Abstract: It is well known that a quantized two-dimensional Weyl fermion coupled to gravity spoils general covariance and breaks the covariant conservation of the energy-momentum tensor. In this brief article, we point out that the quantum conservation of the momentum can also fail in flat spacetime, provided the Weyl fermion is coupled to a time-varying homogeneous electric field. This signals a quantum anomaly of the space-translation symmetry, which has not been highlighted in the literature so far.

Abstract: Solutions to the backreaction equation in 1 + 1-dimensional semiclassical electrodynamics are obtained and analyzed when considering a time-varying homogeneous electric field initially generated by a classical electric current, coupled to either a quantized scalar field or a quantized spin-1/2 field. Particle production by way of the Schwinger effect leads to backreaction effects that modulate the electric field strength. Details of the particle production process are investigated along with the transfer of energy between the electric field and the particles. The validity of the semiclassical approximation is also investigated using a criterion previously implemented for chaotic inflation and, in an earlier form, semiclassical gravity. The criterion states that the semiclassical approximation will break down if any linearized gauge-invariant quantity constructed from solutions to the linear response equation, with finite nonsingular data, grows rapidly for some period of time. Approximations to homogeneous solutions of the linear response equation are computed and it is found that the criterion is violated when the maximum value, E-max, obtained by the electric field is of the order of the critical scale for the Schwinger effect, E-max similar to E-crit m(2)/q, where m is the mass of the quantized field and q is its electric charge. For these approximate solutions the criterion appears to be satisfied in the extreme limits qE(max)/m(2) << 1 and qE(max)/m(2) >> 1.

Abstract: We present a detailed study of the lowest-lying 1/2(-) and 3/2(-) Lambda Q resonances both in the heavy 2 2 quark (bottom and charm) and the strange sectors. We have paid special attention to the interplay between the constituent quark-model and chiral baryon-meson degrees of freedom, which are coupled using a unitarized scheme consistent with leading-order heavy quark symmetries. We show that the Lambda(b)(5912) [J(P) = 1/2(-)], Lambda(b)(5920) [J(P) = 3/2(-)] and the Lambda(c)(2625) [J(P) = 3/2-], and the Lambda(1520) [J(P) = 3/2(-)] admitting larger breaking corrections, are heavyquark spin-flavor siblings. They can be seen as dressed quark-model states with Sigma Q(()*()) pi molecular components of the order of 30%. The J(P)=1(-) Lambda(2595) has, however, a higher molecular 2 probability of at least 50%, and even values greater than 70% can be easily accommodated. This is because it is located almost on top of the threshold of the Sigma(c)pi pair, which largely influences its properties. Although the light degrees of freedom in this resonance would be coupled to spin-parity 1(-) as in the Lambda(b)(5912), Lambda(b)(5920) and Lambda(c)(2625), the Lambda(c)(2595) should not be considered as a heavy-quark spin-flavor partner of the former ones. We also show that the Lambda(1405) chiral two-pole pattern does not have analogs in the 1 – charmed and bottomed sectors, because the 2 N D-(*()) and N (B) over bar (()*()) channels do not play for heavy quarks the decisive role that the N (K) over bar does in the strange sector, and the notable influence of the bare quark-model states for the charm and bottom resonances. Finally, we predict the existence of two Lambda(b)(6070) and two Lambda(c)(2765) heavy-quark spin and flavor sibling odd parity states.

Abstract: We study f (R, T) theories of gravity, where T is the trace of the energy-momentum tensor T-mu v, with independent metric and affine connection (metric-affine theories). We find that the resulting field equations share a close resemblance with their metric-affine f(R) relatives once an effective energy-momentum tensor is introduced. As a result, the metric field equations are second-order and no new propagating degrees of freedom arise as compared to GR, which contrasts with the metric formulation of these theories, where a dynamical scalar degree of freedom is present. Analogously to its metric counterpart, the field equations impose the nonconservation of the energy-momentum tensor, which implies nongeodesic motion arid consequently leads to the appearance of an extra force. The weak field limit leads to a modified Poisson equation formally identical to that found in Eddington-inspired Born-Infeld gravity. Furthermore, the coupling of these gravity theories to perfect fluids, electromagnetic, and scalar fields, and their potential applications arc discussed.

Abstract: We study the structure and stability of traversable wormholes built as (spherically symmetric) thin shells in the context of Palatini f(R) gravity. Using a suitable junction formalism for these theories we find that the effective number of degrees of freedom on the shell is reduced to a single one, which fixes the equation of state to be that of massless stress-energy fields, contrary to the general relativistic and metric f(R) cases. Another major difference is that the surface energy density threading the thin shell, needed in order to sustain the wormhole, can take any sign and may even vanish, depending on the desired features of the corresponding solutions. We illustrate our results by constructing thin-shell wormholes by surgically grafting Schwarzschild space-times and show that these configurations are always linearly unstable. However, surgically joined Reissner-Nordstrom space-times allow for linearly stable, traversable thin-shell wormholes supported by a positive energy density provided that the (squared) mass-to-charge ratio, given by y = Q(2)/M-2, satisfies the constraint 1 < y < 9/8 (corresponding to overcharged Reissner-Nordstrom configurations having a photon sphere) and lies in a region bounded by specific curves defined in terms of the (dimensionless) radius of the shell x(0) = R/M.