You Can't Get Through Szekeres Wormholes - or - Regularity, Topology and Causality in Quasi-Spherical Szekeres Models

The spherically symmetric dust model of Lemaitre-Tolman can describe wormholes, but the causal communication between the two asymptotic regions through the neck is even less than in the vacuum (Schwarzschild-Kruskal-Szekeres) case. We investigate the anisotropic generalisation of the wormhole topology in the Szekeres model. The function E(r, p, q) describes the deviation from spherical symmetry if \partial_r E \neq 0, but this requires the mass to be increasing with radius, \partial_r M > 0, i.e. non-zero density. We investigate the geometrical relations between the mass dipole and the locii of apparent horizon and of shell-crossings. We present the various conditions that ensure physically reasonable quasi-spherical models, including a regular origin, regular maxima and minima in the spatial sections, and the absence of shell-crossings. We show that physically reasonable values of \partial_r E \neq 0 cannot compensate for the effects of \partial_r M > 0 in any direction, so that communication through the neck is still worse than the vacuum. We also show that a handle topology cannot be created by identifying hypersufaces in the two asymptotic regions on either side of a wormhole, unless a surface layer is allowed at the junction. This impossibility includes the Schwarzschild-Kruskal-Szekeres case.Comment: zip file with LaTeX text + 6 figures (.eps & .ps). 47 pages. Second replacement corrects some minor errors and typos. (First replacement prints better on US letter size paper.

Electromagnetic wave propagation inside a material medium: an effective geometry interpretation

We present a method developed to deal with electromagnetic wave propagation inside a material medium that reacts, in general, non-linearly to the field strength. We work in the context of Maxwell' s theory in the low frequency limit and obtain a geometrical representation of light paths for each case presented. The isotropic case and artificial birefringence caused by an external electric field are analyzed as an application of the formalism and the effective geometry associated to the wave propagation is exhibited.Comment: REVTeX file, 6 pages. Version to appear in Phys. Lett.

Consistency analysis of a nonbirefringent Lorentz-violating planar model

In this work analyze the physical consistency of a nonbirefringent Lorentz-violating planar model via the analysis of the pole structure of its Feynman propagators. The nonbirefringent planar model, obtained from the dimensional reduction of the CPT-even gauge sector of the standard model extension, is composed of a gauge and a scalar fields, being affected by Lorentz-violating (LIV) coefficients encoded in the symmetric tensor $\kappa_{\mu\nu}$. The propagator of the gauge field is explicitly evaluated and expressed in terms of linear independent symmetric tensors, presenting only one physical mode. The same holds for the scalar propagator. A consistency analysis is performed based on the poles of the propagators. The isotropic parity-even sector is stable, causal and unitary mode for $0\leq\kappa_{00}<1$. On the other hand, the anisotropic sector is stable and unitary but in general noncausal. Finally, it is shown that this planar model interacting with a $\lambda|\varphi|^{4}-$Higgs field supports compactlike vortex configurations.Comment: 11 pages, revtex style, final revised versio

Effective Action for QED with Fermion Self-Interaction in D=2 and D=3 Dimensions

In this work we discuss the effect of the quartic fermion self-interaction of Thirring type in QED in D=2 and D=3 dimensions. This is done through the computation of the effective action up to quadratic terms in the photon field. We analyze the corresponding nonlocal photon propagators nonperturbatively in % \frac{k}{m}, where k is the photon momentum and m the fermion mass. The poles of the propagators were determined numerically by using the Mathematica software. In D=2 there is always a massless pole whereas for strong enough Thirring coupling a massive pole may appear . For D=3 there are three regions in parameters space. We may have one or two massive poles or even no pole at all. The inter-quark static potential is computed analytically in D=2. We notice that the Thirring interaction contributes with a screening term to the confining linear potential of massive QED_{2}. In D=3 the static potential must be calculated numerically. The screening nature of the massive QED$_{3}$ prevails at any distance, indicating that this is a universal feature of % D=3 electromagnetic interaction. Our results become exact for an infinite number of fermion flavors.Comment: Latex, 13 pages, 3 figure

