QED radiative corrections to the decay pi^0 to e^+e^-

We reconsider QED radiative corrections (RC) to the $\pi^{0}\to e^{+}e^{-}$ decay width. One kind of RC investigated earlier has a renormalization group origin and can be associated with the final state interaction of electron and positron. It determines the distribution of lepton pair invariant masses in the whole kinematic region. The other type of RC has a double-logarithmic character and is related to almost on-mass-shell behavior of the lepton form factors. The total effect of RC for the $\pi^{0}\to e^{+}e^{-}$ decay is estimated to be 3.2% and for the decay $\eta \to e^{+}e^{-}$ is 4.3%.Comment: 12 pages, 3 figure

Can multi-TeV (top and other) squarks be natural in gauge mediation?

We investigate whether multi-TeV (1-3 TeV) squarks can be natural in models of gauge mediated SUSY breaking. The idea is that for some boundary condition of the scalar (Higgs and stop) masses, the Higgs (mass)$^2$, evaluated at the renormalization scale $\sim O(100)$ GeV, is not very sensitive to (boundary values of) the scalar masses (this has been called ``focussing'' in recent literature). Then, the stop masses can be multi-TeV without leading to fine-tuning in electroweak symmetry breaking. {\em Minimal} gauge mediation does {\em not} lead to this focussing (for all values of $\tan \beta$ and the messenger scale): the (boundary value of) the Higgs mass is too small compared to the stop masses. Also, in minimal gauge mediation, the gaugino masses are of the same order as the scalar masses so that multi-TeV scalars implies multi-TeV gauginos (especially gluino) leading to fine-tuning. We discuss ideas to {\em increase} the Higgs mass relative to the stop masses (so that focussing can be achieved) and also to {\em suppress} gaugino masses relative to scalar masses (or to modify the gaugino mass relations) in {\em non-minimal} models of gauge mediation -- then multi-TeV (top and other) squarks can be natural. Specific models of gauge mediation which incorporate these ideas and thus have squarks (and in some cases, the gluino) heavier than a TeV without resulting in fine-tuning are also studied and their collider signals are contrasted with those of other models which have multi-TeV squarks.Comment: LaTeX, 29 pages, 9 eps figures. Replacing an earlier version. In version 3, some references and a minor comment have been added and typos have been correcte

Effect of mass transport on the electrochemical oxidation of alcohols over electrodeposited film and carbon-supported pt electrodes

© 2018 The Author(s) Electrochemical oxidation of four different alcohol molecules (methanol, ethanol, n-butanol and 2-butanol) at electrodeposited Pt film and carbon-supported Pt catalyst film electrodes, as well as the effect of mass transport on the oxidation reaction, has been studied systematically using the rotating disk electrode (RDE) technique. It was shown that oxidation current decreased with an increase in the rotation rate (ω) for all alcohols studied over electrodeposited Pt film electrodes. In contrast, the oxidation current was found to increase with an increase in the ω for Pt/C in ethanol and n-butanol-containing solutions. The decrease was found to be nearly reversible for ethanol and n-butanol at the electrodeposited Pt film electrode ruling out the possibility of intermediate CO ads poisoning being the sole cause of the decrease and was attributed to the formation of soluble intermediate species which diffuse away from the electrode at higher ω. In contrast, an increase in the current with an increase in ω for the carbon supported catalyst may suggest that the increase in residence time of the soluble species within the catalyst layer, results in further oxidation of these species. Furthermore, the reversibility of the peak current on decreasing the ω could indicate that the surface state has not significantly changed due to the sluggish reaction kinetics of ethanol and n-butanol

Quiver theories, soliton spectra and Picard-Lefschetz transformations

Quiver theories arising on D3-branes at orbifold and del Pezzo singularities are studied using mirror symmetry. We show that the quivers for the orbifold theories are given by the soliton spectrum of massive 2d N=2 theory with weighted projective spaces as target. For the theories obtained from the del Pezzo singularities we show that the geometry of the mirror manifold gives quiver theories related to each other by Picard-Lefschetz transformations, a subset of which are simple Seiberg duals. We also address how one indeed derives Seiberg duality on the matter content from such geometrical transitions and how one could go beyond and obtain certain ``fractional Seiberg duals.'' Moreover, from the mirror geometry for the del Pezzos arise certain Diophantine equations which classify all quivers related by Picard-Lefschetz. Some of these Diophantine equations can also be obtained from the classification results of Cecotti-Vafa for the 2d N=2 theories.Comment: 34 pages, 11 figure

Color Superconducting Phases of Cold Dense Quark Matter

We investigate color superconducting phases of cold quark matter at densities relevant for the interiors of compact stars. At these densities, electrically neutral and weak-equilibrated quark matter can have unequal numbers of up, down, and strange quarks. The QCD interaction favors Cooper pairs that are antisymmetric in color and in flavor, and a crystalline color superconducting phase can occur which accommodates pairing between flavors with unequal number densities. In the crystalline color superconductor, quarks of different flavor form Cooper pairs with nonzero total momentum, yielding a condensate that varies in space like a sum of plane waves. Rotational and translational symmetry are spontaneously broken. We use a Ginzburg-Landau method to evaluate candidate crystal structures and predict that the favored structure is face-centered-cubic. We predict a robust crystalline phase with gaps comparable in magnitude to those of the color-flavor-locked phase that occurs when the flavor number densities are equal. Crystalline color superconductivity will be a generic feature of the QCD phase diagram, occurring wherever quark matter that is not color-flavor locked is to be found. If a very large flavor asymmetry forbids even the crystalline state, single-flavor pairing will occur; we investigate this and other spin-one color superconductors in a survey of generic color, flavor, and spin pairing channels. Our predictions for the crystalline phase may be tested in an ultracold gas of fermionic atoms, where a similar crystalline superfluid state can occur. If a layer of crystalline quark matter occurs inside of a compact star, it could pin rotational vortices, leading to observable pulsar glitches.Comment: Ph.D. thesis, submitted to the MIT Department of Physics, May 2003. Five chapters and two appendices (180 pages, 30 figures). Chapters 1 and 5 are new: chapter 1 is a detailed review of previous work, and chapter 5 discusses applications of the crystalline phase for the physics of pulsar spin glitches and cold trapped atom

