518 research outputs found
Flux moduli stabilisation, Supergravity algebras and no-go theorems
We perform a complete classification of the flux-induced 12d algebras
compatible with the set of N=1 type II orientifold models that are T-duality
invariant, and allowed by the symmetries of the T^6/(Z_2 x Z_2) isotropic
orbifold. The classification is performed in a type IIB frame, where only H_3
and Q fluxes are present. We then study no-go theorems, formulated in a type
IIA frame, on the existence of Minkowski/de Sitter (Mkw/dS) vacua. By deriving
a dictionary between the sources of potential energy for the three moduli (S, T
and U) in types IIA and IIB, we are able to combine algebra results and no-go
theorems. The outcome is a systematic procedure for identifying
phenomenologically viable models where Mkw/dS vacua may exist. We present a
complete table of the allowed algebras and the viability of their resulting
scalar potential, and we point at the models which stand any chance of
producing a fully stable vacuum.Comment: Version published in JHE
Exceptional Flux Compactifications
We consider type II (non-)geometric flux backgrounds in the absence of brane
sources, and construct their explicit embedding into maximal gauged D=4
supergravity. This enables one to investigate the critical points, mass spectra
and gauge groups of such backgrounds. We focus on a class of type IIA geometric
vacua and find a novel, non-supersymmetric and stable AdS vacuum in maximal
supergravity with a non-semisimple gauge group. Our construction relies on a
non-trivial mapping between SL(2) x SO(6,6) fluxes, SU(8) mass spectra and
gaugings of E7(7) subgroups.Comment: 51 pages, 2 figures and 4 tables. v3: change of SO(6,6) spinorial
conventions, published versio
Populating the swampland: the case of U(1)^496 and E_8 x U(1)^248
For d=10 N=1 SUGRA coupled to d=10 N=1 SYM, anomaly cancellation places
severe constraints on the allowed gauge groups. Besides the ones known to
appear in string theory, only U(1)^496 and E_8 x U(1)^248 are allowed. There
are no known theories of quantum gravity that reduce in some limit to these two
last supergravity theories, and in this note I present some evidence that those
quantum theories might not exist. The first observation is that, upon
compactification, requring that the quantum theory possesses a moduli space
with finite volume typically implies the existence of singularities where the
4d gauge group is enhanced, but for these two theories that gauge enhancement
is problematic from the 10d point of view. I also point out that while these
four supergravity theories present repulson-type singularities, the known
mechanism that repairs those singularities for the first two - the non-Abelian
enhancon - is not available for the last two theories. In short, these two
supergravity theories might be too Abelian for their own good.Comment: 12 page
Physiotherapy, and speech and language therapy intervention for patients with refractory chronic cough: a multicentre randomised control trial.
BACKGROUND: Physiotherapy, and speech and language therapy are emerging non-pharmacological treatments for refractory chronic cough. We aimed to investigate the efficacy of a physiotherapy, and speech and language therapy intervention (PSALTI) to improve health-related quality of life (HRQoL) and to reduce cough frequency in patients with refractory chronic cough. METHODS: In this multicentre randomised controlled trial, patients with refractory chronic cough were randomised to four weekly 1:1 sessions of either PSALTI consisting of education, laryngeal hygiene and hydration, cough suppression techniques, breathing exercises and psychoeducational counselling or control intervention consisting of healthy lifestyle advice. We assessed the change in HRQoL at week 4 with the Leicester Cough Questionnaire (LCQ). Secondary efficacy outcomes included 24-hour objective cough frequency (Leicester Cough Monitor) and cough reflex sensitivity. The primary analysis used an analysis of covariance adjusted for baseline measurements with the intention-to-treat population. This study was registered at UK Clinical Research Network (UKCRN ID 10678). FINDINGS: Between December 2011 and April 2014, we randomly assigned 75 participants who underwent baseline assessment (34 PSALTI and 41 controls). In the observed case analysis, HRQoL (LCQ) improved on average by 1.53 (95% CI 0.21 to 2.85) points more in PSALTI group than with control (p=0.024). Cough frequency decreased by 41% (95% CI 36% to 95%) in PSALTI group relative to control (p=0.030). The improvements within the PSALTI group were sustained up to 3 months. There was no significant difference between groups in the concentration of capsaicin causing five or more coughs. INTERPRETATION: Greater improvements in HRQoL and cough frequency were observed with PSALTI intervention. Our findings support the use of PSALTI for patients with refractory chronic cough. TRIAL REGISTRATION NUMBER: UKCRN ID 10678 and ISRCTN 73039760; Results
Critical Trapped Surfaces Formation in the Collision of Ultrarelativistic Charges in (A)dS
We study the formation of marginally trapped surfaces in the head-on
collision of two ultrarelativistic charges in space-time. The metric of
ultrarelativistic charged particles in is obtained by boosting
Reissner-Nordstr\"om space-time to the speed of light. We show that
formation of trapped surfaces on the past light cone is only possible when
charge is below certain critical - situation similar to the collision of two
ultrarelativistic charges in Minkowski space-time. This critical value depends
on the energy of colliding particles and the value of a cosmological constant.
