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We make a first study of the phenomenological implications of twisted moduli in type I intersecting D5-brane models, focussing on the resulting predictions at the LHC using SOFTSUSY to estimate the Higgs and sparticle spectra. Twisted moduli can play an important role in giving a viable string realisation of sequestering in the limit where supersymmetry breaking comes entirely from the twisted moduli. We focus on a particular string inspired version of gaugino mediation in which the first two families are localised at the intersection between D5-branes, whereas the third family and Higgs doublets are allowed to move within the world-volume of one of the branes. The soft supersymmetry breaking third family sfermion mass terms are then in general non-degenerate with the first two families. We place constraints upon parameter space and predictions of flavour changing neutral current effects. Twisted moduli domination is studied and, as well as solving the most serious part of the SUSY flavour problem, is shown to be highly constrained. The constraints are weakened by switching on gravity-mediated contributions from the dilaton and untwisted T-moduli sectors. In the twisted moduli domination limit we predict a stop-heavy MSSM spectrum and quasi-degenerate lightest neutralino and chargino states with wino-dominated mass eigenstates., Comment: 34 pages, 15 figures. Benchmarks in the SUSY Les Houches Accord format can be found http://allanach.home.cern.ch/allanach/benchmarks/int.html, (v2) minor typos corrected, (v3) version accepted by JHEP

We study the Scherk-Schwarz supersymmetry breaking in five-dimensional orbifold theories with five-dimensional fields which are not strictly localized on the boundaries (quasi-localized fields). We show that the Scherk-Schwarz (SS) mechanism, besides the SS parameter \omega, depends upon new parameters, e.g. supersymmetric five-dimensional odd mass terms, governing the level of localization on the boundaries of the five-dimensional fields and study in detail such a dependence. Taking into account radiative corrections, the value of \omega is dynamically allowed to acquire any value in the range 0< \omega < 1/2., Comment: 13 pages, 3 figures

We discuss a new model of quintessence in which the quintessence field is identified with the extra-component of a gauge field in a compactified five-dimensional theory. We show that the extremely tiny energy scale $\sim (3\times 10^{-3} eV)^4$ needed to account for the present acceleration of the Universe can be naturally explained in terms of high energy scales such as the scale of Grand Unification., Comment: 3 pages

Rapid radio intra-day variability (IDV) has been discovered in the southern quasar PKS 1257-326. Flux density changes of up to 40% in as little as 45 minutes have been observed in this source, making it, along with PKS 0405-385 and J1819+3845, one of the three most rapid IDV sources known. We have monitored the IDV in this source with the Australia Telescope Compact Array (ATCA) at 4.8 and 8.6 GHz over the course of the last year, and find a clear annual cycle in the characteristic time-scale of variability. This annual cycle demonstrates unequivocally that interstellar scintillation is the cause of the rapid IDV at radio wavelengths observed in this source. We use the observed annual cycle to constrain the velocity of the scattering material, and the angular size of the scintillating component of PKS 1257-326. We observe a time delay, which also shows an annual cycle, between the similar variability patterns at the two frequencies. We suggest that this is caused by a small (~10 microarcsecond) offset between the centroids of the 4.8 and 8.6 GHz components, and may be due to opacity effects in the source. The statistical properties of the observed scintillation thus enable us to resolve source structure on a scale of ~10 microarcseconds, resolution orders of magnitude higher than current VLBI techniques allow. General implications of scintillation for the physical properties of sources and the turbulent ISM are discussed., Comment: 28 pages, 7 figures. Accepted for publication in the Astrophysical Journal

We discuss how localized twisted moduli in type I string theory can provide a string realization of brane world supersymmetry breaking models., Comment: 5 pages, 2 eps figures, ws-procs9x6.cls included. Based on a talk given by D.R. at 1st International Conference on String Phenomenology, Oxford, England, 6-11 Jul 2002

We analyze the phenomenology of the Higgs sector in a 5D model compactified on an $S_1/Z_2$ orbifold with a compactification scale $M_C \sim {\mathcal O}(TeV)$ where supersymmetry breaking is localized on a brane at one of the fixed points. We show that the conventional MSSM Higgs boson mass bounds in 4D can be violated when we allow the gauge sector, Higgs and third family multiplets to live in the fifth extra dimension., Comment: 5 pages, 3 eps figures, ws-procs9x6.cls included. Based on a talk given by V.D.C. at 1st International Conference on String Phenomenology, Oxford, England, 6-11 Jul 2002

