Partition Functions of Pure Spinors

We compute partition functions describing multiplicities and charges of massless and first massive string states of pure-spinor superstrings in 3,4,6,10 dimensions. At the massless level we find a spin-one gauge multiplet of minimal supersymmetry in d dimensions. At the first massive string level we find a massive spin-two multiplet. The result is confirmed by a direct analysis of the BRST cohomology at ghost number one. The central charges of the pure spinor systems are derived in a manifestly SO(d) covariant way confirming that the resulting string theories are critical. A critical string model with N=(2,0) supersymmetry in d=2 is also described.Comment: LaTex, 30 p

Wilson Loops and Chiral Correlators on Squashed Sphere

We study chiral deformations of ${\cal N}=2$ and ${\cal N}=4$ supersymmetric gauge theories obtained by turning on $\tau_J \,{\rm tr} \, \Phi^J$ interactions with $\Phi$ the ${\cal N}=2$ superfield. Using localization, we compute the deformed gauge theory partition function $Z(\vec\tau|q)$ and the expectation value of circular Wilson loops $W$ on a squashed four-sphere. In the case of the deformed ${\cal N}=4$ theory, exact formulas for $Z$ and $W$ are derived in terms of an underlying $U(N)$ interacting matrix model replacing the free Gaussian model describing the ${\cal N}=4$ theory. Using the AGT correspondence, the $\tau_J$-deformations are related to the insertions of commuting integrals of motion in the four-point CFT correlator and chiral correlators are expressed as $\tau$-derivatives of the gauge theory partition function on a finite $\Omega$-background. In the so called Nekrasov-Shatashvili limit, the entire ring of chiral relations is extracted from the $\epsilon$-deformed Seiberg-Witten curve. As a byproduct of our analysis we show that $SU(2)$ gauge theories on rational $\Omega$-backgrounds are dual to CFT minimal models.Comment: 33 pages, 2 figure, in this version we have added two new references and a detailed comparison with the results obtained in one of these tw

The Fundamental Multi-Baseline Mode-Mixing Foreground in 21 cm EoR Observations

The primary challenge for experiments measuring the neutral hydrogen power spectrum from the Epoch of Reionization (EoR) are mode-mixing effects where foregrounds from very bright astrophysical sources interact with the instrument to contaminate the EoR signal. In this paper we identify a new type of mode-mixing that occurs when measurements from non-identical baselines are combined for increased power spectrum sensitivity. This multi-baseline effect dominates the mode-mixing power in our simulations and can contaminate the EoR window, an area in Fourier space previously identified to be relatively free of foreground power.Comment: Submitted to Ap

On the perturbative corrections around D-string instantons

We study ${\cal F}^4$-threshold corrections in an eight dimensional S-dual pair of string theories, as a prototype of dual string vacua with sixteen supercharges. We show that the orbifold CFT description of D-string instantons gives rise to a perturbative expansion similar to the one appearing on the fundamental string side. By an explicit calculation, using the Nambu-Goto action in the static gauge, we show that the first subleading term agrees precisely on the two sides. We then give a general argument to show that the agreement extends to all orders.Comment: 12 page

Dynamical Supersymmetry Breaking in Intersecting Brane Models

In this paper we study dynamical supersymmetry breaking in absence of gravity with the matter content of the minimal supersymmetric standard model. The hidden sector of the theory is a strongly coupled gauge theory, realized in terms of microscopic variables which condensate to form mesons. The supersymmetry breaking scalar potential combines F, D terms with instanton generated interactions in the Higgs-mesons sector. We show that for a large region in parameter space the vacuum breaks in addition to supersymmetry also electroweak gauge symmetry. We furthermore present local D-brane configurations that realize these supersymmetry breaking patterns.Comment: 30 pages, 4 figures, pdflate

Probing Fuzzballs with Particles, Waves and Strings

We probe D1D5 micro-state geometries with massless particles, waves and strings. To this end, we study geodetic motion, Klein-Gordon equation and string scattering in the resulting gravitational background. Due to the reduced rotational symmetry, even in the simple case of a circular fuzzball, the system cannot be integrated elementarily. Yet, for motion in the plane of the string profile or in the orthogonal plane to it, one can compute the deflection angle or the phase shift and identify the critical impact parameter, at which even a massless probe is captured by the fuzzball if its internal momentum is properly tuned. We find agreement among the three approaches, thus giving further support to the fuzzball proposal at the dynamical level.Comment: 35 pages. Extended and improved discussions on the integrability of the geodetic equations and on the critical impact parameter

AdS/CFT correspondence and D1/D5 systems in theories with 16 supercharges

We discuss spectra of $AdS_3$ supergravities, arising in the near horizon geometry of D1/D5 systems in orbifolds/orientifolds of type IIB theory with 16 supercharges. These include models studied in a recent paper (hep-th/0012118), where the group action involves also a shift along a transversal circle, as well as IIB/$\Omega I_4$, which is dual to IIB on $K3$. After appropriate assignements of the orbifold group eigenvalues and degrees to the supergravity single particle spectrum, we compute the supergravity elliptic genus and find agreement, in the expected regime of validity, with the elliptic genus obtained using U-duality map from (4,4) CFTs of U-dual backgrounds. Since this U-duality involves the exchange of KK momentum $P$ and D1 charge $N$, it allows us to test the (4,4) CFTs in the $P < N/4$ and $N < P/4$ regimes by two different supergravity duals.Comment: 28 pages, no figure

Photospheric activity, rotation and magnetic interaction in LHS 6343 A

Context. The Kepler mission has recently discovered a brown dwarf companion transiting one member of the M4V+M5V visual binary system LHS 6343 AB with an orbital period of 12.71 days. Aims. The particular interest of this transiting system lies in the synchronicity between the transits of the brown dwarf C component and the main modulation observed in the light curve, which is assumed to be caused by rotating starspots on the A component. We model the activity of this star by deriving maps of the active regions that allow us to study stellar rotation and the possible interaction with the brown dwarf companion. Methods. An average transit profile was derived, and the photometric perturbations due to spots occulted during transits are removed to derive more precise transit parameters. We applied a maximum entropy spot model to fit the out-of-transit optical modulation as observed by Kepler during an uninterrupted interval of 500 days. It assumes that stellar active regions consist of cool spots and bright faculae whose visibility is modulated by stellar rotation. Results. Thanks to the extended photometric time series, we refine the determination of the transit parameters and find evidence of spots that are occulted by the brown dwarf during its transits. The modelling of the out-of-transit light curve of LHS 6343 A reveals several starspots rotating with a slightly longer period than the orbital period of the brown dwarf, i.e., 13.13 +- 0.02 days. No signature attributable to differential rotation is observed. We find evidence of a persistent active longitude on the M dwarf preceding the sub- companion point by 100 deg and lasting for at least 500 days. This can be relevant for understanding how magnetic interaction works in low-mass binary and star-planet systems.Comment: 14 pages, 16 figure