of 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. [ABSTRACT FROM AUTHOR]

Einstein equivalence principle (EEP), as one of the foundations of general relativity, is a fundamental test of gravity theories. In this paper, we propose a new method to test the EEP of electromagnetic interactions through observations of black hole photon rings, which naturally extends the scale of Newtonian and post-Newtonian gravity where the EEP violation through a variable fine structure constant has been well constrained to that of stronger gravity. We start from a general form of Lagrangian that violates EEP, where a specific EEP violation model could be regarded as one of the cases of this Lagrangian. Within the geometrical optical approximation, we find that the dispersion relation of photons is modified: for photons moving in circular orbit, the dispersion relation simplifies, and behaves such that photons with different linear polarizations perceive different gravitational potentials. This makes the size of black hole photon ring depend on polarization. Further assuming that the EEP violation is small, we derive an approximate analytic expression for spherical black holes showing that the change in size of the photon ring is proportional to the violation parameters. We also discuss several cases of this analytic expression for specific models. Finally, we explore the effects of black hole rotation and derive a modified proportionality relation between the change in size of photon ring and the violation parameters. The numerical and analytic results show that the influence of black hole rotation on the constraints of EEP violation is relatively weak for small magnitude of EEP violation and small rotation speed of black holes. [ABSTRACT FROM AUTHOR]

The recently improved observation of the fine structure constant has led to a negative 2.4σ anomaly of electron g-2. Combined with the long-existing positive 4.2σ 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 by the Higgsino-sneutrino contributions to (g-2)e and (g-2)μ. The spectrum features prefer light μ, which can predict mZ naturally, and it is not difficult to obtain a τ-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 constraints. [ABSTRACT FROM AUTHOR]

The baryon acoustic oscillations (BAO) have proven to be an invaluable tool in constraining the expansion history of the Universe at late times and are characterized by the comoving sound horizon at the baryon drag epoch rs(zd). The latter quantity can be calculated either numerically using recombination codes or via fitting functions, such as the one by Eisenstein and Hu, made via grids of parameters of the recombination history. Here we quantify the accuracy of these expressions and show that they can strongly bias the derived constraints on the cosmological parameters using BAO data. Then, using a machine learning approach, called the genetic algorithms, we proceed to derive new analytic expressions for rs(zd), which are accurate at the ∼0.003% level in a range of 10σ around the Planck 2018 best fit or ∼0.018% in a much broader range, compared to ∼2-4% for the Eisenstein and Hu expression, thus obtaining an improvement of two to three orders of magnitude. Moreover, we also provide fits that include the effects of massive neutrinos and an extension to the concordance cosmological model assuming variations of the fine structure constant. Finally, we note that our expressions can be used to ease the computational cost required to compute rs(zd) with a Boltzmann code when deriving cosmological constraints using BAO data from current and upcoming surveys. [ABSTRACT FROM AUTHOR]

In the framework of the Standard Model (SM) a theoretical description of the neutron beta decay is given at the level of 10-5. The neutron lifetime and correlation coefficients of the neutron beta decay for a polarized neutron, a polarized electron, and an unpolarized proton are calculated at the account for (i) the radiative corrections (RC) of order O(αEe/mN)∼10-5, i.e., O(αEe/mN) RC, to Sirlin's outer and inner O(α/π) RC, where α and Ee are the fine-structure constant and the electron energy, respectively; (ii) the outer O(αEe/mN) RC, caused by Sirlin's outer O(α/π) RC and the phase-volume of the neutron beta decay, calculated to next-to-leading order in the large nucleon mass mN expansion; (iii) the corrections of order O(Ee²/mN²)∼10-5, caused by weak magnetism and proton recoil; and (iv) Wilkinson's corrections of order 10-5 [Wilkinson, Nucl. Phys. A377, 474 (1982)]. These corrections define the SM background of the theoretical description of the neutron beta decay at the level of 10-5, which is required by experimental searches of interactions beyond the SM with experimental uncertainties of a few parts of 10-5. [ABSTRACT FROM AUTHOR]

