Wavy Strings: Black or Bright?

Recent developments in string theory have brought forth a considerable interest in time-dependent hair on extended objects. This novel new hair is typically characterized by a wave profile along the horizon and angular momentum quantum numbers $l,m$ in the transverse space. In this work, we present an extensive treatment of such oscillating black objects, focusing on their geometric properties. We first give a theorem of purely geometric nature, stating that such wavy hair cannot be detected by any scalar invariant built out of the curvature and/or matter fields. However, we show that the tidal forces detected by an infalling observer diverge at the `horizon' of a black string superposed with a vibration in any mode with $l \ge 1$. The same argument applied to longitudinal ($l=0$) waves detects only finite tidal forces. We also provide an example with a manifestly smooth metric, proving that at least a certain class of these longitudinal waves have regular horizons.Comment: 45 pages, latex, no figure

Superheavy Dark Matter with Discrete Gauge Symmetries

We show that there are discrete gauge symmetries protect naturally heavy X particles from decaying into the ordinary light particles in the supersymmetric standard model. This makes the proposal very attractive that the superheavy X particles constitute a part of the dark matter in the present universe. It is more interesting that there are a class of discrete gauge symmetries which naturally accommodate a long-lived unstable X particle. We find that in some discrete Z_{10} models, for example, a superheavy X particle has lifetime \tau_X \simeq 10^{11}-10^{26} years for its mass M_X \simeq 10^{13}-10^{14} GeV. This long lifetime is guaranteed by the absence of lower dimensional operators (of light particles) couple to the X. We briefly discuss a possible explanation for the recently observed ultra-high-energy cosmic ray events by the decay of this unstable X particle.Comment: 9 pages, Late

Quantum Theory of Noncommutative Fields

Generalizing the noncommutative harmonic oscillator construction, we propose a new extension of quantum field theory based on the concept of "noncommutative fields". Our description permits to break the usual particle-antiparticle degeneracy at the dispersion relation level and introduces naturally an ultraviolet and an infrared cutoff. Phenomenological bounds for these new energy scales are given.Comment: LaTeX file, JHEP3.cls, subequations.sty; 12 pages, no figures. Final version published in JHEP with some references adde

On the Spin Gap Phase of Strongly-Correlated Electrons

We discuss the possible existence of a spin-gap phase in the low-doping regime of strongly-correlated two-dimensional electrons within the gauge field description of the t-J model. The spin-gap phase was recently shown by Ubbens and Lee to be destroyed by gauge field quantum fluctuations for a single-layer 2D system in the absence of disorder and for a full gap. We show that the same conclusion applies both in the dirty limit and for the case of a gapless spinon condensate.Comment: 7 pages, uuencoded Postscript, including 1 figur

Holographic Description of AdS Cosmologies

To gain insight in the quantum nature of the big bang, we study the dual field theory description of asymptotically anti-de Sitter solutions of supergravity that have cosmological singularities. The dual theories do not appear to have a stable ground state. One regularization of the theory causes the cosmological singularities in the bulk to turn into giant black holes with scalar hair. We interpret these hairy black holes in the dual field theory and use them to compute a finite temperature effective potential. In our study of the field theory evolution, we find no evidence for a "bounce" from a big crunch to a big bang. Instead, it appears that the big bang is a rare fluctuation from a generic equilibrium quantum gravity state.Comment: 34 pages, 8 figures, v2: minor changes, references adde

Conservation Laws in Doubly Special Relativity

Motivated by various theoretical arguments that the Planck energy (Ep - 10^19 GeV) - should herald departures from Lorentz invariance, and the possibility of testing these expectations in the not too distant future, two so-called "Doubly Special Relativity" theories have been suggested -- the first by Amelino-Camelia (DSR1) and the second by Smolin and Magueijo (DSR2). These theories contain two fundamental scales -- the speed of light and an energy usually taken to be Ep. The symmetry group is still the Lorentz group, but in both cases acting nonlinearly on the energy-momentum sector. Accordingly, since energy and momentum are no longer additive quantities, finding their values for composite systems (and hence finding the correct conservation laws) is a nontrivial matter. Ultimately it is these possible deviations from simple linearly realized relativistic kinematics that provide the most promising observational signal for empirically testing these models. Various investigations have narrowed the conservation laws down to two possibilities per DSR theory. We derive unique exact results for the energy-momentum of composite systems in both DSR1 and DSR2, and indicate the general strategy for arbitrary nonlinear realizations of the Lorentz group.Comment: V2: Extensive revisions: merged with gr-qc/0205093, new author added, references added, discussion amplified. 4 pages, revtex4; V3: Revised in response to referee comments; no physics changes; version to appear in Physical Review

Lorentz invariance violation in top-down scenarios of ultrahigh energy cosmic ray creation

The violation of Lorentz invariance (LI) has been invoked in a number of ways to explain issues dealing with ultrahigh energy cosmic ray (UHECR) production and propagation. These treatments, however, have mostly been limited to examples in the proton-neutron system and photon-electron system. In this paper we show how a broader violation of Lorentz invariance would allow for a series of previously forbidden decays to occur, and how that could lead to UHECR primaries being heavy baryonic states or Higgs bosons.Comment: Replaced with heavily revised (see new Abstract) version accepted by Phys. Rev. D. 6 page

