119297660
Primordial black holes and the observed Galactic 511 keV line
Abstract The observed 511 keV line from the Galactic Bulge is a real challenge for theoretical astrophysics: despite a lot of suggested mechanisms, there is still no convincing explanation and the origin of the annihilated positrons remains unknown. Here we discuss the possibility that a population of slowly evaporating primordial black holes with the mass around 10 16 –10 17 g ejects (among other particles) low-energy positrons into the Galaxy. In addition to positrons, we have also calculated the spectrum and number density of photons and neutrinos produced by such black holes and found that the photons are potentially observable in the near future, while the neutrino flux is too weak and below the terrestrial and extra-terrestrial backgrounds. Depending on their mass distribution, such black holes could make a small fraction or the whole cosmological dark matter.
118687281
Hadronic D and D(s) Meson Decays
We provide a comprehensive review of hadronic decays of D and D_s mesons. We discuss current theoretical and experimental challenges and successes in understanding of hadronic transitions of those mesons. A brief overview of the theoretical and experimental tools are given before discussing the absolute branching fractions for D and D_s mesons. Cabibbo suppressed and rare hadronic decays are discussed and compared with theory before discussing our understanding of hadronic multibody decays.
35942201
Is B-->Xs gamma equal to b-->s gamma ? Spectator contributions to rare inclusive B decays.
In $B \to X_s \gamma $ there are perturbative $QCD$ corrections at order $\alpha_s$ not only to the single quark line process $ b \to s \gamma$ but also coming from a set of diagrams where the weak interaction vertex involves a gluon which interacts with the spectator quark in the B hadron. We discuss the impact of the full set of these diagrams. These can influence the decay rate and also the line shape of the photon spectrum as they favor a softer photon energy than does the pure spectator decay $b \to s \gamma$. A subset of these diagrams generate differences in the decay rates for charged and neutral B's , $B^+ \to X_s \gamma$ vs. $B^0 \to X_s \gamma$ which can be searched for experimentally, although our calculation indicates that the effect will be hard to observe. Bound state effects turn out to be required to give rise to spectator corrections to the decay rate at order $\alpha_s$. The resulting contribution to the total rate is rather small (of about $5 \% $ ), although the effect is somewhat larger on portions of the photon spectrum.
117901603
X(3872) in effective field theory
We consider the implications from the possibility that the recently observed state X(3872) is a meson‐antimeson molecule. We write an effective Lagrangian consistent with the heavy‐quark and chiral symmetries needed to describe X(3872) and study its properties.
14759150
Heavy meson molecules in effective field theory
We consider the implications from the possibility that the recently observed state X(3872) is a meson-antimeson molecule. We write an effective Lagrangian consistent with the heavy-quark and chiral symmetries needed to describe X(3872). We explore the consequences of the assumption that X(3872) is a molecular bound state of D�0 and D0 mesons for the existence of bound states in the D0D0 and D�0D �0
14564633
CHARM MIXING IN THE STANDARD MODEL AND BEYOND
Quantum mechanical meson-antimeson oscillations are sensitive to heavy degrees of freedom which propagate in the underlying mixing amplitudes. Comparing observed meson mixing with predictions of the Standard Model (SM), modern experimental studies would be able to constrain models of New Physics (NP). Yet, extensive precission data from B-factories and the Tevatron collider show that the large SM mixing succesfully describes all available experimental data in Bd and Bs oscillations. The only flavor oscillation not yet observed is that of the charmed meson D, where SM mixing is very small and the NP component can stand out. This situation is an exact opposite to what happens in the B system, where B − B0 mixing measurements are used to constrain top quark couplings. Together with the one loop Standard Model effects NP effects can contribute to ∆C = 1 (decays) or ∆C = 2 (mixing) transitions. In the case of D −D0 mixing these operators generate contributions to the effective operators that change D state into D0 state, leading to the mass eigenstates |D1,2〉 = p|D〉 ± q|D〉, (1)
2496873
Complete low-energy effective action in N=4 SYM: A Direct N=2 supergraph calculation
Using the covariant N=2 harmonic supergraph techniques we calculate the one-loop low-energy effective action of N=4 super-Yang–Mills theory in Coulomb branch with gauge group SU(2) spontaneously broken down to U(1). The full dependence of the low-energy effective action on both the hypermultiplet and gauge fields is determined. The direct quantum calculation confirms the correctness of the exact N=4 SYM low-energy effective action derived in hep-th/0111062 on the purely algebraic ground by invoking a hidden N=2 supersymmetry which completes the manifest N=2 one to N=4. Our results provide an exhaustive solution to the problem of finding out the exact completely N=4 supersymmetric low-energy effective action for the theory under consideration.
118356440
On the effective potential in higher-derivatives superfield theories
Abstract We study the one-loop quantum corrections for higher-derivative superfield theories, generalizing the approach for calculating the superfield effective potential. In particular, we calculate the effective potential for two versions of higher-derivative chiral superfield models. We point out that the equivalence of the higher-derivative theory for the chiral superfield and the one without higher derivatives but with an extended number of chiral superfields occurs only when the mass term is contained in the general Lagrangian. The presence of divergences can be taken as an indication of that equivalence.
119261988
Horava-Lifshitz modifications of the Casimir effect
We study the modifications induced by spacetime anisotropy on the Casimir effect in the case of two parallel plates. Non-perturbative and perturbative regimes are analyzed. In the first case, the Casimir force either vanishes or it reverses its direction which, in any case, makes the proposal untenable. On the other hand, the perturbative model enables us to incorporate appropriately the effects of spacetime anisotropy.
119127214
On the aether-like Lorentz-breaking action for the electromagnetic field
We study the generation of aether-like Lorentz-breaking actions in three, four and five dimensions via an appropriate Lorentz-breaking coupling of electromagnetic and spinor fields. Special attention is given to the four-dimensional case where we discuss the issue of ambiguities.
119224824
On the effective potential for Horava-Lifshitz-like theories
The Horava-Lifshitz (HL) approach [1] has recently acquired a great scientific attention. This approach is characterized by an essential asymmetry between space and time coordinates (space-time anisotropy): the equations of motion of the theory are invariant under the rescaling x → bx, t → bt, where z, the critical exponent, is a number characterizing its ultraviolet behaviour. The main reason for it is that for the HL-like reformulation of the known field theory models with a nontrivial critical exponent z > 1 leads to an improvement of the renormalization of these models. In particular, the four-dimensional gravity becomes renormalizable at z = 3. Different issues related to the HL gravity, including its cosmological aspects [2], exact solutions [3], black holes [4] were considered in a number of papers. At the same time, the study of the impacts of the HL extension to other field theories is a very interesting problem. Some aspects of the HL generalizations for the gauge field theories were presented in [5]. Renormalizability of the scalar field theory models with space-time anisotropy has been discussed in details in [6]. The four-fermion HL-like theory has been studied in [7]. The Casimir effect for the HL-like scalar field theory has been considered in [8]. In [9], the HL modifications of the CP were studied. The possibility of restoration of the Lorentz symmetry in the theories with the space-time anisotropy is discussed in [5, 10]. It is well known that the effective potential is a key object in the quantum field theory useful for studying many of its aspects. Some interesting results for the HL-like theories have been obtained in the papers [11, 12] where the effective potential for the φ and the Liouville-