A
bstract
A longstanding question in superstring/
M
theory is does it predict supersymmetry below the string scale? We formulate and discuss a necessary condition for this to be true; this is the ...mathematical conjecture that all stable, compact Ricci flat manifolds have special holonomy in dimensions below eleven. Almost equivalent is the proposal that the landscape of all geometric, stable, string/
M
theory compactifications to Minkowski spacetime (at leading order) are supersymmetric. For simply connected manifolds, we collect together a number of physically relevant mathematical results, emphasising some key outstanding problems and perhaps less well known results. For non-simply connected, non-supersymmetric Ricci flat manifolds we demonstrate that many cases suffer from generalised Witten bubble of nothing instabilities.
We study the prospects of searches for exotic long-lived particles with the MoEDAL detector at the LHC, assuming the integrated luminosity of 30 fb
-
1
that is expected at the end of Run 3. MoEDAL ...incorporates nuclear track detectors deployed a few metres away from the interaction point, which are sensitive to any highly-ionizing particles. Hence MoEDAL is able to detect singly- or doubly-charged particles with low velocities
β
<
0.15
or
<
0.3
, respectively, and lifetimes larger than
O
(
1
)
m
/
c
. We examine the MoEDAL sensitivity to various singly-charged supersymmetric particles with long lifetimes and to several types of doubly-charged long-lived particles with different spins and SU(2) charges. We compare the prospective MoEDAL mass reaches to current limits from ATLAS and CMS, which involve auxiliary analysis assumptions. MoEDAL searches for doubly-charged fermions are particularly competitive.
A
bstract
Ricci flat manifolds of special holonomy are a rich framework as models of the extra dimensions in string/
M
-theory. At special points in vacuum moduli space, special kinds of ...singularities occur and demand a physical interpretation. In this paper we show that the topologically distinct
G
2
-holonomy manifolds arising from desingularisations of codimension four orbifold singularities due to Joyce and Karigiannis correspond physically to Coulomb and Higgs phases of four dimensional gauge theories. The results suggest generalisations of the Joyce-Karigiannis construction to arbitrary ADE-singularities and higher order twists which we explore in detail in explicitly solvable local models. These models allow us to derive an isomorphism between moduli spaces of Ricci flat metrics on these non-compact
G
2
-manifolds and flat ADE-connections on compact flat 3-manifolds which we establish explicitly for SU(
n
).
Abstract Ricci flat manifolds of special holonomy are a rich framework as models of the extra dimensions in string/M-theory. At special points in vacuum moduli space, special kinds of singularities ...occur and demand a physical interpretation. In this paper we show that the topologically distinct G 2-holonomy manifolds arising from desingularisations of codimension four orbifold singularities due to Joyce and Karigiannis correspond physically to Coulomb and Higgs phases of four dimensional gauge theories. The results suggest generalisations of the Joyce-Karigiannis construction to arbitrary ADE-singularities and higher order twists which we explore in detail in explicitly solvable local models. These models allow us to derive an isomorphism between moduli spaces of Ricci flat metrics on these non-compact G 2-manifolds and flat ADE-connections on compact flat 3-manifolds which we establish explicitly for SU(n).
Copper doped NiO thin films have been prepared using chemical spray pyrolysis technique. Investigation of these films has been done using X-ray diffraction, Atomic force microscopy, two-probe ...resistivity measurements and UV–visible spectroscopy. Interesting results have been obtained from the study of optical spectra. A peak corresponding to 439 nm has been observed in the absorption spectra for 1%, 5% and 10% copper doped samples. The area of the peak increases with the increase in copper concentration. This result is consistent with the AFM data. The resistivity results show that the activation energy decreases with the increase in the copper concentration. The low temperature conduction has been explained by variable range-hopping mechanism, which fits very well for the whole temperature range and again is consistent with the absorbance data. Value addition to this study is the observation of higher absorption in the visible region, thereby a tendency towards tunability for applications.
Zinc oxide doped with Al (AZO) thin films were prepared on borosilicate glass substrates by dip and dry technique using sodium zincate bath. Effects of doping on the structural and optical properties ...of ZnO film were investigated by XRD, EPMA, AFM, optical transmittance, PL and Raman spectroscopy. The band gap for ZnO:Al (5.0
at.
wt.%) film was found to be 3.29
eV compared with 3.25
eV band gap for pure ZnO film. Doping with Al introduces aggregation of crystallites to form micro-size clusters affecting the smoothness of the film surface. Al
3+ ion was found to promote chemisorption of oxygen into the film, which in turn affects the roughness of the sample. Six photoluminescence bands were observed at 390, 419, 449, 480, 525 and 574
nm in the emission spectra. Excitation spectra of ZnO film showed bands at 200, 217, 232 and 328
nm, whereas bands at 200, 235, 257 and 267
nm were observed for ZnO:Al film. On the basis of transitions from conduction band or deep donors (CB, Zn
i
or
V
OZn
i
) to valence band and/or deep acceptor states (VB,
V
Zn or O
i
or O
Zn), a tentative model has been proposed to explain the PL spectra. Doping with Al
3+ ions reduced the polar character of the film. This has been confirmed from laser Raman studies.