We investigate the contributions of the hadronic structure of the neutron to radiative O(αEe/mN) corrections [or the inner O(αEe/mN) RC] to the neutron beta decay, where α, Ee, and mN are the fine-structure constant, the electron energy, and the nucleon mass, respectively. We perform the calculation within the effective quantum field theory of strong low-energy pion-nucleon interactions described by the linear σ model with chiral SU(2)×SU(2) symmetry and electroweak hadron-hadron, hadron-lepton, and lepton-lepton interactions for the electron-lepton family with SU(2)L×U(1)Y symmetry of the standard electroweak theory [Ivanov et al., Phys. Rev. D 99, 093006 (2019)]. We show that after renormalization, carried out in accordance with Sirlin's prescription [Sirlin, Phys. Rev. 164, 1767 (1967)], the inner O(αEe/mN) RC are of the order of a few parts of 10-5-10-4. This agrees well with the results obtained in [Ivanov et al., Phys. Rev. D 99, 093006 (2019)]. [ABSTRACT FROM AUTHOR]

We examine the constraints on sub-GeV dark sector particles set by the proto-neutron star cooling associated with the core-collapse supernova event SN1987a. Considering explicitly a dark photon portal dark sector model, we compute the relevant interaction rates of dark photon (A′) and dark fermion (χ) with the Standard Model particles as well as their self-interaction inside the dark sector. We find that even with a small dark sector fine structure constant αD≪1, dark sector self-interactions can easily lead to their own self-trapping. This effect strongly limits the energy luminosity carried away by dark sector particles from the supernova core and thus drastically affects the parameter space that can be constrained by SN1987a. We consider specifically two mass ratios mA′=3mχ and 3mA′=mχ which represent scenarios where the decay of A′ to χχ is allowed or not. For mA′=3mχ, we show that this effect can completely evade the supernova bounds on widely examined dark photon parameter space for a dark sector with αD≳10-7. In particular, for the mass range mχ≲20 MeV, supernova bounds can only be applied to weakly self-interacting dark sector with αD≲10-15. For 3mA′=mχ, bounds in regions where αD≳10-7 for mχ≲20 MeV can be evaded similarly. Our findings thus imply that the existing supernova bounds on light dark particles can be generally eluded by a similar self-trapping mechanism. This also implies that nonstandard strongly self-interacting neutrino is not consistent with the SN1987a observation. Same effects can also take place for other known stellar bounds on dark sector particles. [ABSTRACT FROM AUTHOR]

We show that the one-loop Euler-Heisenberg QED effective Lagrangian in a constant background field acquires a very different nonperturbative trans-series structure at two-loop and higher-loop order in the fine structure constant. Beyond one-loop, virtual particles interact, causing fluctuations about the instantons, whereby the simple poles of the one-loop Borel transform become branch points. We illustrate this in detail at two-loop order using Ritus's seminal result for the renormalized two-loop effective Lagrangian as an exact double-integral representation, and propose a possible new approach to computations at higher loop order. Our methods yield remarkably accurate extrapolations from weak-field to strong-field, and from magnetic to electric background field, at both one-loop and two-loop order, based on surprisingly little perturbative input. [ABSTRACT FROM AUTHOR]

We propose a simple model based on the assumption that the varying fine structure constant α is an effect of the cosmological expansion to investigate the relation between the varying α 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 α 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. [ABSTRACT FROM AUTHOR]

Investigation of quasibound states of black holes is significant for expected ultralight particles, as well as black holes through gravitational waves. We first investigate quasibound states of a massive scalar field for dilatonic charged black holes via numerical analysis. We study the complex eigenfrequencies of the massive scalar field in a wide range of gravitational fine structure constant µM in detail, and show the effects of charge. Further, we study the eigenfrequencies of the massive field through an analytical approach by matching the near horizon solution and far field solution, and find its spectra for excited states by the iteration method. We demonstrate that the numerical solution and analytical solution perfectly agree with each other in the region where charge of the black hole is large, both for real and imaginary parts of the eigenfrequencies. [ABSTRACT FROM AUTHOR]