There is richer structure of critical domains in case. In this case
already for chargeless particles there is a critical value of the cosmological
constant only below which trapped surfaces formation is possible. Appearance of
arbitrary small nonzero charge significantly changes the physical picture.
Critical effect which has been observed in the neutral case does not take place
more. If the value of the charge is not very large solution to the equation on
trapped surface exists for any values of cosmological radius and energy density
of shock waves. Increasing of the charge leads to decrease of the trapped
surface area, and at some critical point the formation of trapped surfaces of
the type mentioned above becomes impossible.Comment: 30 pages, Latex, 7 figures, Refs. added and typos correcte
Moduli Stabilization and Cosmology of Type IIB on SU(2)-Structure Orientifolds
We consider type IIB flux compactifications on six-dimensional
SU(2)-structure manifolds with O5- and O7-planes. These six-dimensional spaces
allow not only for F_3 and H_3 fluxes but also for F_1 and F_5 fluxes. We
derive the four-dimensional N=1 scalar potential for such compactifications and
present one explicit example of a fully stabilized AdS vacuum with large volume
and small string coupling. We then discuss cosmological aspects of these
compactifications and derive several no-go theorems that forbid dS vacua and
slow-roll inflation under certain conditions. We also study concrete examples
of cosets and twisted tori and find that our no-go theorems forbid dS vacua and
slow-roll inflation in all but one of them. For the latter we find a dS
critical point with \epsilon numerically zero. However, the point has two
tachyons and eta-parameter \eta \approx -3.1.Comment: 35 pages + appendices, LaTeX2e; v2: numerical dS extremum added,
typos corrected, references adde
Charting the landscape of N=4 flux compactifications
We analyse the vacuum structure of isotropic Z_2 x Z_2 flux
compactifications, allowing for a single set of sources. Combining algebraic
geometry with supergravity techniques, we are able to classify all vacua for
both type IIA and IIB backgrounds with arbitrary gauge and geometric fluxes.
Surprisingly, geometric IIA compactifications lead to a unique theory with four
different vacua. In this case we also perform the general analysis allowing for
sources compatible with minimal supersymmetry. Moreover, some relevant examples
of type IIB non-geometric compactifications are studied. The computation of the
full N=4 mass spectrum reveals the presence of a number of non-supersymmetric
and nevertheless stable AdS_4 vacua. In addition we find a novel dS_4 solution
based on a non-semisimple gauging.Comment: Minor corrections and references added. Version published in JHE
No Forbidden Landscape in String/M-theory
Scale invariant but non-conformal field theories are forbidden in (1+1)
dimension, and so should be the corresponding holographic dual gravity
theories. We conjecture that such scale invariant but non-conformal field
configurations do not exist in the string/M-theory. We provide a proof of this
conjecture in the classical supergravity limit under a certain gauge condition.
Our proof does also apply in higher dimensional scale invariant but
non-conformal field configurations, which suggests that scale invariant but
non-conformal field theories may be forbidden in higher dimensions as well.Comment: 14 pages, v2: energy condition on c-theorem is corrected, v3: extra
assumption in the proof is discussed due to a sign error in the previous
versio
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