5D Yang-Mills instantons from ABJM Monopoles

In the presence of a background supergravity flux, N M2-branes will expand via the Myers effect into M5-branes wrapped on a fuzzy three-sphere. In previous work the fluctuations of the M2-branes were shown to be described by the five-dimensional Yang-Mills gauge theory associated to D4-branes. We show that the ABJM prescription for eleven-dimensional momentum in terms of magnetic flux lifts to an instanton flux of the effective five-dimensional Yang-Mills theory on the sphere, giving an M-theory interpretation for these instantons.Comment: 29 pages, Latex; v2: added references and a comment on the graviphoton coupling in section 5; v3: typos corrected and references adde

Correspondence principle for a brane in Minkowski space and vector mesons

We consider a 3-brane of positive cosmological constant (de Sitter) in D-dimensional Minkowski space. We show that the Poincare algebra in the bulk yields a SO(4,2) algebra when restricted to the brane. In the limit of zero cosmological constant (flat brane), this algebra turns into the conformal algebra on the brane. We derive a correspondence principle for Minkowski space analogous to the AdS/CFT correspondence. We discuss explicitly the cases of scalar and gravitational fields. For a 3-brane of finite thickness in the transverse directions, we obtain a spectrum for vector gravitational perturbations which correspond to vector mesons. The spectrum agrees with the one obtained in truncated AdS space by de Teramond and Brodsky provided D=10 and the bulk mass scale M is of order the geometric mean of the Planck mass ($\bar M$) on the brane and $\Lambda_{QCD}$ ($M \sim (\bar M \Lambda_{QCD})^{1/2} \sim 10^9$ GeV).Comment: 8 pages in two-column ReVTeX

Quark-Gluon Plasma/Black Hole duality from Gauge/Gravity Correspondence

The Quark-Gluon Plasma (QGP) is the QCD phase of matter expected to be formed at small proper-times in the collision of heavy-ions at high energy. Experimental observations seem to favor a strongly coupled QCD plasma with the hydrodynamic properties of a quasi-perfect fluid, i.e. rapid thermalization (or isotropization) and small viscosity. The theoretical investigation of such properties is not obvious, due to the the strong coupling. The Gauge/Gravity correspondence provides a stimulating framework to explore the strong coupling regime of gauge theories using the dual string description. After a brief introduction to Gauge/Gravity duality, and among various existing studies, we focus on challenging problems of QGP hydrodynamics, such as viscosity and thermalization, in terms of gravitational duals of both the static and relativistically evolving plasma. We show how a Black Hole geometry arises naturally from the dual properties of a nearly perfect fluid and explore the lessons and prospects one may draw for actual heavy ion collisions from the Gauge/Gravity duality approach.Comment: 6 pages, 4 figures, invited talk at the EPS HEP 2007 Conference, Manchester (UK), and at the ``Deuxiemes rencontres PQG-France'', Etretat (2007); reference adde

A Trouble with Ho\v{r}ava-Lifshitz Gravity

We study the structure of the phase space in Ho\v{r}ava-Lifshitz theory. With the constraints derived from the action, the phase space is described by five fields, thus there is a lack of canonical structure. The Poisson brackets of the Hamiltonian density do not form a closed structure, resulting in many new constraints. Taking these new constraints into account, it appears that there is no degree of freedom left, or the phase space is reduced to one with an odd number of fields.Comment: 12 pages, some discussions, comments and references added, JHEP styl

Methanol loading dependent methoxylation in zeolite H-ZSM-5

We evaluate the effect of the number of methanol molecules per acidic site of H-ZSM-5 on the methoxylation reaction at room temperature by applying operando diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS) and mass spectrometry (MS), which capture the methoxylation reaction by simultaneously probing surface adsorbed species and reaction products, respectively. To this end, the methanol loading in H-ZSM-5 (Si/Al ≈ 25) pores is systematically varied between 32, 16, 8 and 4 molecules per unit cell, which corresponds to 8, 4, 2 and 1 molecules per Brønsted acidic site, respectively. The operando DRIFTS/MS data show that the room temperature methoxylation depends on the methanol loading: the higher the methanol loading, the faster the methoxylation. Accordingly, the reaction is more than an order of magnitude faster with 8 methanol molecules per Brønsted acidic site than that with 2 molecules, as evident from the evolution of the methyl rock band of the methoxy species and of water as a function of time. Significantly, no methoxylation is observed with ≤1 molecule per Brønsted acidic site. However, hydrogen bonded methanol occurs across all loadings studied, but the structure of hydrogen bonded methanol also depends on the loading. Methanol loading of ≤1 molecule per acidic site leads to the formation of hydrogen bonded methanol with no proton transfer (i.e. neutral geometry), while loading ≥2 molecules per acidic site results in a hydrogen bonded methanol with a net positive charge on the adduct (protonated geometry). The infrared vibrational frequencies of methoxy and hydrogen bonded methanol are corroborated by Density Functional Theory (DFT) calculations. Both the experiments and calculations reflect the methoxy bands at around 940, 1180, 2868–2876 and 2980–2973 cm−1 which correspond to ν(C–O), ρ(CH3), νs(C–H) and νas(C–H), respectively

