Search for solar hadronic axions produced by a bremsstrahlung-like process

We have searched for hadronic axions which may be produced in the Sun by a bremsstrahlung-like process, and observed in the HPGe detector by an axioelectric effect. A conservative upper limit on the hadronic axion mass of ma?334 eV$m_a?334\text{eV}$ at 95% C.L. is obtained. Our experimental approach is based on the axion–electron coupling and it does not include the axion–nucleon coupling, which suffers from the large uncertainties related to the estimation of the flavor-singlet axial-vector matrix element.     

Search for solar axions with mass around 1 eV using coherent conversion of axions into photons

A search for solar axions has been performed using an axion helioscope which is equipped with a 2.3-m long 4 T superconducting magnet, a gas container to hold dispersion-matching gas, PIN-photodiode X-ray detectors, and a telescope mount mechanism to track the sun. A mass region around ma=1 eV$m_a=1\text{eV}$ was newly explored. From the absence of any evidence, analysis sets a limit on axion–photon coupling constant to be g_aγγ<5.6–13.4×¹⁰⁻¹⁰ GeV⁻¹$g_{a\gamma \gamma }<5.6\text{–}13.4\times {10}^{\mathrm{-10}}{\text{GeV}}^{\mathrm{-1}}$ for the axion mass of 0.84<ma<1.00 eV$0.84<m_a<1.00\text{eV}$ at 95% confidence level. It is the first result to search for the axion in the g_aγγ–ma$g_{a\gamma \gamma }\text{–}{m}_a$ parameter region of the preferred axion models with a magnetic helioscope.     

Windows over a new low energy axion

We outline some general features of possible extensions of the Standard Model that include anomalous U(1)$U(1)$ gauge symmetries, a certain number of axions and their mixings with the CP-odd Higgs sector. As previously shown, after the mixing one of the axions becomes a physical pseudoscalar (the axi-Higgs) that can take the role of a modified QCD axion. It can be driven to be very light by the same non-perturbative effects that are held responsible for the solution of the strong CP-problem. At the same time the axi-Higgs has a sizeable gauge interaction, which is not allowed to the Peccei–Quinn axion, possibly explaining the PVLAS results. We point out that the Wess–Zumino term, typical of these models, can be both interpreted as an anomaly inflow from higher dimensional theories (second window) but also as a result of partial decoupling of an extra Higgs sector (and of a fermion) that leaves behind an effective anomalous Abelian theory (first window) in a broken Stückelberg phase. The possibility that the axi-Higgs can be heavy, of the order of the Higgs mass or larger, however, cannot be excluded. The potentialities for the discovery of this particle and of anomaly effects in the neutral current sector at the LHC are briefly discussed in the context of a superstring inspired model (second window), but with results that remain valid also if any of the two possibilities is realized in Nature.     

Phenomenological implications of S-duality symmetry

It is proposed that S-duality is a fundamental symmetry of nature which is spontaneously broken. Axion and dilaton are identified with the doublet of the S  -duality symmetry group SL(2,R)$\mathit{SL}(2,\mathbb{R})$. The symmetry is broken at a high scale corresponding to the experimentally estimated axion decay constant fχ$f_{\chi }$. The symmetry breaking mechanism is discussed in analogy with PCAC in pion physics. S-duality invariant interactions of fermions with axion and dilaton doublet are introduced. The symmetry breaking mechanism contributes negligibly small corrections to fermion masses in the QCD sector. Inspired by universality in string theory, the S-duality invariant interaction of the axion–dilaton doublet to QCD fermions is proposed to generalize to all fermions. Phenomenological consequences of this broken symmetry are explored.     

Dilaton field and cosmic wave propagation

We study the electromagnetic wave propagation in the joint dilaton field and axion field. Dilaton field induces amplification/attenuation in the propagation while axion field induces polarization rotation. The amplification/attenuation induced by dilaton is independent of the frequency (energy) and the polarization of electromagnetic waves (photons). From observations, the agreement with and the precise calibration of the cosmic microwave background (CMB) to blackbody radiation constrains the fractional change of dilaton |Δψ|/ψ$|\mathrm{\Delta }\psi |/\psi$ to less than about 8×10⁻⁴$8\times {10}^{-4}$ since the time of the last scattering surface of the CMB.     