Influence Of Spin Reorientation On Magnetocaloric Effect In Nd Al2: A Microscopic Model

We report a theoretical investigation about the influence of the spin reorientation from easy magnetic direction 001 to the applied magnetic field direction 111 on the magnetocaloric properties of Nd Al2. This compound was fully investigated using a model Hamiltonian which includes the Zeeman-exchange interactions and the crystalline electrical field, which are responsible for the magnetic anisotropy. All theoretical results were obtained using the proper model parameters for Nd Al2, found in the literature. The existence of a minimum in magnetic entropy change below the phase transition was predicted and ascribed to the strong jump on the spin reorientation. © 2006 The American Physical Society.745Tishin, A.M., Spichkin, Y.I., (2003) The Magnetocaloric Effect and Its Applications, , Institute of Physics, BristolPecharsky, V.K., Gschneidner Jr., K.A., (1997) Phys. Rev. Lett., 78, p. 4494. , PRLTAO 0031-9007 10.1103/PhysRevLett.78.4494Tegus, O., Brück, E., Buschow, K.H.J., De Boer, F.R., (2002) Nature, 415, p. 150. , NATUAS 0028-0836 10.1038/415150AWada, H., Tanabe, Y., (2001) Appl. Phys. Lett., 79, p. 3302. , APPLAB 0003-6951Wada, H., Morikawa, T., Taniguchi, K., Shibata, T., Yamada, Y., Akishige, Y., (2003) Physica B, 328, p. 114. , PHYBE3 0921-4526 10.1016/S0921-4526(02)01822-7Hu, F., Shen, B., Sun, J., Cheng, Z., Rao, G., Zhang, X., (2001) Appl. Phys. Lett., 78, p. 3675. , APPLAB 0003-6951Fujita, A., Fujieda, S., Hasegawa, Y., Fukamichi, K., (2003) Phys. Rev. B, 67, p. 104416. , PRBMDO 0163-1829 10.1103/PhysRevB.67.104416Brown, G.V., (1976) J. Appl. Phys., 47, p. 3673. , JAPIAU 0021-8979 10.1063/1.323176Von Ranke, P.J., De Oliveira, N.A., Gama, S., (2004) J. Magn. Magn. Mater., 277, p. 78. , JMMMDC 0304-8853 10.1016/j.jmmm.2003.10.013Von Ranke, P.J., De Oliveira, N.A., Gama, S., (2004) Phys. Lett. a, 320, p. 302. , PYLAAG 0375-9601 10.1016/j.physleta.2003.10.067Von Ranke, P.J., De Campos, A., Caron, L., Coelho, A.A., Gama, S., De Oliveira, N.A., (2004) Phys. Rev. B, 70, p. 094410. , PRBMDO 0163-1829 10.1103/PhysRevB.70.094410Gama, S., Coelho, A.A., De Campos, A., Carvalho, A.M., Gandra, F.C.G., Von Ranke, P., De Oliveira, N.A., (2004) Phys. Rev. Lett., 93, p. 237202. , PRLTAO 0031-9007 10.1103/PhysRevLett.93.237202Von Ranke, P.J., De Oliveira, N.A., Mello, C., Carvalho, A.M., Gama, S., (2005) Phys. Rev. B, 71, p. 054410. , PRBMDO 0163-1829 10.1103/PhysRevB.71.054410Von Ranke, P.J., Gama, S., Coelho, A.A., De Campos, A., Carvalho, A.M., Gandra, F.C.G., De Oliveira, N.A., (2006) Phys. Rev. B, 73, p. 014415. , PRBMDO 0163-1829 10.1103/PhysRevB.73.014415Von Ranke, P.J., Pecharsky, V.K., Gschneidner, K.A., Korte, B.J., (1998) Phys. Rev. B, 58, p. 14436. , PRBMDO 0163-1829 10.1103/PhysRevB.58.14436Von Ranke, P.J., Mota, M.A., Grangeia, D.F., Carvalho, A.M., Gandra, F.C.G., Coelho, A.A., Caldas, A., Gama, S., (2004) Phys. Rev. B, 70, p. 134428. , PRBMDO 0163-1829 10.1103/PhysRevB.70.134428Lima, A.L., Tsokol, A.O., Gschneidner Jr., K.A., Pecharsky, V.K., Lograsso, T.A., Schlagel, D.L., (2005) Phys. Rev. B, 72, p. 024403. , PRBMDO 0163-1829 10.1103/PhysRevB.72.024403Von Ranke, P.J., De Oliveira, I.G., Guimaraes, A.P., Da Silva, X.A., (2000) Phys. Rev. B, 61, p. 447. , PRBMDO 0163-1829 10.1103/PhysRevB.61.447Lea, K.R., Leask, M.J.M., Wolf, W.P., (1962) J. Phys. Chem. Solids, 33, p. 1381. , JPCSAW 0022-3697Stevens, K.W.H., (1952) Proc. Phys. Soc., London, Sect. a, 65, p. 209. , PPSAAM 0370-1298 10.1088/0370-1298/65/3/308Purwins, H.G., Leson, A., (1990) Adv. Phys., 39, p. 309. , ADPHAH 0001-8732 10.1080/00018739000101511Bak, P., (1974) J. Phys. C, 7, p. 4097. , JPSOAW 0022-3719 10.1088/0022-3719/7/22/014Nereson, N., Olsen, C., Arnold, G., (1996) J. Appl. Phys., 37, p. 4575. , JAPIAU 0021-8979 10.1063/1.1708083Deenadas, C., Thompson, A.W., Graig, R.S., Wallace, W.E., (1971) J. Phys. Chem. Solids, 32, p. 1843. , JPCSAW 0022-3697Inoue, T., Sankar, S.G., Graig, R.S., Wallace, W.E., Gschneidner Jr., K.A., (1997) J. Phys. Chem. Solids, 38, p. 487. , JPCSAW 0022-3697Barbara, B., Boucherle, J.X., Michelutti, B., Rossignol, M.F., (1979) Solid State Commun., 31, p. 477. , SSCOA4 0038-1098Barbara, B., Rossignol, M.F., Boucherle, J.X., (1975) Phys. Lett., 55, p. 321. , PYLAAG 0375-9601 10.1016/0375-9601(75)90489-

