32 research outputs found
Gaugino Condensation and Nonperturbative Superpotentials in Flux Compactifications
There are two known sources of nonperturbative superpotentials for K\"ahler
moduli in type IIB orientifolds, or F-theory compactifications on Calabi-Yau
fourfolds, with flux: Euclidean brane instantons and low-energy dynamics in D7
brane gauge theories. The first class of effects, Euclidean D3 branes which
lift in M-theory to M5 branes wrapping divisors of arithmetic genus 1 in the
fourfold, is relatively well understood. The second class has been less
explored. In this paper, we consider the explicit example of F-theory on with flux. The fluxes lift the D7 brane matter fields, and stabilize
stacks of D7 branes at loci of enhanced gauge symmetry. The resulting theories
exhibit gaugino condensation, and generate a nonperturbative superpotential for
K\"ahler moduli. We describe how the relevant geometries in general contain
cycles of arithmetic genus (and how divisors can
contribute to the superpotential, in the presence of flux). This second class
of effects is likely to be important in finding even larger classes of models
where the KKLT mechanism of moduli stabilization can be realized. We also
address various claims about the situation for IIB models with a single
K\"ahler modulus.Comment: 24 pages, harvmac, no figures, references adde
Subsurface signatures and timing of extreme wave events along the Southeast Indian coast
Written history's limitation becomes apparent when attempting to document the predecessors of extreme coastal events in the Indian Ocean, from 550-700 years in Thailand and 1000 years in Indonesia. Detailed ground-penetrating radar (GPR) surveys in Mahabalipuram, southeast India, complemented with sedimentological analyses, magnetic susceptibility measurements, and optical dating provide strong evidence of extreme wave events during the past 3700 years. The diagnostic event signatures include the extent and elevation of the deposits, as well as morphologic similarity of buried erosional scarps to those reported in northern Sumatra region. Optical ages immediately overlying the imaged discontinuities that coincides with high concentration of heavy minerals date the erosional events to 340 ± 35, 350 ± 20, 490 ± 30, 880 ± 40, 1080 ± 60, 1175 ± 188, 2193 ± 266, 2235 ± 881, 2489 ± 293, 2450 ± 130, 2585 ± 609, 3710 ± 200 years ago. These evidences are crucial in reconstructing paleo extreme wave events and will pave the way for regional correlation of erosional horizons along the northern margin of Indian Ocean
Flux Compactifications on Calabi-Yau Threefolds
The presence of RR and NS three-form fluxes in type IIB string
compactification on a Calabi-Yau orientifold gives rise to a nontrivial
superpotential W for the dilaton and complex structure moduli. This
superpotential is computable in terms of the period integrals of the Calabi-Yau
manifold. In this paper, we present explicit examples of both supersymmetric
and nonsupersymmetric solutions to the resulting 4d N=1 supersymmetric no-scale
supergravity, including some nonsupersymmetric solutions with relatively small
values of W. Our examples arise on orientifolds of the hypersurfaces in
and . They serve as explicit
illustrations of several of the ingredients which have played a role in the
recent proposals for constructing de Sitter vacua of string theory.Comment: 30 pages, harvmac big; refs and minor comments adde
Moduli Stabilization from Fluxes in a Simple IIB Orientifold
We study novel type IIB compactifications on the T^6/Z_2 orientifold. This
geometry arises in the T-dual description of Type I theory on T^6, and one
normally introduces 16 space-filling D3-branes to cancel the RR tadpoles. Here,
we cancel the RR tadpoles either partially or fully by turning on three-form
flux in the compact geometry. The resulting (super)potential for moduli is
calculable. We demonstrate that one can find many examples of N=1
supersymmetric vacua with greatly reduced numbers of moduli in this system. A
few examples with N>1 supersymmetry or complete supersymmetry breaking are also
discussed.Comment: 49 pages, harvmac big; v2, corrected some typo
Towards Inflation in String Theory
We investigate the embedding of brane inflation into stable compactifications
of string theory. At first sight a warped compactification geometry seems to
produce a naturally flat inflaton potential, evading one well-known difficulty
of brane-antibrane scenarios. Careful consideration of the closed string moduli
reveals a further obstacle: superpotential stabilization of the
compactification volume typically modifies the inflaton potential and renders
it too steep for inflation. We discuss the non-generic conditions under which
this problem does not arise. We conclude that brane inflation models can only
work if restrictive assumptions about the method of volume stabilization, the
warping of the internal space, and the source of inflationary energy are
satisfied. We argue that this may not be a real problem, given the large range
of available fluxes and background geometries in string theory.Comment: 41 pages, harvmac; v2: results of appendix A extended to include
branes at angles, typos corrected, refs adde
What does inflation really predict?
