We discuss the existence of glueball states for N =1 SYM within the Maldacena-Núñez model. We find that for this model the existence of an area law in the Wilson loop operator does not imply the existence of a discrete glueball spectrum. We suggest that implementing the model with an upper hard cut-off can amend the lack of spectrum. As a result the model can be only interpreted in the infra-red region. A direct comparison with the lattice data allows us to fix the scale up to where the model is sensible to describe low-energy observables. Nevertheless, taking for granted the lattice results, the resulting spectrum does not follow the general trends found in other supergravity backgrounds. We further discuss the decoupling of the non-singlet Kaluza-Klein states by analysing the associated supergravity equation of motion. The inclusion of non-commutative effects is also analysed and we find that leads to an enhancement on the value of the masses.

The electrical conductivity of two-dimensional (2D) materials without any electrical contact can be obtained using two different methods: the terahertz time domain spectroscopy (THz-TDS) method, in the range from GHz up to 2 THz, and with a rutile dielectric resonator (RDR), in which case the conductivity is obtained at the resonant frequency of the device, close to 9.0 GHz. In one case (THz-TDS in a transmission setup), the sample is directly focused. In the other case (RDR), the sample is placed inside the resonant cavity working at TE 011 mode and must have exactly the same surface size as the cavity, 12 Â 12 mm in our device. From the Q factor variation of the resonant cavity due to the sample, its surface resistance is extracted. These measurements are performed on different 2D materials: graphene and WS 2. Both methods are analyzed and compared. For few-layer 2D samples, the THz-TDS method is suitable.

Measuring the electrical surface resistance of 2D materials without contact can provide a method for obtaining their intrinsic characterization. Herein, the aim is to show that a rutile dielectric resonator (RDR) can be used to measure the electrical surface resistance of conducting coatings deposited on substrates, at the resonance frequency. Moreover, it is known that the substrate exerts a strong influence capable of intrinsically modify the properties of 2D materials, as found in graphene. The RDR method is used for different samples of metals (Cu, Mo, Ti, and brass), carbon nanotubes (bucky paper), a film of compacted graphene flakes, a film of compacted graphene oxide flakes, and graphene obtained by chemical vapor deposition (CVD) on different substrates (SiO2/Si, quartz, and polyethylene terephthalate [PET]). The results show that reasonable values can be obtained for thin conducting materials with a thickness of not less than a few micrometers. In the case of graphene grown on a substrate, the presence of graphene is clearly detected but the resistivity value cannot be extracted.

The sentence in between eqs. (2.16) and (2.17) should read: Ψ R transforms under T-parity.

Speaker. † Work supported in part by MCYT under contract FPA2003-09298-C02-01 and by Junta de Andalucía group FQM 101 and by MIUR under contract 2004021808_009.