Magnetocaloric Effect Due To Spin Reorientation In The Crystalline Electrical Field: Theory Applied To Dy Al2

We report a way of obtaining the magnetocaloric effect due to the crystal electrical-field quenching of the total angular momentum in a magnetic system where a strong spin reorientation is present. The theoretical model is applied to Dy Al2 and the results predict a considerable magnetic entropy change by rotating a single crystal in a fixed magnetic field. The obtained temperature and magnetic-field dependencies of the magnetization component along the 111-crystallographic direction are in good agreement with the recently reported experimental data. © 2007 The American Physical Society.7518Pecharsky, V.K., Gschneidner Jr., K.A., (1997) Phys. Rev. Lett., 78, p. 4494. , PRLTAO 0031-9007 10.1103/PhysRevLett.78.4494Choe, W., Pecharsky, V.K., Pecharsky, A.O., Gschneidner Jr., K.A., Young Jr., V.G., Miller, G.J., (2000) Phys. Rev. Lett., 84, p. 4617. , PRLTAO 0031-9007 10.1103/PhysRevLett.84.4617Provenzano, V., Shapiro, A.J., Shull, R.D., (2004) Nature (London), 429, p. 853. , NATUAS 0028-0836 10.1038/nature02657Tegus, O., Brück, E., Buschow, K.H.J., De Boer, F.R., (2002) Nature (London), 415, p. 150. , NATUAS 0028-0836 10.1038/415150AWada, H., Tanabe, Y., (2001) Appl. Phys. Lett., 79, p. 3302. , APPLAB 0003-6951 10.1063/1.1419048Wada, H., Morikawa, T., Taniguchi, K., Shibata, T., Yamada, Y., Akishige, Y., (2003) Physica B, 328, p. 114. , PHYBE3 0921-4526 10.1016/S0921-4526(02)01822-7Hu, F., Shen, B., Sun, J., Cheng, Z., Rao, G., Zhang, X., (2001) Appl. Phys. Lett., 78, p. 3675. , APPLAB 0003-6951 10.1063/1.1375836Fujita, A., Fujieda, S., Hasegawa, Y., Fukamichi, K., (2003) Phys. Rev. B, 67, p. 104416. , PRBMDO 0163-1829 10.1103/PhysRevB.67.104416Von Ranke, P.J., De Oliveira, N.A., Gama, S., (2004) J. Magn. Magn. Mater., 277, p. 78. , JMMMDC 0304-8853 10.1016/j.jmmm.2003.10.013Von Ranke, P.J., De Campos, N.A., Caron, L., Coelho, A.A., Gama, S., De Oliveira, N.A., (2004) Phys. Rev. B, 70, p. 094410. , PRBMDO 0163-1829 10.1103/PhysRevB.70.094410Von Ranke, P.J., De Oliveira, N.A., Gama, S., (2004) Phys. Lett. a, 