We study the cosmological consequences of a class of Dirac-Born-Infeld models, and assess their viability as a candidate for the recent acceleration of the Universe. The model includes both the rolling tachyon field and the generalized Chaplygin gas models as particular limits, and phenomenologically each of these provides a possible mechanism for a deviation of the value of the dark energy equation of state from its canonical (cosmological constant) value. The field-dependent potential that is characteristic of the rolling tachyon also leads to variations of the fine-structure constant a, implying that the model can be constrained both by standard cosmological probes and by astrophysical measurements of a. Our analysis, using the latest available low-redshfit data and local constraints from atomic clock and weak equivalence principle experiments, shows that the two possible deviations of the dark energy equation of state are constrained to be log 10 (1 + w 0) V < - 7.85 and log 10 (1 + w 0) C < - 0.85, respectively for the rolling tachyon and Chaplygin components, both being at the 95.4% confidence level (although the latter depends on the choice of priors, in a way that we quantify). Alternatively, the 95.4% confidence level bound on the dimensionless slope of the potential is log 10 < - 5.36. This confirms previous analyses indicating that in these models the potential needs to be extremely flat. [ABSTRACT FROM AUTHOR]

Scattering processes in laser backgrounds are degenerate to the emission of unobservable photons collinear with the laser. We identify processes and observables for which such degeneracies factorize and exponentiate, obtaining the leading-order intensity dependence of these inclusive observables at high laser intensity, correct to all orders in the fine-structure constant (all loops, all emissions). The results show an exponential intensity dependence distinct from that predicted by the Narozhny-Ritus conjecture on the high-intensity behavior of quantum electrodynamics in strong fields. [ABSTRACT FROM AUTHOR]

We calculate the rate of collisional decay of the axial charge in an ultrarelativistic electron-positron plasma, also known as the chirality flipping rate. We find that contrary to the existing estimates, the chirality flipping rate appears already in the first order in the fine-structure constant α and is therefore orders of magnitude greater than previously believed. The main channels for the rapid relaxation of the axial charge are the collinear emission of a weakly damped photon and the Compton scattering. The latter contributes to the O(α) result because of the infrared divergence in its cross section, which is regularized on the soft scale ∼eT due to the thermal corrections. Our results are important for the description of the early Universe processes (such as leptogenesis or magnetogenesis) that affect differently left- and right-chiral fermions of the Standard Model, as discussed in more details in the companion Letter. [ABSTRACT FROM AUTHOR]

We derive an electrically charged static black hole spacetime of the Einstein-Euler-Heisenberg theory, in terms of the Plebański dual variables. This solution is a nonlinear electromagnetic generalization of the Reissner-Nordström 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 a. We study all possible equatorial trajectories of test particles. Moreover, the orbits of photons are analyzed by means of the effective Plebański 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. [ABSTRACT FROM AUTHOR]

Scalars that carry lepton number can help mediate would-be lepton number-violating processes, such as neutrinoless double β decay or lepton scattering-mediated nucleon-antinucleon conversion. Here, we show that such new scalars can also solve the anomaly in precision determinations of the fine-structure constant α from atom interferometry and from the electron's anomalous magnetic moment, ae≡(g-2)e/2, by reducing |ae|. Study of the phenomenological constraints on these solutions favor a doubly charged scalar with mass below the GeV scale. Significant constraints arise from the measurement of the parity-violating asymmetry in Møller scattering, and we consider the implications of the next-generation MOLLER experiment at Jefferson Laboratory and of an improved ae measurement. [ABSTRACT FROM AUTHOR]

