977 research outputs found

    Fatal attraction: more on decaying anti-branes

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    We elaborate on the decay of branes inside throat geometries that are supported by flux carrying charges opposite to the brane. Our main point is that such backgrounds necessarily have a local, possibly diverging, pile up of brane-charges dissolved in flux around the anti-brane due to the (fatal) attraction of the flux towards the brane. We explain that this causes enhanced brane-flux annihilation and is in tension with the idea that anti-branes can be used to construct meta-stable vacua. We argue that stable configurations -- if they at all exist -- are not obtainable within SUGR. The problem we point out is already present when the back-reaction is confined in the IR and the associated uplift energy small. Our results are valid in the regime that is complementary to a recent analysis of Bena et. al.Comment: 24 pages, 5 figures, v2.: few typos correcte

    A note on obstinate tachyons in classical dS solutions

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    The stabilisation of the dilaton and volume in tree-level flux compactifications leads to model independent and thus very powerful existence and stability criteria for dS solutions. In this paper we show that the sizes of cycles wrapped by orientifold planes are scalars whose scalings in the potential are not entirely model independent, but enough to entail strong stability constraints. For all known dS solutions arising from massive IIA supergravity flux compactifications on SU(3)-structure manifolds the tachyons are exactly within the subspace spanned by the dilaton, the total volume and the volumes of the orientifold cycles. We illustrate this in detail for the well-studied case of the O6 plane compactification on SU(2)xSU(2)/Z_2xZ_2. For that example we uncover another novel structure in the tachyon spectrum: the dS solutions have a singular, but supersymmetric, Minkowski limit, in which the tachyon exactly aligns with the sgoldstino.Comment: 22 pages; v2: added references, minor change

    A note on smeared branes in flux vacua and gauged supergravity

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    In the known examples of flux vacua with calibrated spacetime-filling sources (branes or orientifold planes), one can smear the source in order to perform a standard KK reduction and obtain a lower-dimensional supergravity description. Furthermore, it is expected that the smeared and localized solution preserve equal amounts of supersymmetry. In this note we point out that the AdS7\mathrm{AdS}_7 solution discussed in arXiv:1111.2605 and arXiv:1309.2949 is a counterexample to this common lore. The solution is supersymmetric when the spacetime-filling D6-branes are localized but breaks supersymmetry in the smeared limit. By using the embedding tensor formalism we demonstrate that there is no gauged supergravity description for the solution, regardless of the source being smeared or not. We conjecture that for flux solutions with separation between the KK scale and the AdS radius this cannot occur.Comment: 23 pages, LaTeX, no figures; added reference for section

    Non-relativistic strings and branes as non-linear realizations of Galilei groups

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    We construct actions for non-relativistic strings and membranes purely as Wess-Zumino terms of the underlying Galilei groups.Comment: references adde

    (Anti-)Brane backreaction beyond perturbation theory

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    We improve on the understanding of the backreaction of anti-D6-branes in a flux background that is mutually BPS with D6-branes. This setup is analogous to the study of the backreaction of anti-D3-branes inserted in the KS throat, but does not require us to smear the anti-branes or do a perturbative analysis around the BPS background. We solve the full equations of motion near the anti-D6-branes and show that only two boundary conditions are consistent with the equations of motion. Upon invoking a topological argument we eliminate the boundary condition with regular H flux since it cannot lead to a solution that approaches the right kind of flux away from the anti-D6-brane. This leaves us with a boundary condition which has singular, but integrable, H flux energy density.Comment: 12 pages + appendices, 1 figure; v2: minor changes, version published in JHE

    More than just contraception : the impact of the levonorgestrel-releasing intrauterine system on public health over 30 years

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    Universal access to sexual and reproductive health services is essential to facilitate the empowerment of women and achievement of gender equality. Increasing access to modern methods of contraception can reduce the incidence of unplanned pregnancy and decrease maternal mortality. Long-acting reversible contraceptives (LARCs) offer high contraceptive efficacy as well as cost-efficacy, providing benefits for both women and healthcare systems. The levonorgestrel-releasing intrauterine system (LNG-IUS) first became available in 1990 with the introduction of Mirena (LNG-IUS 20), a highly effective contraceptive which can reduce menstrual blood loss and provide other therapeutic benefits. The impact of the LNG-IUS on society has been wide ranging, including decreasing the need for abortion, reducing the number of surgical sterilisation procedures performed, as well as reducing the number of hysterectomies carried out for issues such as heavy menstrual bleeding (HMB). In the context of the COVID-19 pandemic, Mirena can provide a treatment option for women with gynaecological issues such as HMB without organic pathology, minimising exposure to the hospital environment and reducing waiting times for surgical appointments. Looking to the future, research and development in the field of the LNG-IUS continues to expand our understanding of these contraceptives in clinical practice and offers the potential to further expand the choices available to women, allowing them to select the option that best meets their needs.Non peer reviewe

    Thirty years of mirena : A story of innovation and change in women's healthcare

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    Since its introduction in 1990, the levonorgestrel-releasing intrauterine system (LNG-IUS) has played a key role in shaping the healthcare landscape of women. Here we explore the development of the first LNG-IUS (Mirena (R)) and the early clinical trials that demonstrated its potential. We highlight the contraceptive and therapeutic benefits of Mirena (R), and discuss how clinical practice has been changed since the introduction of LNG-IUS and other long-acting reversible contraceptive methods. The history of Mirena (R) is rich in innovation and has also paved the way to the development of smaller intrauterine systems with lower hormone doses. Along with Mirena (R), these newer LNG-IUS contribute to improving contraceptive choices for women, allowing them to select the option that is right for them and that meets their needs no matter their age, parity or circumstances.Non peer reviewe