118538275
Holographic fermionic fixed points in d=3
We present a top-down string theory holographic model of strongly interacting relativistic 2 + 1-dimensional fermions, paying careful attention to the discrete symmetries of parity and time reversal invariance. Our construction is based on probe D7-branes in AdS5 × S5, stabilized by internal fluxes. We find three solutions, a parity and time reversal invariant conformal field theory which can be viewed as a particular deformation of Coulomb interacting graphene, a parity and time reversal violating but gapless field theory and a system with a parity and time reversal violating charge gap. We show that the Chern-Simons-like electric response function, which is generated perturbatively at one-loop order by parity violating fermions and which is protected by a no-renormalization theorem at orders beyond one loop, indeed appears with the correctly quantized coefficient in the charge gapped theory. In the gapless parity violating solution, the Chern-Simons response function obtains quantum corrections which we compute in the holographic theory.
15932550
String theory effects on five-dimensional black hole physics
We review recent developments in understanding quantum/string corrections to BPS black holes and strings in five-dimensional supergravity. These objects are solutions to the effective action obtained from M-theory compactified on a Calabi–Yau threefold, including the one-loop corrections determined by anomaly cancellation and supersymmetry. We introduce the off-shell formulation of this theory obtained through the conformal supergravity method and review the methods for investigating supersymmetric solutions. This leads to quantum/string corrected attractor geometries, as well as asymptotically flat black strings and spinning black holes. With these solutions in hand, we compare our results with analogous studies in four-dimensional string-corrected supergravity, emphasizing the distinctions between the four- and five-dimensional theories.
18230670
Stringy NJL and Gross-Neveu models at finite density and temperature
Nonlocal stringy versions of the Nambu-Jona-Lasinio and Gross-Neveu models arise in a certain limit of holographic QCD. We analyze the phase structure at finite density and temperature at strong coupling in terms of probe branes in the gravity dual. Comparison with the phase structure of the local field theory models shows qualitative agreement with some aspects, and disagreement with others. Finally, we explain how to construct the Landau potentials for these models by taking the probe branes off-shell.
119206090
Flavor-symmetry breaking with charged probes
A bstractWe discuss the recombination of brane/anti-brane pairs carrying D3 brane charge in AdS5 × S5. These configurations are dual to co-dimension one defects in the $ \mathcal{N} $ = 4 super-Yang-Mills description. Due to their D3 charge, these defects are actually domain walls in the dual gauge theory, interpolating between vacua of different gauge symmetry. A pair of unjoined defects each carry localized (2 + 1) dimensional fermions and possess a global U(N) × U(N) flavor symmetry while the recombined brane/anti-brane pairs exhibit only a diagonal U(N). We study the thermodynamics of this flavor-symmetry breaking under the influence of external magnetic field.
14594667
Moduli space and phase structure of heterotic strings in two dimensions
We explore the moduli space of heterotic strings in two dimensions. In doing so, we introduce new lines of compactified theories with Spin(24) gauge symmetry and discuss compactifications with Wilson lines. The phase structure of $d=2$ heterotic string theory is examined by classifying the hypersurfaces in moduli space which support massless quanta or discrete states. Finally, we compute the torus amplitude over much of the moduli space.
118433665
XENON100 exclusion limit without considering L-eff as a nuisance parameter
In 2011, the XENON100 experiment has set unprecedented constraints on dark matter-nucleon interactions, excluding dark matter candidates with masses down to 6 GeV if the corresponding cross section is larger than 10^{-39} cm^2. The dependence of the exclusion limit in terms of the scintillation efficiency (Leff) has been debated at length. To overcome possible criticisms XENON100 performed an analysis in which Leff was considered as a nuisance parameter and its uncertainties were profiled out by using a Gaussian likelihood in which the mean value corresponds to the best fit Leff value smoothly extrapolated to zero below 3 keVnr. Although such a method seems fairly robust, it does not account for more extreme types of extrapolation nor does it enable to anticipate on how much the exclusion limit would vary if new data were to support a flat behaviour for Leff below 3 keVnr, for example. Yet, such a question is crucial for light dark matter models which are close to the published XENON100 limit. To answer this issue, we use a maximum Likelihood ratio analysis, as done by the XENON100 collaboration, but do not consider Leff as a nuisance parameter. Instead, Leff is obtained directly from the fits to the data. This enables us to define frequentist confidence intervals by marginalising over Leff.
118366559
Searching for GeV-scale new Gauge Bosons in QGP thermal dilepton production
In this paper we propose to use the measurement of the thermal Quark-Gluon Plasma (QGP) dilepton spectra in the Intermediate Mass Region (IMR) of heavy-ion collisions, as a new method to search for GeV-scale dark gauge bosons (gamma' or Z'). Such light mediators are a common feature of light (i.e. low mass) dark matter scenarios, which have been invoked to explain puzzling signals in dark matter indirect and direct detection experiments. First we show that a light gamma' or Z' will generate a resonant enhancement of the dilepton spectrum produced thermally by the QGP, at an energy corresponding to the dark gauge boson mass. Secondly, using data from the PHENIX experiment, we are able to set an upper limit on the combined coupling of this new gauge boson to quarks and leptons (independently of their vectorial or axial nature) chi_q chi_e < 10^(-3) at the 95% confidence level for a gauge boson mass in the range 1.5 - 2.5 GeV. This result complements previous searches for new light gauge bosons and probes a new region of the parameter space, particularly interesting in the case of non-universal couplings to quarks and leptons. Prospects for the discovery of such a boson by the ALICE collaboration are also discussed.