New Limits on the Dark Matter Lifetime from Dwarf Spheroidal Galaxies using Fermi-LAT

Dwarf spheroidal galaxies (dSphs) are promising targets for the indirect detection of dark matter through gamma-ray emission due to their proximity, lack of astrophysical backgrounds and high dark matter density. They are often used to place restrictive bounds on the dark matter annihilation cross section. In this paper, we analyze six years of {\it Fermi}-LAT gamma-ray data from 19 dSphs that are satellites of the Milky Way, and derive from a stacked analysis of 15 dSphs, robust 95\% confidence level lower limits on the dark matter lifetime for several decay channels and dark matter masses between $\sim 1$GeV and $10$TeV. Our findings are based on a bin-by-bin maximum likelihood analysis treating the J-factor as a nuisance parameter using PASS 8 event-class. Our constraints from this ensemble are among the most stringent and solid in the literature, and competitive with existing ones coming from the extragalactic gamma-ray background, galaxy clusters, AMS-02 cosmic ray data, Super-K and ICECUBE neutrino data, while rather insensitive to systematic uncertainties. In particular, among gamma-ray searches, we improve existing limits for dark matter decaying into $\bar{b}b$, ($\mu^+\mu^-$) for DM masses below $\sim 30\, (200)$~GeV, demonstrating that dSphs are compelling targets for constraining dark matter decay lifetimes.Comment: 4 figures, 7 pages. Inclusion of PASS 8 event-class, maximum likelihood analysis and a new figure concerning Reticulum-II. Accepted in Physical Review

Entanglement in fermionic chains with finite range coupling and broken symmetries

We obtain a formula for the determinant of a block Toeplitz matrix associated with a quadratic fermionic chain with complex coupling. Such couplings break reflection symmetry and/or charge conjugation symmetry. We then apply this formula to compute the Renyi entropy of a partial observation to a subsystem consisting of $X$ contiguous sites in the limit of large $X$. The present work generalizes similar results due to Its, Jin, Korepin and Its, Mezzadri, Mo. A striking new feature of our formula for the entanglement entropy is the appearance of a term scaling with the logarithm of the size of $X$. This logarithmic behaviour originates from certain discontinuities in the symbol of the block Toeplitz matrix. Equipped with this formula we analyse the entanglement entropy of a Dzyaloshinski-Moriya spin chain and a Kitaev fermionic chain with long range pairing.Comment: 27 pages, 5 figure

Localization in the Rindler Wedge

One of the striking features of QED is that charged particles create a coherent cloud of photons. The resultant coherent state vectors of photons generate a non-trivial representation of the localized algebra of observables that do not support a representation of the Lorentz group: Lorentz symmetry is spontaneously broken. We show in particular that Lorentz boost generators diverge in this representation, a result shown also in [1] (See also [2]). Localization of observables, for example in the Rindler wedge, uses Poincar\'e invariance in an essential way [3]. Hence in the presence of charged fields, the photon observables cannot be localized in the Rindler wedge. These observations may have a bearing on the black hole information loss paradox, as the physics in the exterior of the black hole has points of resemblance to that in the Rindler wedge.Comment: 11 page

On the M\"obius transformation in the entanglement entropy of fermionic chains

There is an intimate relation between entanglement entropy and Riemann surfaces. This fact is explicitly noticed for the case of quadratic fermionic Hamiltonians with finite range couplings. After recollecting this fact, we make a comprehensive analysis of the action of the M\"obius transformations on the Riemann surface. We are then able to uncover the origin of some symmetries and dualities of the entanglement entropy already noticed recently in the literature. These results give further support for the use of entanglement entropy to analyse phase transition.Comment: 29 pages, 5 figures. Final version published in JSTAT. Two new figures. Some comments and references added. Typos correcte

A Review of Tools for Project Financial Assessments

Governments not always have the funds to build transport and other infrastructure projects that are economically justified and environmentally and socially sound. Under certain circumstances, projects meeting such conditions can be implemented by involving private financing, through public-private partnerships (PPP), which is a means to get projects completed by leveraging scarce public resources. In a PPP project, the sources of revenue to the private partner (or concessionaire) may include (i) the users of the facility (e.g., road tolling), (ii) the government (e.g. through availability payments, capital grants and shadow tolls), and (iii) both users and government, which is usually called a hybrid concession. As a key step in considering attracting private investors for such projects, decision makers and practitioners need to assess their financial viability, an endeavor that can be greatly facilitated by relatively simple tools now available. This paper reviews and provides case studies of two existing tools for assessing the financial viability of: (i) hybrid road PPP projects, which involve both tolls and availability payments; and (ii) output- and performance-based road contracts (OPBRC), which involves payments by the government. The main output generated by both models include the project's internal rate of return, equity internal rate of return, annual debt service coverage ratio and the present value of the government's cash flow