We report the discovery of variable circularly polarised radio emission associated with relativistic ejections from GRS 1915+105, based on observations with the Australia Telescope Compact Array (ATCA) and the Multi-Element Radio-Linked Interferometer Network (MERLIN). Following a radio flare in 2001 January, significant and variable circular polarisation, at a fractional level of 0.2-0.4%, was measured with ATCA at four frequencies between 1-9 GHz. Following an additional outburst 65 days later in 2001 March, further ATCA observations measured a comparable sign and level of circular polarisation at two frequencies. At this second epoch, contemporaneous MERLIN observations directly imaged a relativistic ejection event and allowed us to confidently associate both the circularly and linearly polarised emission with the relativistic ejecta, allowing a detailed measurement of the full polarisation properties in the optically thin phase. The fractional circular polarisation spectrum appears to flatten at higher frequencies in 2001 January, when there is strong evidence for multiple components at different optical depths. While we cannot conclusively distinguish between synchrotron or propagation-induced conversion as the origin of the circularly polarised component, we do not consider that coherent or birefringent scintillation mechanisms are likely. The implication is therefore that the ejections from GRS 1915+105 are associated with a significant population of low-energy electrons, with associated consequences for the energetics of relativistic ejection events. [abridged], Comment: Accepted for publication in MNRAS

We report the cumulative results of five surveys for water maser emission at 1.35 cm wavelength in 131 active galactic nuclei (AGNs) and star-forming galaxies, conducted at the Parkes Observatory between 1993 and 1998. We detected one new maser, in the edge-on galaxy IRASF01063-8034, which exhibits a single, about 0.1 Jy spectral feature at 4282+/-6 km/s (heliocentric) with an unusually large 54+/-16 km/s half-power full width. The centroid velocity of the emission increased to 4319.6+/-0.6 km/s (38+/-2 km/s width) over the 13 days between discovery and confirmation of the detection. A similarly broad linewidth and large change in velocity has been noted for the maser in NGC1052, wherein jet activity excites the emission. Neither optical spectroscopy, radio-infrared correlations, nor infrared colors provide compelling evidence of unusual activity in the nucleus of IRASF01063-8034. Since the galaxy appears to be outwardly normal at optical and infrared wavelengths, detection of a water maser therein is unique. The maser emission is evidence that the galaxy harbors an AGN that is probably obscured by the edge-on galactic disk. The detection highlights the possibility that undetected AGNs could be hidden in other relatively nearby galaxies. No other maser emission features have been identified at velocities between 3084 km/s and 6181 km/s., Comment: To appear in The Astrophysical Journal, 2002 Jan. 20. 29 pages, 6 figures, 3 tables

We consider twisted moduli contributions to supersymmetry breaking in effective type I string constructions involving intersecting D5_i and D9-branes using Goldstino angles to parametrise the supersymmetry breaking. It is well known that twisted moduli enter at tree-level into the gauge kinetic functions, and can provide new sources of gaugino mass if they develop F-term vacuum expectation values. It is generally assumed that string states which are sequestered from the twisted moduli receive a zero soft mass in the twisted modulus domination limit, however the standard form of Kahler potential does not reproduce this expectation. We therefore propose a new form of the Kahler potential which is consistent at leading order with the sequestered form proposed by Randall and Sundrum, and show that it leads to exponentially suppressed sequestered soft masses. Including the effects of Green-Schwarz mixing, we write down the soft scalar masses and trilinears arising from a type I string construction involving intersecting D5_i and D9-branes in the presence of untwisted and twisted moduli. If the squarks and sleptons are identified with sequestered states then in the twisted moduli dominated limit this corresponds to gaugino mediated supersymmetry breaking, and we discuss two different scenarios for this. The general results will be useful for phenomenological studies involving a combination of gravity and gaugino mediated SUSY breaking due to the dilaton, untwisted and twisted moduli contributions, and enable the soft masses to be studied as a function of the different compactification radii., Comment: Additional appendix generalises results for alternative exponential suppression factor. Version accepted for publicaton in JHEP

We consider the Standard Models of particle physics and hot big bang cosmology, and review the theoretical and experimental motivations for extending these models to include supersymmetry and inflation. An obvious extension would be to unite these two models into a single all-encompassing theory. We identify a list of theoretical challenges that such a theory must address, which we illustrate with a simple model - a variant of the next-to-minimal supersymmetric Standard Model - that addresses these challenges., Comment: This is a review article to be published in J.Phys.G. Based on a plenary talk given by S.F.K. at the IPPP BSM Workshop, Durham, UK 6-11th May 2001. 16 pages, Latex