320, p. 302. , PYLAAG 0375-9601 10.1016/j.physleta.2003.10.067Gama, S., Coelho, A.A., De Campos, A., Carvalho, A.M., Gandra, F.C.G., Von Ranke, P.J., De Oliveira, N.A., (2004) Phys. Rev. Lett., 93, p. 237202. , PRLTAO 0031-9007 10.1103/PhysRevLett.93.237202Von Ranke, P.J., De Oliveira, N.A., Mello, C., Carvalho, A.M., Gama, S., (2005) Phys. Rev. B, 71, p. 054410. , PRBMDO 0163-1829 10.1103/PhysRevB.71.054410Von Ranke, P.J., Gama, S., Coelho, A.A., De Campos, A., Carvalho, A.M., Gandra, F.C.G., De Oliveira, N.A., (2006) Phys. Rev. B, 73, p. 014415. , PRBMDO 0163-1829 10.1103/PhysRevB.73.014415Von Ranke, P.J., Pecharsky, V.K., Gschneidner, K.A., Korte, B.J., (1998) Phys. Rev. B, 58, p. 14436. , PRBMDO 0163-1829 10.1103/PhysRevB.58.14436Von Ranke, P.J., Mota, M.A., Grangeia, D.F., Carvalho, A.M., Gandra, F.C.G., Coelho, A.A., Caldas, A., Gama, S., (2004) Phys. Rev. B, 70, p. 134428. , PRBMDO 0163-1829 10.1103/PhysRevB.70.134428Lima, A.L., Oliveira, I.S., Gomes, A.M., Von Ranke, P.J., (2002) Phys. Rev. B, 65, p. 172411. , PRBMDO 0163-1829 10.1103/PhysRevB.65.172411Von Ranke, P.J., Lima, A.L., Nobrega, E.P., Da Silva, X.A., Guimarães, A.P., Oliveira, I.S., (2000) Phys. Rev. B, 63, p. 024422. , PRBMDO 0163-1829 10.1103/PhysRevB.63.024422Lima, A.L., Tsokol, A.O., Gschneidner Jr., K.A., Pecharky, V.K., Lograsso, T.A., Schlagel, D.L., (2005) Phys. Rev. B, 72, p. 024403. , PRBMDO 0163-1829 10.1103/PhysRevB.72.024403Von Ranke, P.J., De Oliveira, I.G., Guimarães, A.P., Da Silva, X.A., (2000) Phys. Rev. B, 61, p. 447. , PRBMDO 0163-1829 10.1103/PhysRevB.61.447Bak, P., (1974) J. Phys. C, 7, p. 4097. , JPSOAW 0022-3719 10.1088/0022-3719/7/22/014Hutchings., M.T., (1964) Solid State Phys., 16, p. 227. , SSPHAE 0081-1947Lea, K.R., Leask, M.J.M., Wolf, W.P., (1962) J. Phys. Chem. Solids, 33, p. 1381. , JPCSAW 0022-3697Stevens, K.W.H., (1952) Proc. Phys. Soc., London, Sect. a, 65, p. 209. , PPSAAM 0370-1298 10.1088/0370-1298/65/3/308Purwins, H.G., Leson, A., (1990) Adv. Phys., 39, p. 309. , ADPHAH 0001-8732 10.1080/00018739000101511Kuz'Min, M.D., Tishin, A.M., (1991) J. Phys. D, 24, p. 2039. , JPAPBE 0022-3727 10.1088/0022-3727/24/11/02

