1,721,028 research outputs found
Elliptic threefolds with high Mordell-Weil rank
Full text linkWe present the first examples of smooth elliptic Calabi-Yau threefolds with
Mordell-Weil rank 10, the highest currently known value. They are given by the
Schoen threefolds introduced by Namikawa; there are six isolated fibers of
Kodaira Type IV. We explicitly compute the Shioda homomorphism for the
generators of the Mordell-Weil group and their induced height pairing.
Compactification of F-theory on these threefolds gives an effective theory in
six dimensions which contains ten abelian gauge group factors. We compute the
massless matter spectrum. In particular, we show that the charged singlet
matter need not reside at enhancement loci of Type , as previously
believed. We relate the multiplicities of the massless spectrum to genus-zero
Gopakumar-Vafa invariants and other geometric quantities of the Calabi-Yau. We
show that the gravitational and abelian anomaly cancellation conditions are
satisfied. We prove a Geometric Anomaly Cancellation equation and we deduce
birational equivalence for the quantities in the spectrum. We explicitly
describe a Weierstrass model over of the Calabi-Yau threefolds as
a log canonical model and compare it to a construction by Elkies and classical
results of Burkhardt.Comment: Final versio
Terminal singularities, Milnor numbers, and matter in F-theory
Full text linkWe initiate a systematic investigation of F-theory on elliptic fibrations with singularities which cannot be resolved without breaking the Calabi–Yau condition, corresponding to Q-factorial terminal singularities. It is the purpose of this paper to elucidate the physical origin of such non-crepant singularities in codimension two and to systematically analyze F-theory compactifications containing such singularities. The singularities reflect the presence of localized matter states from wrapped M2-branes which are not charged under any massless gauge potential. We identify a class of Q-factorial terminal singularities on elliptically fibered Calabi–Yau threefolds for which we can compute the number of uncharged localized hypermultiplets in terms of their associated Milnor numbers. These count the local complex deformations of the singularities. The resulting six-dimensional spectra are shown to be anomaly-free. We exemplify this in a variety of cases, including models with non-perturbative gauge groups with both charged and uncharged localized matter. The underlying mathematics will be discussed further in a forthcoming publication
Quantum Gravity Bounds on N=1 Effective Theories in Four Dimensions
Full text linkWe propose quantum gravitational constraints on effective four-dimensional
theories with N=1 supersymmetry. These Swampland constraints arise by demanding
consistency of the worldsheet theory of a class of axionic, or EFT, strings
whose existence follows from the Completeness Conjecture of quantum gravity.
Modulo certain assumptions, we derive positivity bounds and quantization
conditions for the axionic couplings to the gauge and gravitational sector at
the two- and four-derivative level, respectively. We furthermore obtain general
bounds on the rank of the gauge sector in terms of the gravitational couplings
to the axions. We exemplify how these bounds rule out otherwise consistent
effective supergravity theories as theories of quantum gravity. Our derivations
of the quantum gravity bounds are tested and further motivated in concrete
string theoretic settings. In particular, this leads to a sharper version of
the bound on the gauge group rank in F-theory on elliptic four-folds with a
smooth base, which improves the known geometrical Kodaira bounds. We
furthermore provide a detailed derivation of the EFT string constraints in
heterotic string compactifications including higher derivative corrections to
the effective action and apply the bounds to M-theory compactifications on
manifolds.Comment: 84 pages, 2 figure
Fluxes in F-theory compactifications on genus-one fibrations
Full text linkWe initiate the construction of gauge fluxes in F-theory compactifications on genus-one fibrations which only have a multi-section as opposed to a section. F-theory on such spaces gives rise to discrete gauge symmetries in the effective action. We generalize the transversality conditions on gauge fluxes known for elliptic fibrations by taking into account the properties of the available multi-section. We test these general conditions by constructing all vertical gauge fluxes in a bisection model with gauge group SU(5) x Z(2). The non-abelian anomalies are shown to vanish. These flux solutions are dynamically related to fluxes on a fibration with gauge group SU(5) x U(1) by a conifold transition. Considerations of flux quantization reveal an arithmetic constraint on certain intersection numbers on the base which must necessarily be satisfied in a smooth geometry. Combined with the proposed transversality conditions on the fluxes these conditions are shown to imply cancellation of the discrete Z(2) gauge anomalies as required by general consistency considerations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