Eliminating ambiguities for quantum corrections to strings moving in AdS4×CP3AdS_4\times \mathbb{CP}^3

We apply a physical principle, previously used to eliminate ambiguities in quantum corrections to the 2 dimensional kink, to the case of spinning strings moving in $AdS_4\times \mathbb{CP}^3$, thought of as another kind of two dimensional soliton. We find that this eliminates the ambiguities and selects the result compatible with AdS/CFT, providing a solid foundation for one of the previous calculations, which found agreement. The method can be applied to other classical string "solitons".Comment: 18 pages, latex; references added, comments added at end of section 4, a few words changed; footnote added on page 1

Neural Responses to Naturalistic Clips of Behaving Animals Under Two Different Task Contexts

The human brain rapidly deploys semantic information during perception to facilitate our interaction with the world. These semantic representations are encoded in the activity of distributed populations of neurons (Haxby et al., 2001; McClelland and Rogers, 2003; Kriegeskorte et al., 2008b) and command widespread cortical real estate (Binder et al., 2009; Huth et al., 2012). The neural representation of a stimulus can be described as a location (i.e., response vector) in a high-dimensional neural representational space (Kriegeskorte and Kievit, 2013; Haxby et al., 2014). This resonates with behavioral and theoretical work describing mental representations of objects and actions as being organized in a multidimensional psychological space (Attneave, 1950; Shepard, 1958, 1987; Edelman, 1998; Gärdenfors and Warglien, 2012). Current applications of this framework to neural representation (e.g., Kriegeskorte et al., 2008b) often implicitly assume that these neural representational spaces are relatively fixed and context-invariant. In contrast, earlier work emphasized the importance of attention and task demands in actively reshaping representational space (Shepard, 1964; Tversky, 1977; Nosofsky, 1986; Kruschke, 1992). A growing body of work in both electrophysiology (e.g., Sigala and Logothetis, 2002; Sigala, 2004; Cohen and Maunsell, 2009; Reynolds and Heeger, 2009) and human neuroimaging (e.g., Hon et al., 2009; Jehee et al., 2011; Brouwer and Heeger, 2013; Çukur et al., 2013; Sprague and Serences, 2013; Harel et al., 2014; Erez and Duncan, 2015; Nastase et al., 2017) has suggested mechanisms by which behavioral goals dynamically alter neural representation

On Non-linear Action for Gauged M2-brane

We propose a non-linear extension of U(1) \times U(1) (abelian) ABJM model including T_{M2} (higher derivative) corrections. The action proposed here is expected to describe a single M2-brane proving C^4/Z_k target space. The model includes couplings with the 3-form background in the eleven-dimensional supergravity which is consistent with the orbifold projection. We show that the novel higgs mechanism proposed by Mukhi and Papageorgakis does work even in the presence of higher derivative corrections and couplings with the background field, giving the correct structure of the Dirac-Born-Infeld action with Wess-Zumino term for a D2-brane. We also find half BPS solutions in the full non-linear theory which is interpreted as an another M2-brane intersecting with the original M2-brane. A possible generalization to U(N) \times U(N) gauge group is briefly discussed.Comment: 19 pages, no figure, references added, typos correcte

Consistent truncation of d = 11 supergravity on AdS_4 x S^7

We study the system of equations derived twenty five years ago by B. de Wit and the first author [Nucl. Phys. B281 (1987) 211] as conditions for the consistent truncation of eleven-dimensional supergravity on AdS_4 x S^7 to gauged N = 8 supergravity in four dimensions. By exploiting the E_7(7) symmetry, we determine the most general solution to this system at each point on the coset space E_7(7)/SU(8). We show that invariants of the general solution are given by the fluxes in eleven-dimensional supergravity. This allows us to both clarify the explicit non-linear ansatze for the fluxes given previously and to fill a gap in the original proof of the consistent truncation. These results are illustrated with several examples.Comment: 41 pages, typos corrected, published versio