Roberto Iengo

Indirect detection analysis: wino dark matter case study

We perform a multichannel analysis of the indirect signals for the Wino Dark Matter, including one-loop electroweak and Sommerfeld enhancement corrections. We derive limits from cosmic ray antiprotons and positrons, from continuum galactic and extragalactic diffuse γ-ray spectra, from the absence of γ-ray line features at the galactic center above 500 GeV in energy, from γ-rays toward nearby dwarf spheroidal galaxies and galaxy clusters, and from CMB power-spectra. Additionally, we show the future prospects for neutrino observations toward the inner Galaxy and from antideuteron searches. For each of these indirect detection probes we include and discuss the relevance of the most important astrophysical uncertainties that can impact the strength of the derived limits. We find that the Wino as a dark matter candidate is excluded in the mass range bellow 800 GeV from antiprotons and between 1.8 and 3.5 TeV from the absence of a γ-ray line feature toward the galactic center. Limits from other indirect detection probes confirm the main bulk of the excluded mass ranges.

Relic densities including Sommerfeld enhancements in the MSSM

We have developed a general formalism to compute Sommerfeld enhancement (SE) factors for a multi-state system of fermions, in all possible spin configurations and with generic long-range interactions. We show how to include such SE effects in an accurate calculation of the thermal relic density for WIMP dark matter candidates. We apply the method to the MSSM and perform a numerical study of the relic abundance of neutralinos with arbitrary composition and including the SE due to the exchange of the W and Z bosons, photons and Higgses. We find that the relic density can be suppressed by a factor of a few in a sizable region of the parameter space, mostly for Wino-like neutralino with mass of a few TeV, and up to an order of magnitude close to a resonance.

Sommerfeld enhancement: general results from field theory diagrams

Assuming that two incoming annihilating particles interact by exchanging a generally massive attractive vector (or scalar) boson, we find, by taking the non-relativistic limit of the field theory ladder diagrams, that the complete annihilation amplitude A is equal to: the convolution of a solution of the Schroedinger equation (including the attractive potential) with the Fourier transform of the bare (i.e. ignoring the attraction) annihilation amplitude A0. The main novelty is that A0 can be completely arbitrary. For a Coulomb potential we find analytically the enhancement for the l-partial-wave cross-section, e.g. the P wave enhancement 2π(α/v)3 (v relative velocity), for a Yukawa potential we describe a simple algorithm and give numerical results showing an important P wave enhancement with a resonant pattern.

Two-loop computation of the four-particle amplitude in heterotic string theory

Abstract By using the hyperelliptic formalism we obtain an explicit integral formulafor the four-massless-particle scattering amplitude at two loops in heterotic string theory. We verify the main properties and in particular its finiteness. The corresponding expression for type II superstrings is also given.

Modular invariance and the two-loop vanishing of the cosmological constant

Abstract With a moduli independent choice of super-Beltrami differentials, we show, by using the genus-two hyperelliptic formalism, that the requirement of modular invariance determines completely the two-loop amplitudes of the heterotic string theory for arbitrary external legs and that the cosmological constant is zero pointwise in moduli space.

The one-loop and Sommerfeld electroweak corrections to the Wino dark matter annihilation

A bstractWe compute the present-day Wino dark matter annihilation cross-section including the one-loop radiative corrections together with the fully treated electroweak Sommerfeld effect. We discuss what is the consistent way of incorporating these two corrections simultaneously and why simply using the running coupling constants values at the Winomass scale is not correct. The results show that up to a few TeV scale the full one-loop computation makes the cross-section smaller up to about 30% with respect to the Sommerfeld enhanced tree level result and are considerably larger than the tree or one-loop level without the Sommerfeld effect.

Anyon quantum mechanics and Chern-Simons theory

Particles of fractional statistics living on a two-dimensional surface - anyons - are of importance for the theory of the quantum Hall effect and for the possibility of a new mechanism of superconductivity. Anyons can also be described as ordinary bosons or fermions interacting with a topological Chern-Simons (CS) gauge field. We review the peculiar quantum mechanical properties of a system of nonrelativistic anyons, described in the first-quantization framework. Boundary conditions play a relevant role in this problem and we review, accordingly, various cases: the infinite plane displaying mainly the local properties, the sphere which can also be seen as the compactification of a plane and is suited for the investigation of rotational invariance and angular momentum, and the torus, i.e., the case of periodic boundary conditions, which is the surface compatible with translational invariance and is thus suited for the analysis of linear momentum. In this last case, topological modes of the CS gauge field appear as dynamical variables and we review the non-trivial quantum mechanics of the system of CS modes coupled to the nonrelativistic particles. Periodic boundary conditions are particularly important for investigating the possibility of persistent dissipationless superconducting currents and, accordingly, we present relevant physical applications.

Explicit modular invariant two-loop superstring amplitude relevant for R-4

In this note we derive an explicit modular invariant formula for the two loop 4-point amplitude in superstring theory in terms of a multiple integral (7 complex integration variables) over the complex plane which is shown to be convergent. We consider in particular the case of the leading term for vanishing momenta of the four graviton amplitude, which would correspond to the two-loop correction of the R-4 term in the effective Action. The resulting expression is not positive definite and could be zero, although we cannot see that it vanishes.

Multiloop divergences in the closed bosonic string theory

The structure of the divergences in the multiloop vacuum diagrams for the closed bosonic strings in the framework of the Polyakov covariant formalism is discussed. It is found, by an explicit computation, that all the divergences in the theory may be interpreted as due to tadpole diagrams in which the dilaton goes into the vacuum.

Notes on the non-renormalization theorem in superstring theories

Abstract The non-renormalization theorem is verified at two loops by explicit computation using the hyperelliptic formalism. A set of identities is found which leads to a great simplification of the calculation of the four-particle amplitude at two loops.