We address the issue of radiative corrections to Kaluza-Klein (KK) masses in five-dimensional quantum electrodynamics (QED) supplemented by aether Lorentz-violating terms. Specifically, we compute the corrections to the Kaluza-Klein (KK) photon masses from one fermion loop. In general, the KK masses receive radiative corrections due to breaking the five-dimensional Lorentz invariance by compactification. As we show, the presence of the additional Lorentz violating factor, an aether background, leads to the nontrivial modification of these corrections. This model may be of interest in addressing important phenomenological issues such as the relation between radiative corrected KK mass splitting of a particular mode and uncertainties in the measurements and/or possible spatial variation of the fine-structure constant. For the recent data on the fine-structure constant, we find a KK mass splitting of magnitude ~0.01 MeV for the first excited Kaluza-Klein gauge boson at TeV scale. On the other hand, the large KK modes limit displays a very interesting phenomenon, showing the very special role of the aether in protecting the higher modes from the quantum corrections. [ABSTRACT FROM AUTHOR]

One of the clear predictions of string theory is the presence of a dynamical scalar partner of the spin-2 graviton, known as the dilaton. This will violate the Einstein equivalence principle, leading to a plethora of possibly observable consequences which in a cosmological context include dynamical dark energy and spacetime variations of nature's fundamental constants. The runaway dilaton scenario of Damour, Piazza, and Veneziano is a particularly interesting class of string theory inspired models which can in principle reconcile a massless dilaton with experimental data. Here we use the latest background cosmology observations, astrophysical and laboratory tests of the stability of the fine-structure constant, and local tests of the weak equivalence principle to provide updated constraints on this scenario, under various simplifying assumptions. Overall we find consistency with the standard ΛCDM paradigm. We improve the existing constraints on the coupling of the dilaton to baryonic matter by a factor of 6 and to the dark sector by a factor of 2. At the one-sigma level the current data already exclude dark sector couplings of order unity, which would be their natural value. [ABSTRACT FROM AUTHOR]

The most recent measurement of the fine structure constant leads to a 2.4σ deviation in the electron anomalous magnetic moment ge-2, while the muon anomalous magnetic moment gμ-2 has a long-standing 3.7σ deviation in the opposite direction. We show that these deviations can be explained in a three-loop neutrino mass model based on an E6 Grand Unified Theory. We also study the impact such a model can have on the anomalous events observed by the ANITA experiment and find an insufficient enhancement of the event rate. [ABSTRACT FROM AUTHOR]

We present next-to-next-to leading order (NNLO) quantum electrodynamics (QED) corrections to the production of the Higgs boson in bottom quark annihilation at the Large Hadron Collider (LHC) in the five flavor scheme. We have systematically included the NNLO corrections resulting from the interference of quantum chromodynamics (QCD) and QED interactions. We have investigated the infrared (IR) structure of the bottom quark form factor up to two-loop level in QED and in QCD×QED using K+G equation. We find that the IR poles in the form factor are controlled by the universal cusp, collinear and soft anomalous dimensions. In addition, we derive the QED as well as QCD×QED contributions to soft distribution function as well as to the ultraviolet renormalization constant of the bottom Yukawa coupling up to second order in strong coupling and fine structure constant. Finally, we report our findings on the numerical impact of the NNLO results from QED and QCD×QED at the LHC energies taking into account the dominant NNLO QCD corrections. [ABSTRACT FROM AUTHOR]

This paper describes a computation of a part of the QED contribution to the electron anomalous magnetic moment that was performed by the author with the help of a supercomputer. The computed part includes all 5-loop QED Feynman graphs without lepton loops. The calculation has led to the result A1(10)[no lepton loops]=6.793(90) that is slightly different than the value 7.668(159) presented by T. Aoyama, T. Kinoshita, and M. Nio in 2018. The discrepancy is about 4.8σ. The computation gives the first independent check for that value. A shift in the fine-structure constant prediction is revealed in the paper. The developed calculation method is based on (a) a subtraction procedure for removing all ultraviolet and infrared divergences in Feynman parametric space before integration; (b) a nonadaptive Monte Carlo integration that uses the probability density functions that are constructed for each Feynman graph individually using its combinatorial structure. The method is described briefly in the paper (with the corresponding references to the previous papers). The values for the contributions of nine gauge-invariant classes splitting the whole set are presented in the paper. Moreover, the whole set of all 5-loop graphs without lepton loops is split into 807 subsets for comparison (in the future) of the calculated values with the values obtained by other methods. These detailed results are presented in the supplemental materials. Also, the supplemental materials contain the contribution values for each of 3213 individual Feynman graphs. An "oscillating" nature of these values is discussed. A realization of the numerical integration on the graphics accelerator NVidia Tesla V100 (as a part of the supercomputer "Govorun" from JINR, Dubna) is described with technical details such as pseudorandom generators, calculation speed, code sizes and structure, prevention of round-off errors and overflows, etc. [ABSTRACT FROM AUTHOR]

