Invariant solutions to the Strominger system and the heterotic equations of motion

We construct many new invariant solutions to the Strominger system with respect to a 2-parameter family of metric connections $\nabla^{\varepsilon,\rho}$ in the anomaly cancellation equation. The ansatz $\nabla^{\varepsilon,\rho}$ is a natural extension of the canonical 1-parameter family of Hermitian connections found by Gauduchon, as one recovers the Chern connection $\nabla^{c}$ for $({\varepsilon,\rho})=(0,\frac12)$, and the Bismut connection $\nabla^{+}$ for $({\varepsilon,\rho})=(\frac12,0)$. In particular, explicit invariant solutions to the Strominger system with respect to the Chern connection, with non-flat instanton and positive $\alpha'$ are obtained. Furthermore, we give invariant solutions to the heterotic equations of motion with respect to the Bismut connection. Our solutions live on three different compact non-K\"ahler homogeneous spaces, obtained as the quotient by a lattice of maximal rank of a nilpotent Lie group, the semisimple group SL(2,$\mathbb{C}$) and a solvable Lie group. To our knowledge, these are the only known invariant solutions to the heterotic equations of motion, and we conjecture that there is no other such homogeneous space admitting an invariant solution to the heterotic equations of motion with respect to a connection in the ansatz $\nabla^{\varepsilon,\rho}$.Comment: 27 pages, 3 figure

The ascending central series of nilpotent Lie algebras with complex structure

We obtain several restrictions on the terms of the ascending central series of a nilpotent Lie algebra $\mathfrak g$ under the presence of a complex structure $J$. In particular, we find a bound for the dimension of the center of $\mathfrak g$ when it does not contain any non-trivial $J$-invariant ideal. Thanks to these results, we provide a structural theorem describing the ascending central series of 8-dimensional nilpotent Lie algebras $\mathfrak g$ admitting this particular type of complex structures $J$. Since our method is constructive, it allows us to describe the complex structure equations that parametrize all such pairs $(\mathfrak g, J)$.Comment: 28 pages, 1 figure. To appear in Trans. Amer. Math. So

Symplectically harmonic cohomology of nilmanifolds

This paper can be considered as an extension to our paper [On symplectically harmonic forms on six-dimensional nilmanifolds, Comment. Math. Helv. 76 (2001), n 1, 89-109]. Also, it contains a brief survey of recent results on symplectically harmonic cohomology.Comment: 18 page

The Magnetic Properties of Heating Events on High-Temperature Active Region Loops

Understanding the relationship between the magnetic field and coronal heating is one of the central problems of solar physics. However, studies of the magnetic properties of impulsively heated loops have been rare. We present results from a study of 34 evolving coronal loops observed in the Fe XVIII line component of AIA/SDO 94 A filter images from three active regions with different magnetic conditions. We show that the peak intensity per unit cross-section of the loops depends on their individual magnetic and geometric properties. The intensity scales proportionally to the average field strength along the loop ($B_{avg}$) and inversely with the loop length ($L$) for a combined dependence of $(B_{avg}/L)^{0.52\pm0.13}$. These loop properties are inferred from magnetic extrapolations of the photospheric HMI/SDO line-of-sight and vector magnetic field in three approximations: potential and two Non Linear Force-Free (NLFF) methods. Through hydrodynamic modeling (EBTEL model) we show that this behavior is compatible with impulsively heated loops with a volumetric heating rate that scales as $\epsilon_H\sim B_{avg}^{0.3\pm0.2}/L^{0.2\pm^{0.2}_{0.1}}$.Comment: Astrophysical Journal, in pres

The Effects of Vouchers on Academic Achievement: Evidence from Chile’s Conditional Voucher Program Juan A. Correa David Inostroza Francisco Parro Loreto Reyes Gabriel Ugarte Universidad Andrés Bello Marzo

Indexación: UNAB JEL Classi cation: H4; I2Abstract We use data from Chile's conditional voucher program to test the e ects of vouchers on academic achievement. Conditional vouchers have delivered extra resources to low-income, vulnerable students since 2008. Moreover, under this scheme, additional resources are contingent on the completion of speci c scholastic goals. Using a di erence-in-di erences approach, we nd a positive and signi cant e ect of vouchers on standardized test scores. Additionally, our results highlight the importance of conditioning the delivery of resources to some speci c academic goals when frictions exist in the education market

The GRB 030328 host: another case of a blue starburst galaxy

We present for the first time the detection of the GRB 030328 host galaxy in four optical bands equivalent to UBRI. The host galaxy spectral energy distribution is consistent with a low extinction (E(B-V) < 0.21) starburst galaxy. The restframe B-band magnitude of the host is M_B ~ -20.4Comment: 4 pages, 2 figures, accepted for publication in Il nuovo cimento (4th Workshop Gamma-Ray Bursts in the Afterglow Era, Rome, 18-22 October 2004

On non-Kähler compact complex manifolds with balanced and Astheno-Kähler metrics [Sur les variétés compactes complexes non Kähler avec des métriques équilibrées et Asthéno-Kähler]

In this note, we construct, for every n=4, a non-Kähler compact complex manifold X of complex dimension n admitting a balanced metric and an astheno-Kähler metric, which is in addition k-th Gauduchon for any 1<=k<=n-1

On potential information asymmetries in long-term care insurance: a simulation study using data from Switzerland

The long-term care insurance (LTCI) market in Switzerland is still in a very early development stage. In this work, we make use of a representative sample of the Swiss population to simulate the likely effects of previously discovered information asymmetries in the LTCI market. By resorting to LTCI preferences of potential customers, and using Monte Carlo simulations, we provide estimations of the expected probability and duration of dependence indicators. Thereby, we compare the frequency and severity of the sub-population that has shown interest in LTCI with the rest in different mortality scenarios. While in the Swiss demographic context, individuals have a high probability to experience loss of autonomy in their lifetime, we do not find evidence to believe that those interested in LTCI coverage are so based on privileged information about them being at greater risk. In fact, we discover that most people are not aware of their own risk to lose autonomy, which makes potential adverse selection in the LTCI market rather difficult