Non-Gaussianity of Racetrack Inflation Models

In this paper, we use the result in [C.Y. Sun and D.H. Zhang, arXivastro-ph/0510709] to calculate the non-Gaussianity of the racetrack models in[J.J. Blanco-Pillado, et al., JHEP 0411 (2004) 063; arXivhep-th/0406230]and [J.J. Blanco-Pillado, et al., arXivhep-th/0603129]. The two models give different non-Gaussianities. Both of them are reasonable. However, we find that, for multi-field inflationary models with the non-trivial metric of the field space,the condition of the slow-roll cannot guarantee small non-Gaussianities.     

Comments on ultra-high-energy photons and D-foam models

We revisit the constraints that the non-observation of ultra-high-energy photons due to the GZK cutoff can impose on models of Lorentz violation in photon propagation, following recent work by Maccione, Liberati and Sigl (2010) [arXiv:1003.5468] that carries further an earlier analysis by the present authors [J. Ellis et al., Phys. Rev. D 63 (2001) 12402, hep-th/0012216]. We argue that the GZK cutoff constraint is naturally evaded in the D-brane model of space–time foam presented recently by the present authors [J. Ellis et al., Phys. Lett. B 665 (2008) 412, arXiv:0804.3566], in which Lorentz-violating effects on photon propagation are independent of possible effects during interactions. We also note a novel absorption mechanism that could provide a GZK-like cutoff for photons in low-scale string models.     

Geometric counter-vertex for open string scattering on D-branes

In arXiv:0801.0218 [hep-th] it was conjectured that quantum effects of open strings moving on D-branes generate the D-brane geometry through a counter-vertex operator. The conjecture has been checked at one-loop in arXiv:0806.3330 [hep-th]. Here we discuss the two-loop extension.     

Quantum gravity, minimum length and Keplerian orbits

We conjecture that the modified commutation relations suggested in the context of quantum gravity (QG) persist also in the classical limit, if the momentum of the classical object is not too large, and calculate the corresponding perihelion precession rate for Keplerian orbits. The main result obtained in this Letter is not new. However the derivation is much simpler than the one proposed by Benczik et al. in [S. Benczik, L.N. Chang, D. Minic, N. Okamura, S. Rayyan, T. Takeuchi, Phys. Rev. D 66 (2002) 026003, arXiv:hep-th/0204049] where the corresponding precession rate was calculated for the first time. Our interpretation of the result is also quite different.     

Note on quantum groups and integrable systems

The free-field formalism for quantum groups [preprint ITEP-M3/94, CRM-2202 hep-th/9409093] provides a special choice of coordinates on a quantum group. In these coordinates the construction of associated integrable system [arXiv:1207.1869] is especially simple. This choice also fits into general framework of cluster varieties [math.AG/0311245]—natural changes in coordinates are cluster mutations.     

Small amplitude forced fluid dynamics from gravity at T=0

The usual derivative expansion of gravity duals of charged fluid dynamics is known to break down in the zero temperature limit. In this case, fluid–gravity duality is not understood precisely. We explore this problem for a zero temperature charged fluid driven by a low frequency, small amplitude and spatially homogeneous external force. In the gravity dual, this corresponds to a time dependent boundary value of the dilaton. We calculate the bulk solution for the dilaton and the leading back reaction to the metric and the gauge fields using the modified low frequency expansion of Faulkner et al. (arXiv:0907.2694 [hep-th]). The resulting solutions are regular everywhere, establishing fluid–gravity duality to this order.     

2PI functional techniques for abelian gauge theories

We summarize our recent work [U. Reinosa, J. Serreau, JHEP 0711 (2007) 097 [arXiv:0708.0971 [hep-th]]; U. Reinosa, J. Serreau, JHEP 0607 (2006) 028; See also Nucl. Phys. A 785 (2007) 230; U. Reinosa, J. Serreau, in preparation] concerning the formulation of two-particle-irreducible (2PI) functional techniques for abelian gauge field theories.     

Localization of matter and fermion resonances on double walls

We investigate the possibility of localizing various matter fields on the double walls. For spin 0 scalar field, massless zero mode can be normalized on the double walls. However, for spin 1 vector field, the zero mode is not localized on the double walls. In the paper [C.A.S. Almeida, M.M. Ferreira Jr., A.R. Gomes, R. Casana, arXiv:0901.3543 [hep-th]], the authors investigated fermion localization on a Bloch brane, especially, they found fermion resonances on the Bloch brane for both chiralities and related their appearance to branes with internal structure. Inspired by their work, for spin 1/2 spinor field, we focus our attention mainly on the fermion resonances, and also found fermion resonances for both left-handed fermions and right-handed ones on the double walls, which further supports the arguments presented in the paper [C.A.S. Almeida, M.M. Ferreira Jr., A.R. Gomes, R. Casana, arXiv:0901.3543 [hep-th]].     