Dibaryons from Exceptional Collections

We discuss aspects of the dictionary between brane configurations in del Pezzo geometries and dibaryons in the dual superconformal quiver gauge theories. The basis of fractional branes defining the quiver theory at the singularity has a K-theoretic dual exceptional collection of bundles which can be used to read off the spectrum of dibaryons in the weakly curved dual geometry. Our prescription identifies the R-charge R and all baryonic U(1) charges Q_I with divisors in the del Pezzo surface without any Weyl group ambiguity. As one application of the correspondence, we identify the cubic anomaly tr R Q_I Q_J as an intersection product for dibaryon charges in large-N superconformal gauge theories. Examples can be given for all del Pezzo surfaces using three- and four-block exceptional collections. Markov-type equations enforce consistency among anomaly equations for three-block collections.Comment: 47 pages, 11 figures, corrected ref

Dibaryon Spectroscopy

The AdS/CFT correspondence relates dibaryons in superconformal gauge theories to holomorphic curves in Kaehler-Einstein surfaces. The degree of the holomorphic curves is proportional to the gauge theory conformal dimension of the dibaryons. Moreover, the number of holomorphic curves should match, in an appropriately defined sense, the number of dibaryons. Using AdS/CFT backgrounds built from the generalized conifolds of Gubser, Shatashvili, and Nekrasov (1999), we show that the gauge theory prediction for the dimension of dibaryonic operators does indeed match the degree of the corresponding holomorphic curves. For AdS/CFT backgrounds built from cones over del Pezzo surfaces, we are able to match the degree of the curves to the conformal dimension of dibaryons for the n'th del Pezzo surface, n=1,2,...,6. Also, for the del Pezzos and the A_k type generalized conifolds, for the dibaryons of smallest conformal dimension, we are able to match the number of holomorphic curves with the number of possible dibaryon operators from gauge theory.Comment: 30 pages, 6 figures, corrected refs; v3 typos correcte

Curvature Inspired Cosmological Scenario

Using modified gravity with non-linear terms of curvature, $R^2$ and $R^{(r +2)}$ (with $r$ being the positive real number and $R$ being the scalar curvature), cosmological scenario,beginning at the Planck scale, is obtained. Here, a unified picture of cosmology is obtained from $f(R)-$ gravity. In this scenario, universe begins with power-law inflation, followed by deceleration and acceleration in the late universe as well as possible collapse of the universe in future. It is different from $f(R)-$ dark energy models with non-linear curvature terms assumed as dark energy. Here, dark energy terms are induced by linear as well as non-linear terms of curvature in Friedmann equation being derived from modified gravity.It is also interesting to see that, in this model, dark radiation and dark matter terms emerge spontaneously from the gravitational sector. It is found that dark energy, obtained here, behaves as quintessence in the early universe and phantom in the late universe. Moreover, analogous to brane-tension in brane-gravity inspired Friedmann equation, a tension term $\lambda$ arises here being called as cosmic tension. It is found that, in the late universe, Friedmann equation (obtained here) contains a term $- \rho^2/2\lambda$ ($\rho$ being the phantom energy density) analogous to a similar term in Friedmann equation with loop quantum effects, if $\lambda > 0$ and brane-gravity correction when $\lambda < 0.$Comment: 19 Pages. To appear in Int. J. Thro. Phy

Decaying Hidden Dark Matter in Warped Compactification

The recent PAMELA and ATIC/Fermi/HESS experiments have observed an excess of electrons and positrons, but not anti-protons, in the high energy cosmic rays. To explain this result, we construct a decaying hidden dark matter model in string theory compactification that incorporates the following two ingredients, the hidden dark matter scenario in warped compactification and the phenomenological proposal of hidden light particles that decay to the Standard Model. In this model, on higher dimensional warped branes, various warped Kaluza-Klein particles and the zero-mode of gauge field play roles of the hidden dark matter or mediators to the Standard Model.Comment: 15 pages; v4, several clarifications added, update on Fermi/HESS result

Detecting Physics At The Post-GUT And String Scales By Linear Colliders

The ability of linear colliders to test physics at the post-GUT scale is investigated. Using current estimates of measurements available at such accelerators, it is seen that soft breaking masses can be measured with errors of about (1-20)%. Three classes of models in the post-GUT region are examined: models with universal soft breaking masses at the string scale, models with horizontal symmetry, and string models with Calabi-Yau compactifications. In each case, linear colliders would be able to test directly theoretical assumptions made at energies beyond the GUT scale to a good accuracy, distinguish between different models, and measure parameters that are expected to be predictions of string models.Comment: Latex, 21 pages, no figure