We investigate the effect of an applied constant and uniform magnetic field in the fine-structure constant of massive and massless QED. In massive QED, it is shown that a strong magnetic field removes the so called Landau pole and that the fine-structure constant becomes anisotropic having different values along and transverse to the field direction. Contrary to other results in the literature, we find that the anisotropic fine-structure constant always decreases with the field. We also study the effect of the running of the coupling constant with the magnetic field on the electron mass. We find that in both cases of massive and massless QED, the electron dynamical mass always decreases with the magnetic field, what can be interpreted as an inverse magnetic catalysis effect. [ABSTRACT FROM AUTHOR]

We present an implementation and numerical study of the Standard Model couplings, masses, and vacuum expectation value (VEV), using the pure MS̄ renormalization scheme based on dimensional regularization. Here, the MS̄ Lagrangian parameters are treated as the fundamental inputs, and the VEV is defined as the minimum of the Landau gauge effective potential, so that tadpole diagrams vanish, resulting in improved convergence of perturbation theory. State-of-the-art calculations relating the MS̄ inputs to on-shell observables are implemented in a consistent way within a public computer code library, smdr (standard model in dimensional regularization), which can be run interactively or called by other programs. Included here for the first time are the full two-loop contributions to the Fermi constant within this scheme and studies of the minimization condition for the VEV at three-loop order with four-loop QCD effects. We also implement and study the scale dependence of all known multiloop contributions to the physical masses of the Higgs boson, the W and Z bosons, and the top quark, the fine structure constant and weak mixing angle, and the renormalization group equations and threshold matching relations for the gauge couplings, fermion masses, and Yukawa couplings. [ABSTRACT FROM AUTHOR]

We present an implementation and numerical study of the Standard Model couplings, masses, and vacuum expectation value (VEV), using the pure MS̄ renormalization scheme based on dimensional regularization. Here, the MS̄ Lagrangian parameters are treated as the fundamental inputs, and the VEV is defined as the minimum of the Landau gauge effective potential, so that tadpole diagrams vanish, resulting in improved convergence of perturbation theory. State-of-the-art calculations relating the MS̄ inputs to on-shell observables are implemented in a consistent way within a public computer code library, smdr (standard model in dimensional regularization), which can be run interactively or called by other programs. Included here for the first time are the full two-loop contributions to the Fermi constant within this scheme and studies of the minimization condition for the VEV at three-loop order with four-loop QCD effects. We also implement and study the scale dependence of all known multiloop contributions to the physical masses of the Higgs boson, the W and Z bosons, and the top quark, the fine structure constant and weak mixing angle, and the renormalization group equations and threshold matching relations for the gauge couplings, fermion masses, and Yukawa couplings. [ABSTRACT FROM AUTHOR]

We study an ultrarelativistic QED plasma in thermal equilibrium. Plasmons--photon collective excitations--are postulated to correspond not to poles of the retarded photon propagator but to poles of the propagator multiplied by the fine-structure constant. This product is an invariant of the renormalization group that is independent of an arbitrarily chosen renormalization scale. In addition, our proposal is physically motivated since one needs to scatter a charged particle off a plasma system to probe its spectrum of collective excitations. We present a detailed calculation of the QED running coupling constant at finite temperature using the Keldysh-Schwinger representation of the real-time formalism. We discuss the issue of how to choose the renormalization scale and show that the temperature is a natural choice which prevents the breakdown of perturbation theory through the generation of potentially large logarithmic terms. Our method could be applied to anisotropic systems where the choice of the renormalization scale is less clear, and could have important consequences for the study of collective modes. [ABSTRACT FROM AUTHOR]