Cosmic acceleration and crossing of in non-minimal modified Gauss–Bonnet gravity

Modified Gauss–Bonnet, i.e., f(G) gravity is a possible explanation of dark energy. Late time cosmology for the f(G) gravity non-minimally coupled with a free massless scalar field have been investigated in Ref. [S. Nojiri, S.D. Odintsov, P.V. Tretyakov, Phys. Lett. B 651 (2007) 224, arXiv:0704.2520 [hep-th]; S. Nojiri, S.D. Odintsov, P.V. Tretyakov, Progr. Theor. Phys. Suppl. 172 (2008) 81, arXiv:0710.5232]. In this Letter we generalize the work of Ref. [S. Nojiri, S.D. Odintsov, P.V. Tretyakov, Phys. Lett. B 651 (2007) 224, arXiv:0704.2520 [hep-th]; S. Nojiri, S.D. Odintsov, P.V. Tretyakov, Progr. Theor. Phys. Suppl. 172 (2008) 81, arXiv:0710.5232] by including scalar potential in the matter Lagrangian which is non-minimally coupled with modified Gauss–Bonnet gravity. Also we obtain the conditions for having a much more amazing problem than the acceleration of the universe, i.e. crossing of ω=−1, in f(G) non-minimally coupled with tachyonic Lagrangian.     

A new recursion operator for Adler?s equation in the Viallet form

For Adler?s equation in the Viallet form and Yamilov?s discretisation of the Krichever-Novikov equation we present new recursion and Hamiltonian operators. This new recursion operator and the recursion operator found in [A.V. Mikhailov, et al., Theor. Math. Phys. 167 (2011) 421, arXiv:1004.5346] satisfy the spectral curve associated with the equation.     

Angular Distributions for

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Moduli stabilization, large-volume dS minimum without -branes, (non-)supersymmetric black hole attractors and two-parameter Swiss cheese Calabi–Yau's

We consider two sets of issues in this paper. The first has to do with moduli stabilization, existence of “area codes” [A. Giryavets, New attractors and area codes, JHEP 0603 (2006) 020, hep-th/0511215] and the possibility of getting a non-supersymmetric dS minimum without the addition of -branes as in KKLT for type II flux compactifications. The second has to do with the “inverse problem” [K. Saraikin, C. Vafa, Non-supersymmetric black holes and topological strings, hep-th/0703214] and “fake superpotentials” [A. Ceresole, G. Dall'Agata, Flow equations for non-BPS extremal black holes, JHEP 0703 (2007) 110, hep-th/0702088] for extremal (non-)supersymmetric black holes in type II compactifications. We use (orientifold of) a “Swiss cheese” Calabi–Yau [J.P. Conlon, F. Quevedo, K. Suruliz, Large-volume flux compactifications: Moduli spectrum and D3/D7 soft supersymmetry breaking, JHEP 0508 (2005) 007, hep-th/0505076] expressed as a degree-18 hypersurface in WCP⁴[1,1,1,6,9] in the “large-volume-scenario” limit [V. Balasubramanian, P. Berglund, J.P. Conlon, F. Quevedo, Systematics of moduli stabilisation in Calabi–Yau flux compactifications, JHEP 0503 (2005) 007, hep-th/0502058]. The main result of our paper is that we show that by including non-perturbative α^′ and instanton corrections in the Kähler potential and superpotential [T.W. Grimm, Non-perturbative corrections and modularity in N=1 type IIB compactifications, arXiv: 0705.3253 [hep-th]], it may be possible to obtain a large-volume non-supersymmetric dS minimum without the addition of anti-D3 branes a la KKLT. The chosen Calabi–Yau has been of relevance also from the point of other studies of Kähler moduli stabilization via non-perturbative instanton contributions [F. Denef, M.R. Douglas, B. Florea, Building a better racetrack, JHEP 0406 (2004) 034, hep-th/0404257] and non-supersymmetric AdS vacua (and their subsequent dS-uplifts) using (α^′)³ corrections to the Kähler potential [V. Balasubramanian, P. Berglund, J.P. Conlon, F. Quevedo, Systematics of moduli stabilisation in Calabi–Yau flux compactifications, JHEP 0503 (2005) 007, hep-th/0502058; K. Becker, M. Becker, M. Haack, J. Louis, Supersymmetry breaking and alpha'-corrections to flux induced potentials, JHEP 0206 (2002) 060, hep-th/0204254; A. Westphal, de Sitter string vacua from Kähler uplifting, JHEP 0703 (2007) 102, hep-th/0611332; V. Balasubramanian, P. Berglund, Stringy corrections to Kähler potentials, SUSY breaking, and the cosmological constant problem, JHEP 0411 (2004) 085, hep-th/0408054].     

Extremal Kerr black hole/CFT correspondence in the five-dimensional Gödel universe

We extend the method of Kerr/CFT correspondence recently proposed in arXiv:0809.4266 [hep-th] to the extremal (charged) Kerr black hole embedded in the five-dimensional Gödel universe. With the aid of the central charges in the Virasoro algebra and the Frolov–Thorne temperatures, together with the use of the Cardy formula, we have obtained the microscopic entropies that precisely agree with the ones macroscopically calculated by Bekenstein–Hawking area law.     