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•Ultrasound assisted synthesis of ZnO:Au nanorods.•Lattice expansion in ZnO with Au incorporation.•ZnO:Au shows high UV absorbance to be used as UV blocking agents.•Enhanced PL ...emission in green region may find application in LEDs.
Au doped ZnO (ZnO:Au) nanostructures were synthesized by ultrasound assisted wet chemical method. The concentration of dopant was varied and both structural and optical properties of ZnO:Au were investigated. The crystal structure and morphology of the samples were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). These results showed the formation of nanorods of ZnO:Au having wurtzite structure and c-axis orientation. Gradual increase in crystallite size and bond length was also observed with the increase in gold concentration in ZnO intending the expansion of lattice after gold doping. The optical absorption measurements showed high ultraviolet (UV) absorbance property of ZnO:Au with sharp and intense absorption band in this region as compared to pristine ZnO. Photoluminescence (PL) measurements showed excitonic emission band of ZnO around 390nm for both undoped and Au doped ZnO nanoparticles. Further, a strong emission around 467nm was observed in the PL spectra of ZnO/ZnO:Au which was attributed to the transitions related to excess of oxygen vacancies. Interestingly, a new band was observed at 582nm for doped ZnO samples which grew in intensity with doping concentration. This band was ascribed to the gold nanoparticle adsorbed on the surface of ZnO.
Aims. The nearby TeV blazar 1ES 1959+650 (z = 0.047) was reported to be in flaring state during June–July 2016 by Fermi-LAT, FACT, MAGIC and VERITAS collaborations. We studied the spectral energy ...distributions (SEDs) in different states of the flare during MJD 57530–57589 using simultaneous multiwaveband data with the aim of understanding the possible broadband emission scenario during the flare. Methods. The UV-optical and X-ray data from UVOT and XRT respectively on board Swift and high energy γ-ray data from Fermi-LAT were used to generate multiwaveband lightcurves as well as to obtain high flux states and quiescent state SEDs. The correlation and lag between different energy bands was quantified using discrete correlation function. The synchrotron self-Compton (SSC) model was used to reproduce the observed SEDs during flaring and quiescent states of the source. Results. A good correlation is seen between X-ray and high energy γ-ray fluxes. The spectral hardening with increase in the flux is seen in X-ray band. The power law index vs. flux plot in γ-ray band indicates the different emission regions for 0.1–3 GeV and 3–300 GeV energy photons. Two zone SSC model satisfactorily fits the observed broadband SEDs. The inner zone is mainly responsible for producing synchrotron peak and high energy γ-ray part of the SED in all states. The second zone is mainly required to produce less variable optical-UV and low energy γ-ray emission. Conclusions. Conventional single zone SSC model does not satisfactorily explain broadband emission during observation period considered. There is an indication of two emission zones in the jet which are responsible for producing broadband emission from optical to high energy γ-rays.
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► Photocatalytic degradation and toxicity reduction of NR dye was carried out. ► Degradation was performed using synthesized BiOCl. ► Formation of OH verified by fluorescence ...technology. ► Photodegradation of textile dye reduced the acute toxicity to marine bacteria Vibrio fischeri. ► Mineralization of NR confirmed by COD and nitrate anions production.
The BiOCl catalyst was prepared by hydrolysis method. The compound was extensively characterized by XRD, SEM, TEM, UV–vis measurements and BET surface area. The prepared material had average pore diameter about 6–13nm. The BET surface area of the sample is about 40m2/g. The photocatalytic degradation and toxicity reduction of textile dye neutral red (NR) was investigated in the presence of as prepared BiOCl. The analysis of OH radical formation was performed by fluorescence technique. The intermediates and the final products of degradation were detected by high-performance liquid chromatography–photodiode array-electrospray ionization-mass spectrometry (HPLC–ESI-DAD-MS) technology. Decrease in chemical oxygen demand (COD) and dye absorbance of the photodegraded dye solution revealed a complete mineralization of NR into CO2 and inorganic ions. The recycling experiments confirmed the relative stability of the catalyst. Finally, the luminescent marine bacteria Vibrio fischeri was used to assess the acute toxicity of samples prior to and after the photocatalytic treatment and it was found that toxicity was fully eliminated following photocatalytic degradation.
Abstract A recent theorem of Foscolo-Haskins-Nordström 1 which constructs complete G 2-holonomy orbifolds from circle bundles over Calabi-Yau cones can be utilised to construct and investigate a ...large class of generalisations of the M-theory flop transition. We see that in many cases a UV perturbative gauge theory appears to have an infrared dual described by a smooth G 2-holonomy background in M-theory. Various physical checks of this proposal are carried out affirmatively.
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