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" α≡GμM/ℏc∼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 α≪1. Here we use black hole perturbation theory to compute instability rates and decay widths for generic values of α, and we show that this leads to much larger cloud depletion estimates when α≳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. [ABSTRACT FROM AUTHOR]

A recent improved determination of the fine structure constant, α=1/137.035999046(27), leads to a ~2.4σ negative discrepancy between the measured electron anomalous magnetic moment and the standard model prediction. That situation is to be compared with the muon anomalous magnetic moment where a positive ~3.7σ discrepancy has existed for some time. A single scalar solution to both anomalies is shown to be possible if the two-loop electron Barr-Zee diagrams dominate the scalar one-loop electron anomaly effect and the scalar couplings to the electron and two photons are relatively large. We also briefly discuss the implications of that scenario. [ABSTRACT FROM AUTHOR]

In this work, we analyze the spatial and time variation of the fine structure constant (α) upon the theoretical framework developed by Bekenstein (Phys. Rev. D 66, 123514 (2002)). We have computed the field ψ related to α at first order of the weak-field approximation and have also improved the estimation of the nuclear magnetic energy and, therefore, their contributions to the source term in the equation of motion of ψ. We obtained that the results are similar to the ones published in L. Kraiselburd and H. Vucetich, Int. J. Mod. Phys. E 20, 101 (2011) which were computed using the zero order of the approximation, showing that one can neglect the first order contribution to the variation of the fine structure constant. Through the comparison between our theoretical results and the observational data of the Eötvös-type experiments or the time variation of α over the cosmological time scale, we set constraints on the free parameter of the Bekenstein model, namely the Bekenstein length. [ABSTRACT FROM AUTHOR]

The numerical value of the fine-structure constant generally leads to small isospin-breaking effects due to electromagnetism in QCD. This smallness complicates determining isospin breaking from lattice QCD computations that include electromagnetism. One solution to this problem consists of performing computations using larger-than-physical values of the electric charge, and subsequently extrapolating (or interpolating) to the physical value of the fine-structure constant. Motivated by recent lattice QCD + QED computations of electromagnetic masses employing this setup, we consider finite-volume effects arising from the use of larger-than-physical electric charges. A modified power-counting scheme, which is based on treating the fine-structure constant as larger than its physical value, is explored. Results for perturbative QED corrections, however, are surprising. Within the framework of nonrelativistic QED, multiloop diagrams exhibit a momentum factorization property that produces exact cancellations. We determine that power-law finite-volume effects vanish at the leading two- and three-loop order, as well as the next-to-leading two-loop order. For larger-than-physical charges, we consequently expect no appreciable volume corrections beyond leading-order QED. [ABSTRACT FROM AUTHOR]

The reported spatial variation in the fine structure constant at high redshift, if physical, could be due to the presence of dilatonic domains, and one or more domain walls inside our horizon. An absorption spectrum of an object in a different domain from our own would be characterized by a different value of α. We show that while a single-wall solution is statically comparable to a dipole fit, and is a big improvement over a weighted mean (despite adding three parameters), a two-wall solution is a far better fit (despite adding three parameters over the single-wall solution). We derive a simple model accounting for the two domain wall solution. The goodness of these fits is, however, dependent on the extra random error which was argued to account for the large scatter in most of the data. When this error is omitted, all the above solutions are poor fits to the data. When included, the solutions that exhibit a spatial dependence agree with the data much more significantly than the standard model; however, the standard model itself is not a terrible fit to the data, having a p value of ~20%. [ABSTRACT FROM AUTHOR]