Radiative processes as a condensation phenomenon and the physical meaning of deformed canonical structures

We study the radiative corrections of QED₃ from the dual point of view and show that this process is the exact dual to the Julia–Toulouse mechanism introduced by Quevedo and Trugenberger [F. Quevedo, C.A. Trugenberger, Nucl. Phys. B 501 (1997) 143] some years ago. We discuss the physics behind this mechanism that involves condensation of topological defects. It is shown that the dual Stuckelberg mechanism is responsible for the “rank-jump” phenomenon that transforms the scalar field (dual to Maxwell in this dimensionality) into the vectorial self-dual field. This phenomenon is studied using the ideas of noncommutative fields theory that examines possible deformations of the canonical structure of some well-known models in (2+1)D$(2+1)\mathrm{D}$. A deformation is constructed linking the massless scalar field theory with the self-dual theory. This is the exact dual of the known deformation connecting the Maxwell theory with the Maxwell–Chern–Simons theory. Duality, radiative corrections, the Julia–Toulouse mechanism and canonical deformations are then used to establish a web of relations between the mentioned theories and to propose a physical picture of the deformation procedure adopted.     

Fermionic extension of the scalar Born–Infeld equation and its relation to the supersymmetric Chaplygin gas

In this Letter, we present a fermionic extension of the scalar Born–Infeld equation, which has been derived from the Nambu–Goto superstring action in (2+1)$(2+1)$ dimensions through the Cartesian parameterization. It is demonstrated that in the relativistic limit where c→∞$c\to \infty$, the fermionic Born–Infeld model reduces to the supersymmetric Chaplygin gas model in one spatial dimension. However, the supersymmetry itself is not preserved.     

A BRST gauge-fixing procedure for Yang–Mills theory on sphere

A gauge-fixing procedure for the Yang–Mills theory on an n  -dimensional sphere (or a hypersphere) is discussed in a systematic manner. We claim that Adler's gauge-fixing condition used in massless Euclidean QED on a hypersphere is not conventional because of the presence of an extra free index, and hence is unfavorable for the gauge-fixing procedure based on the BRST invariance principle (or simply BRST gauge-fixing procedure). Choosing a suitable gauge condition, which is proved to be equivalent to a generalization of Adler's condition, we apply the BRST gauge-fixing procedure to the Yang–Mills theory on a hypersphere to obtain consistent results. Field equations for the Yang–Mills field and associated fields are derived in manifestly O(n+1)$\mathrm{O}(n+1)$ covariant or invariant forms. In the large radius limit, these equations reproduce the corresponding field equations defined on the n-dimensional flat space.     

Cosmology with light axions from technicolor

We consider cosmological consequences of the spontaneous breaking of a global symmetry that is anomalous under technicolor interactions, leading to the emergence of a light axion-like particle. Avoiding overclosure of the universe by such axions yields the upper bound fa?¹⁰¹⁰ GeV$f_a?{10}^{10}\text{GeV}$ on the symmetry breaking scale, corresponding to keV-scale axions. However, diffuse X-ray background data typically require larger values of fa$f_a$. The overclosure and X-ray bounds can be reconciled if the axion initial amplitude of oscillations Ai∼fa/10$A_i\sim f_a/10$. In this case, a viable axionic dark matter candidate with a mass in the 50–100 eV range emerges. The detection of this type of dark matter may pose a challenge.     

Noncommutative Dirac oscillator in an external magnetic field

We show that (2+1)$(2+1)$-dimensional noncommutative Dirac oscillator in an external magnetic field is mapped onto the same but with reduced angular frequency in absence of magnetic field. We construct the relativistic Landau levels by solving corresponding Dirac equation in (2+1)$(2+1)$-dimensional noncommutative phase space. All the Landau levels become independent of noncommutative parameter for a critical value of the magnetic field. Several other interesting features along with the relevance of such models in the study of atomic transitions in a radiation field have been discussed.     

The search for axions

The axion is a light pseudoscalar particle predicted to exist as a consequence of the Peccei–Quinn solution to the strong-CP problem. Its abundant production in the early Universe along with its stability and insignificant interaction cross-section make it a prime dark matter candidate. This report summarises the search for dark matter axions using resonant microwave cavities as well as searches for axions produced in the Sun and in the laboratory. All of these current experiments focus on the axion–photon interaction, as coherent axion–photon mixing in strong magnetic fields of large spatial extent can make up for the extraordinary weakness of the the coupling of axions to photons.     