If the inflaton potential has multiple minima, as may be expected in, e.g.,
the string theory "landscape", inflation predicts a probability distribution
for the cosmological parameters describing spatial curvature (Omega_tot), dark
energy (rho_Lambda, w, etc.), the primordial density fluctuations (Omega_tot,
dark energy (rho_Lambda, w, etc.). We compute this multivariate probability
distribution for various classes of single-field slow-roll models, exploring
its dependence on the characteristic inflationary energy scales, the shape of
the potential V and and the choice of measure underlying the calculation. We
find that unless the characteristic scale Delta-phi on which V varies happens
to be near the Planck scale, the only aspect of V that matters observationally
is the statistical distribution of its peaks and troughs. For all energy scales
and plausible measures considered, we obtain the predictions Omega_tot ~
1+-0.00001, w=-1 and rho_Lambda in the observed ballpark but uncomfortably
high. The high energy limit predicts n_s ~ 0.96, dn_s/dlnk ~ -0.0006, r ~ 0.15
and n_t ~ -0.02, consistent with observational data and indistinguishable from
eternal phi^2-inflation. The low-energy limit predicts 5 parameters but prefers
larger Q and redder n_s than observed. We discuss the coolness problem, the
smoothness problem and the pothole paradox, which severely limit the viable
class of models and measures. Our findings bode well for detecting an
inflationary gravitational wave signature with future CMB polarization
experiments, with the arguably best-motivated single-field models favoring the
detectable level r ~ 0.03. (Abridged)Comment: Replaced to match accepted JCAP version. Improved discussion,
references. 42 pages, 17 fig
Minimal information for studies of extracellular vesicles (MISEV2023): From basic to advanced approaches
Extracellular vesicles (EVs), through their complex cargo, can reflect the state of their cell of origin and change the functions and phenotypes of other cells. These features indicate strong biomarker and therapeutic potential and have generated broad interest, as evidenced by the steady year-on-year increase in the numbers of scientific publications about EVs. Important advances have been made in EV metrology and in understanding and applying EV biology. However, hurdles remain to realising the potential of EVs in domains ranging from basic biology to clinical applications due to challenges in EV nomenclature, separation from non-vesicular extracellular particles, characterisation and functional studies. To address the challenges and opportunities in this rapidly evolving field, the International Society for Extracellular Vesicles (ISEV) updates its 'Minimal Information for Studies of Extracellular Vesicles', which was first published in 2014 and then in 2018 as MISEV2014 and MISEV2018, respectively. The goal of the current document, MISEV2023, is to provide researchers with an updated snapshot of available approaches and their advantages and limitations for production, separation and characterisation of EVs from multiple sources, including cell culture, body fluids and solid tissues. In addition to presenting the latest state of the art in basic principles of EV research, this document also covers advanced techniques and approaches that are currently expanding the boundaries of the field. MISEV2023 also includes new sections on EV release and uptake and a brief discussion of in vivo approaches to study EVs. Compiling feedback from ISEV expert task forces and more than 1000 researchers, this document conveys the current state of EV research to facilitate robust scientific discoveries and move the field forward even more rapidly
High specific-energy lead-acid batteries through organic metals
A novel room-temperature route to corrosion protect lead-coated plastic grids with an organic metal, namely, polyaniline, for producing commercial-grade high specific-energy 12 V/45 Ah lead-acid batteries is reported. The specific energy of these lead-acid batteries is found to be ca. 45 Wh/kg as against about 30 Wh/kg for conventional lead-acid batteries. It is believed that the study reported here will open up a new realm of possibilities for lead-acid battery development, and will contribute directly towards lowering the cost of both battery materials and manufacturing