Quantum Stabilization of Moduli in a Slice of AdS6 Compactified on S 1

We review the effective potential due to massive bulk scalar fields in higher-dimensional warped brane models found in Flachi et al. (Quantum stabilization of moduli in higher dimensional brane models, arXiv:hep-th/0301, 2003) specializing it to a slice of AdS₆ compactified on the circle. This model contains two moduli that parametrize the interbrane distance and the size of S ¹, or equivalently the positions of the two branes. Their values determine the Planck/EW hierarchy, in a combination of large volume and redshift effects. It is found that the observed hierarchy is compatible with both moduli stabilized by the Casimir forces without fine-tuning (except for the one needed to match the cosmological constant). This contrasts with the Randall—Sundrum model, where gauge fields in the bulk are needed.     

Higher-spin gauge and trace anomalies in two-dimensional backgrounds

Two-dimensional quantum fields in electric and gravitational backgrounds can be described by conformal field theories, and hence all the physical (covariant) quantities can be written in terms of the corresponding holomorphic quantities. In this paper, we first derive relations between covariant and holomorphic forms of higher-spin currents in these backgrounds, and then, by using these relations, obtain higher-spin generalizations of the trace and gauge (or gravitational) anomalies up to spin 4. These results are applied to derive higher-moments of Hawking fluxes in black holes in a separate paper [S. Iso, T. Morita, H. Umetsu, Hawking radiation via higher-spin gauge anomalies, arXiv: 0710.0456 [hep-th]].     

Deformation quantization of fermi fields

Deformation quantization for any Grassmann scalar free field is described via the Weyl-Wigner-Moyal formalism. The Stratonovich-Weyl quantizer, the Moyal -product and the Wigner functional are obtained by extending the formalism proposed recently in [I. Galaviz, H. García-Compeán, M. Przanowski, F.J. Turrubiates, Weyl-Wigner-Moyal Formalism for Fermi Classical Systems, arXiv:hep-th/0612245] to the fermionic systems of infinite number of degrees of freedom. In particular, this formalism is applied to quantize the Dirac free field. It is observed that the use of suitable oscillator variables facilitates considerably the procedure. The Stratonovich-Weyl quantizer, the Moyal -product, the Wigner functional, the normal ordering operator, and finally, the Dirac propagator have been found with the use of these variables.     

Exact Spectrum of Anomalous Dimensions of Planar <Emphasis Type="Italic">N</Emphasis> = 4 Supersymmetric Yang–Mills Theory: TBA and excited states

Using the thermodynamic Bethe ansatz method we derive an infinite set of integral non-linear equations for the spectrum of states/operators in AdS/CFT. The Y-system conjectured in Gromov et al. (Integrability for the Full Spectrum of Planar AdS/CFT. arXiv:0901.3753 [hep-th]) for the spectrum of all operators in planar N = 4 SYM theory follows from these equations. In particular, we present the integral TBA type equations for the spectrum of all operators within the sl(2) sector. We prove that all the kernels and free terms entering these TBA equations are real and have nice fusion properties in the relevant mirror kinematics. We find the analog of DHM formula for the dressing kernel in the mirror kinematics.     

Hawking radiation,effective actions and covariant boundary conditions

From an appropriate expression for the effective action, the Hawking radiation from charged black holes is derived, using only covariant boundary conditions at the event horizon. The connection of our approach with the Unruh vacuum and the recent analysis [S.P. Robinson, F. Wilczek, Phys. Rev. Lett. 95 (2005) 011303, gr-qc/0502074; S. Iso, H. Umetsu, F. Wilczek, Phys. Rev. Lett. 96 (2006) 151302, hep-th/0602146; R. Banerjee, S. Kulkarni, arXiv: 0707.2449 [hep-th]] of Hawking radiation using anomalies is established.     

A new continuum limit of matrix models

We define a new scaling limit of matrix models which can be related to the method of causal dynamical triangulations (CDT) used when investigating two-dimensional quantum gravity. Surprisingly, the new scaling limit of the matrix models is also a matrix model, thus explaining why the recently developed CDT continuum string field theory [J. Ambjørn, R. Loll, Y. Watabiki, W. Westra, S. Zohren, arXiv: 0802.0719] has a matrix-model representation [J. Ambjørn, R. Loll, Y. Watabiki, W. Westra, S. Zohren, arXiv: 0804.0252].     

Reexamining the security of the improved quantum secret sharing scheme

We find that, in the improvement [S.J. Qin et al., Phys. Lett. A 357 (2006) 101] of the multiparty quantum secret sharing [Z.J. Zhang et al., Phys. Rev. A 71 (2005) 044301], Charlie can solely obtain Alice’s secret messages without Bob’s helps. In other words, the improved secret sharing scheme is still insecure. In the end, we further modify Qin et al. improved three-party quantum secret sharing scheme and make it really secure.