Vortex properties of mesoscopic superconducting samples

In this work we investigated theoretically the vortex properties of mesoscopic samples of different geometries, submitted to an external magnetic field. We use both London and Ginzburg–Landau theories and also solve the non-linear Time Dependent Ginzburg–Landau equations to obtain vortex configurations, equilibrium states and the spatial distribution of the superconducting electron density in a mesoscopic superconducting triangle and long prisms with square cross-section. For a mesoscopic triangle with the magnetic field applied perpendicularly to sample plane the vortex configurations were obtained by using Langevin dynamics simulations. In most of the configurations the vortices sit close to the corners, presenting twofold or three-fold symmetry. A study of different meta-stable configurations with same number of vortices is also presented. Next, by taking into account de Gennes boundary conditions via the extrapolation length, b, we study the properties of a mesoscopic superconducting square surrounded by different metallic materials and in the presence of an external magnetic field applied perpendicularly to the square surface. It is determined the b  -limit for the occurrence of a single vortex in a mesoscopic square of area d²$d^2$, for 4ξ(0)?d?10ξ(0)$4\xi (0)?d?10\xi (0)$.     

Resonance detection of dark matter axions using a DC SQUID

A method for detecting dark matter axions in which a dc SQUID serves as a detector is proposed. The SQUID is shown to be able to detect the magnetic field perturbations induced by its interaction with axions. The resonance signal appears as a current step in the SQUID current–voltage characteristic. The voltage of the step corresponds to the axion mass, while its height depends on the axion energy density in near-Earth space. The proposed method is aimed at detecting axions with masses m_a ? 10^–4 eV, which are of interest for both cosmology and particle physics.     

Three-dimensional constitutive equations for Ni–Mn–Ga single crystals

This paper presents a formulation of isothermal three-dimensional (3D) quasi-static magneto-mechanical constitutive equations and 3D magnetisation constitutive equations for tetragonal martensite Ni–Mn–Ga FSMA single crystals (c/a<1)$(c/a<1)$ with both ends restrained from twin-boundary motion. The formulated 3D constitutive equations model the 3D quasi-static magnetic fields as well as the coupling between uniaxial strains and stresses, and shear strains and stresses. The constitutive equations are compared with experimental results available in the literature and are found to correlate well with the experimental results, including magnetic field reversals. Both sets of 3D constitutive equations require only macroscopic parameters that are readily obtainable from magnetisation and mechanical stress–strain curves.     

The spectrum of open string field theory at the stable tachyonic vacuum

We present a level (10,30)$(10,30)$ numerical computation of the spectrum of quadratic fluctuations of open string field theory around the tachyonic vacuum, both in the scalar and in the vector sector. Our results are consistent with Sen's conjecture about gauge-triviality of the small excitations. The computation is sufficiently accurate to provide robust evidence for the absence of the photon from the open string spectrum. We also observe that ghost string field propagators develop double poles. We show that this requires non-empty BRST cohomologies at non-standard ghost numbers. We comment about the relations of our results with recent work on the same subject.     

Anisotropic harmonic oscillator,non-commutative Landau problem and exotic Newton–Hooke symmetry

We investigate the planar anisotropic harmonic oscillator with explicit rotational symmetry as a particle model with non-commutative coordinates. It includes the exotic Newton–Hooke particle and the non-commutative Landau problem as special, isotropic and maximally anisotropic, cases. The system is described by the same (2+1$2+1$)-dimensional exotic Newton–Hooke symmetry as in the isotropic case, and develops three different phases depending on the values of the two central charges. The special cases of the exotic Newton–Hooke particle and non-commutative Landau problem are shown to be characterized by additional, so(3)$\mathit{so}(3)$ or so(2,1)$\mathit{so}(2,1)$ Lie symmetry, which reflects their peculiar spectral properties.     

Analytical approximation schemes for solving exact renormalization group equations. II Conformal mappings

We present a new efficient analytical approximation scheme to two-point boundary value problems of ordinary differential equations (ODEs) adapted to the study of the derivative expansion of the exact renormalization group equations. It is based on a compactification of the complex plane of the independent variable using a mapping of an angular sector onto a unit disc. We explicitly treat, for the scalar field, the local potential approximations of the Wegner–Houghton equation in the dimension d=3$d=3$ and of the Wilson–Polchinski equation for some values of d∈]2,3]$d\in ]2,3]$. We then consider, for d=3$d=3$, the coupled ODEs obtained by Morris at the second order of the derivative expansion. In both cases the fixed points and the eigenvalues attached to them are estimated. Comparisons of the results obtained are made with the shooting method and with the other analytical methods available. The best accuracy is reached with our new method which presents also the advantage of being very fast. Thus, it is well adapted to the study of more complicated systems of equations.     

Self-force on a scalar point charge in the long throat

An analytic method is presented which allows for the computation of the self-force for a static particle with a scalar charge in the region of an ultrastatic spacetime which one can call the long throat. The method is based on the approximate WKB solution of a radial mode equation for a scalar field. This field is assumed to be massless, with a coupling ξ   to the scalar curvature is satisfying the condition ξ>1/8$\xi >1/8$.