Asymptotically Improved Convergence of Optimized Perturbation Theory in the Bose-Einstein Condensation Problem

We investigate the convergence properties of optimized perturbation theory, or linear $\delta$ expansion (LDE), within the context of finite temperature phase transitions. Our results prove the reliability of these methods, recently employed in the determination of the critical temperature T_c for a system of weakly interacting homogeneous dilute Bose gas. We carry out the explicit LDE optimized calculations and also the infrared analysis of the relevant quantities involved in the determination of $T_c$ in the large-N limit, when the relevant effective static action describing the system is extended to O(N) symmetry. Then, using an efficient resummation method, we show how the LDE can exactly reproduce the known large-N result for $T_c$ already at the first non-trivial order. Next, we consider the finite N=2 case where, using similar resummation techniques, we improve the analytical results for the nonperturbative terms involved in the expression for the critical temperature allowing comparison with recent Monte Carlo estimates of them. To illustrate the method we have considered a simple geometric series showing how the procedure as a whole works consistently in a general case.Comment: 38 pages, 3 eps figures, Revtex4. Final version in press Phys. Rev.

Exploring the genomic diversity of black yeasts and relatives (Chaetothyriales, Ascomycota)

The order Chaetothyriales (Pezizomycotina, Ascomycetes) harbours obligatorily melanised fungi and includes numerous etiologic agents of chromoblastomycosis, phaeohyphomycosis and other diseases of vertebrate hosts. Diseases range from mild cutaneous to fatal cerebral or disseminated infections and affect humans and cold-blooded animals globally. In addition, Chaetothyriales comprise species with aquatic, rock-inhabiting, ant-associated, and mycoparasitic life-styles, as well as species that tolerate toxic compounds, suggesting a high degree of versatile extremotolerance. To understand their biology and divergent niche occupation, we sequenced and annotated a set of 23 genomes of main the human opportunists within the Chaetothyriales as well as related environmental species. Our analyses included fungi with diverse life-styles, namely opportunistic pathogens and closely related saprobes, to identify genomic adaptations related to pathogenesis. Furthermore, ecological preferences of Chaetothyriales were analysed, in conjuncture with the order-level phylogeny based on conserved ribosomal genes. General characteristics, phylogenomic relationships, transposable elements, sex-related genes, protein family evolution, genes related to protein degradation (MEROPS), carbohydrate-active enzymes (CAZymes), melanin synthesis and secondary metabolism were investigated and compared between species. Genome assemblies varied from 25.81 Mb (Capronia coronata) to 43.03 Mb (Cladophialophora immunda). The bantiana-clade contained the highest number of predicted genes (12,817 on average) as well as larger genomes. We found a low content of mobile elements, with DNA transposons from Tc1/Mariner superfamily being the most abundant across analysed species. Additionally, we identified a reduction of carbohydrate degrading enzymes, specifically many of the Glycosyl Hydrolase (GH) class, while most of the Pectin Lyase (PL) genes were lost in etiological agents of chromoblastomycosis and phaeohyphomycosis. An expansion was found in protein degrading peptidase enzyme families S12 (serine-type D-Ala-D-Ala carboxypeptidases) and M38 (isoaspartyl dipeptidases). Based on genomic information, a wide range of abilities of melanin biosynthesis was revealed; genes related to metabolically distinct DHN, DOPA and pyomelanin pathways were identified. The MAT (MAting Type) locus and other sex-related genes were recognized in all 23 black fungi. Members of the asexual genera Fonsecaea and Cladophialophora appear to be heterothallic with a single copy of either MAT-1-1 or MAT-1-2 in each individual. All Capronia species are homothallic as both MAT1-1 and MAT 1-2 genes were found in each single genome. The genomic synteny of the MAT-locus flanking genes (SLA2-APN2-COX13) is not conserved in black fungi as is commonly observed in Eurotiomycetes, indicating a unique genomic context for MAT in those species. The heterokaryon (het) genes expansion associated with the low selective pressure at the MAT-locus suggests that a parasexual cycle may play an important role in generating diversity among those fungi