We report high sensitivity dual-frequency observations of radio oscillations from GRS 1915+105 following the decay of a major flare event in 2000 July. The oscillations are clearly observed at both frequencies, and the time-resolved spectral index traces the events between optically thin and thick states. While previously anticipated from sparse observations and simple theory, this is the first time a quasi-periodic signal has been seen in the radio spectrum, and is a clear demonstration that flat radio spectra can arise from the combination of emission from optically thick and thin regions. In addition, we measure the linear polarisation of the oscillations, at both frequencies, at a level of about 1--2%, with a flat spectrum. Cross-correlating the two light curves we find a mean delay, in the sense that the emission at 8640 MHz leads that at 4800 MHz, of around 600 seconds. Comparison with frequency-dependent time delays reported in the literature reveals that this delay is variable between epochs. We briefly discuss possible origins for a varying time delay, and suggest possible consequences., Comment: Accepted for publication in MNRAS

We consider the problem of supersymmetry and electroweak breaking in a 5d theory compactified on an $S^{1}/Z_{2}$ orbifold, where the extra dimension may be large or small. We consider the case of a supersymmetry breaking 4d brane located at one of the orbifold fixed points with the Standard Model gauge sector, third family and Higgs fields in the 5d bulk, and the first two families on a parallel 4d matter brane located at the other fixed point. We compute the Kaluza-Klein mass spectrum in this theory using a matrix technique which allows us to interpolate between large and small extra dimensions. We also consider the problem of electroweak symmetry breaking in this theory and localize the Yukawa couplings on the 4d matter brane spatially separated from the brane where supersymmetry is broken. We calculate the 1-loop effective potential using a zeta-function regularization technique, and find that the dominant top and stop contributions are separately finite. Using this result we find consistent electroweak symmetry breaking for a compactification scale {$ 1/R \approx 830$ GeV} and a lightest Higgs boson mass $m_{h} \approx 170$ GeV., Comment: Typos corrected, version accepted for publication in Nucl.Phys.B

We propose a mechanism for mediating supersymmetry breaking in Type I string constructions. The basic set-up consists of a system of three D-branes: two parallel D-branes, a matter D-brane and a source D-brane, with supersymmetry breaking communicated via a third D-brane, the mediating D-brane, which intersects both of the parallel D-branes. We discuss an example in which the first and second family matter fields correspond to open strings living on the intersection of the matter D-brane and mediating D-brane, while the gauge fields, Higgs doublets and third family matter fields correspond to open strings living on the mediating D-brane. As in gaugino mediated models, the gauginos and Higgs doublets receive direct soft masses from the source brane, and flavour-changing neutral currents are naturally suppressed since the first and second family squarks and sleptons receive suppressed soft masses. However, unlike the gaugino mediated model, the third family squarks and sleptons receive unsuppressed soft masses, resulting in a very distinctive spectrum with heavier stops, sbottoms and staus., Comment: Version to appear in Nucl.Phys.B. 28 pages, Latex

We report strong variability in the circular and linear polarization of the intraday variable source PKS 1519-273. The circular polarization varies on a timescale of hours to days at frequencies between 1.4 and 8.6 GHz, and is strongly correlated with variations in the total intensity at 4.8 and 8.6 GHz. We argue that the variability is due to interstellar scintillation of a highly compact (15-35 \mu as) component of the source with -3.8\pm 0.4% circular polarization at 4.8 GHz. We find that no simple model for the circular polarization can account for both the high magnitude and the frequency dependence in PKS 1519-273 at centimeter wavelengths., Comment: 5 pages, 3 figures, ApJ accepted

We have used the Australia Telescope Compact Array (ATCA) to search for 6.7-GHz methanol maser emission towards 87 galaxies. We chose the target sources using several criteria, including far-IR luminosities and the presence of known OH megamasers. In addition, we searched for methanol masers in the nearby starburst galaxy NGC 253, making a full spectral-line synthesis image. No emission was detected in any galaxies, with detection limits ranging from 25 mJy to 75 mJy. This is surprising, given the close association of OH and methanol masers in Galactic star-formation regions, and significantly constrains models of OH megamaser emission. This absence of maser emission may be a result of low methanol abundances in molecular clouds in starburst galaxies., Comment: 7 Pages, no figures, Accepted for publication in MNRAS