Management of Lasiodiplodia theobromae , the causal agent of mango tree decline disease in Ghana

Mango ( Mangifera indica L.), is one of the economically most important crops in Ghana. It is recognised for its popularity in contributing to food and nutritional security. Despite its economic importance, mango tree decline disease, caused by Lasiodiplodia theobromae, poses a serious threat to the mango industry in the country. The objective of this study was to evaluate fungicides (i.e., carbendazim, zamir, mancozeb, funguran and sulphur 80) and bio pesticides ( Chromolaena odorata , Azadirachta indica and Carica papaya ) against L. theobromae. The results showed that all the tested fungicides, except for sulphur 80, inhibited mycelial radial growth of L. theobromae, with carbendazim and funguran improving the vegetative growth of the shoots and leaves in the field. Mango trees treated with carbendazim, after the third spray, had no disease symptoms. However, application of urea fertiliser and carbendazim (50 g 15 L-1 water), at a two-week spraying interval in the field, reduced the severity of L. theobromae. Application of biopesticides (plant extracts) showed that C. odorata had the highest efficacy, followed by A. indica and then C. papaya. Although further studies on plant extracts in the field are required, our findings provide important information for the development of integrated management strategies for the pathogen, and the disease it transmits.La mangue ( Mangifera indica L.) est l\u2019une des cultures les plus importantes \ue9conomiquement au Ghana. Il est reconnu pour sa popularit\ue9 en contribuant \ue0 la s\ue9curit\ue9 alimentaire et nutritionnelle. Malgr\ue9 son importance \ue9conomique, la maladie du d\ue9clin du manguier, caus\ue9e par Lasiodiplodia theobromae , constitue une menace s\ue9rieuse pour l\u2019industrie de la mangue dans le pays. L\u2019objectif de cette \ue9tude \ue9tait d\u2019\ue9valuer les fongicides (c\u2019est-\ue0-dire le carbendazime, le zamir, le mancoz\ue8be, le fonguran et le soufre 80) et les pesticides biologiques ( Chromolaena odorata , Azadirachta indica et Carica papaya ) contre L. theobromae. Les r\ue9sultats ont montr\ue9 que tous les fongicides test\ue9s, \ue0 l\u2019exception du soufre 80, inhibaient la croissance radiale myc\ue9lienne de L. theobromae, le carbendazime et le fonguran am\ue9liorant la croissance v\ue9g\ue9tative des pousses et des feuilles au champ. Les manguiers trait\ue9s au carbendazime apr\ue8s la troisi\ue8me pulv\ue9risation ne pr\ue9sentaient aucun sympt\uf4me de maladie. Cependant, l\u2019application d\u2019engrais \ue0 base d\u2019ur\ue9e et de carbendazime (50 g 15 L-1 d\u2019eau) \ue0 un intervalle de pulv\ue9risation de deux semaines dans le champ a r\ue9duit la gravit\ue9 de L. theobromae. L\u2019application de biopesticides (extraits de plantes) a montr\ue9 que C. odorata avait la plus grande efficacit\ue9, suivie par A. indica et ensuite C. papaya. Bien que des \ue9tudes suppl\ue9mentaires sur les extraits de plantes sur le terrain soient n\ue9cessaires, nos r\ue9sultats fournissent des informations importantes pour le d\ue9veloppement de strat\ue9gies de gestion int\ue9gr\ue9e du pathog\ue8ne et de la maladie qu\u2019il transmet

Renormalization-Group Improved Effective Potential for Interacting Theories with Several Mass Scales in Curved Spacetime

The renormalization group (RG) is used in order to obtain the RG improved effective potential in curved spacetime. This potential is explicitly calculated for the Yukawa model and for scalar electrodynamics, i.e. theories with several (namely, more than one) mass scales, in a space of constant curvature. Using the $\lambda \varphi^4$-theory on a general curved spacetime as an example, we show how it is possible to find the RG improved effective Lagrangian in curved spacetime. As specific applications, we discuss the possibility of curvature induced phase transitions in the Yukawa model and the effective equations (back-reaction problem) for the $\lambda \varphi^4$-theory on a De Sitter background.Comment: 18 pages, LaTeX file, UB-ECM-PF 93/2

Moduli and (un)attractor black hole thermodynamics

We investigate four-dimensional spherically symmetric black hole solutions in gravity theories with massless, neutral scalars non-minimally coupled to gauge fields. In the non-extremal case, we explicitly show that, under the variation of the moduli, the scalar charges appear in the first law of black hole thermodynamics. In the extremal limit, the near horizon geometry is $AdS_2\times S^2$ and the entropy does not depend on the values of moduli at infinity. We discuss the attractor behaviour by using Sen's entropy function formalism as well as the effective potential approach and their relation with the results previously obtained through special geometry method. We also argue that the attractor mechanism is at the basis of the matching between the microscopic and macroscopic entropies for the extremal non-BPS Kaluza-Klein black hole.Comment: 36 pages, no figures, V2: minor changes, misprints corrected, expanded references; V3: sections 4.3 and 4.5 added; V4: minor changes, matches the published versio