Higher Order Evaluation of the Critical Temperature for Interacting Homogeneous Dilute Bose Gases

We use the nonperturbative linear \delta expansion method to evaluate analytically the coefficients c_1 and c_2^{\prime \prime} which appear in the expansion for the transition temperature for a dilute, homogeneous, three dimensional Bose gas given by T_c= T_0 \{1 + c_1 a n^{1/3} + [ c_2^{\prime} \ln(a n^{1/3}) +c_2^{\prime \prime} ] a^2 n^{2/3} + {\cal O} (a^3 n)\}, where T_0 is the result for an ideal gas, a is the s-wave scattering length and n is the number density. In a previous work the same method has been used to evaluate c_1 to order-\delta^2 with the result c_1= 3.06. Here, we push the calculation to the next two orders obtaining c_1=2.45 at order-\delta^3 and c_1=1.48 at order-\delta^4. Analysing the topology of the graphs involved we discuss how our results relate to other nonperturbative analytical methods such as the self-consistent resummation and the 1/N approximations. At the same orders we obtain c_2^{\prime\prime}=101.4, c_2^{\prime \prime}=98.2 and c_2^{\prime \prime}=82.9. Our analytical results seem to support the recent Monte Carlo estimates c_1=1.32 \pm 0.02 and c_2^{\prime \prime}= 75.7 \pm 0.4.Comment: 29 pages, 3 eps figures. Minor changes, one reference added. Version in press Physical Review A (2002

BEC Collapse and Dynamical Squeezing of Vacuum Fluctuations

We analyze the phenomena of Bose Novae, as described by Donley et al [Nature 412, 295 (2001)], by focusing on the behavior of excitations or fluctuations above the condensate, as driven by the dynamics of the condensate (rather than the dynamics of the condensate alone or the kinetics of the atoms). The dynamics of the condensate squeezes and amplifies the quantum excitations, mixing the positive and negative frequency components of their wave functions thereby creating particles which appear as bursts and jets. By analyzing the changing amplitude and particle content of these excitations, our simple physical picture (based on a test field approximation) explains well the overall features of the Bose Novae phenomena and provide excellent quantitative fits with experimental data on several aspects, such as the scaling behavior of the collapse time and the amount of particles in the jet. The predictions of the bursts at this level of approximation is less than satisfactory but may be improved on by including the backreaction of the excitations on the condensate. The mechanism behind the dominant effect -- parametric amplification of vacuum fluctuations and freezing of modes outside of horizon -- is similar to that of cosmological particle creation and structure formation in a rapid quench (which is fundamentally different from Hawking radiation in black holes). This shows that BEC dynamics is a promising venue for doing `laboratory cosmology'.Comment: Latex 36 pages, 6 figure