The twisted open string partition function and Yukawa couplings

We use the operator formalism to derive the bosonic contribution to the twisted open string partition function in toroidal compactifications. This amplitude describes, for instance, the planar interaction between g+1 magnetized or intersecting D-branes. We write the result both in the closed and in the open string channel in terms of Prym differentials on the appropriate Riemann surface. Then we focus on the g=2 case for a 2-torus. By factorizing the twisted partition function in the open string channel we obtain an explicit expression for the 3-twist field correlator, which is the main ingredient in the computation of Yukawa couplings in D-brane phenomenological models. This provides an alternative method for computing these couplings that does not rely on the stress-energy tensor technique.Comment: 32 pages, 5 figures, Latex; v2: typos correcte

Intersecting Brane World from Type I Compactification

We elaborate that general intersecting brane models on orbifolds are obtained from type I string compactifications and their T-duals. Symmetry breaking and restoration occur via recombination and parallel separation of branes, preserving supersymmetry. The Ramond-Ramond tadpole cancelation and the toron quantization constrain the spectrum as a branching of the adjoints of SO(32), up to orbifold projections. Since the recombination changes the gauge coupling, the single gauge coupling of type I could give rise to different coupling below the unification scale. This is due to the nonlocal properties of the Dirac-Born-Infeld action. The weak mixing angle sin^2 theta_W = 3/8 is naturally explained by embedding the quantum numbers to those of SO(10).Comment: 31 pages, 5 figure

Beyond shared socioeconomic pathways (SSPs) and representative concentration pathways (RCPs): climate policy implementation scenarios for Europe, the US and China

The 2015 Paris Agreement is falling short of its aspirations, as signatory countries are struggling to implement the policies required to meet the targets. The global scenario framework formed by the Shared Socioeconomic Pathways (SSPs) and the Representative Concentration Pathways (RCPs) places little emphasis on the dynamics of climate policy implementation. Social science approaches to understanding these dynamics are not well-integrated into climate scenario research. We apply an implementation research approach to analyse the transition to clean energy in the US and China, as well as two examples from Europe–Germany and Spain–which have shown markedly diverging implementation trajectories. We propose four implementation scenarios (ISs) for clean energy worldwide which relate to different configurations of actors in the policy system. These are: (1) Civil Society Takes Control (IS1)–where ideologically opposed governments are marginalised by citizens and forward-thinking investors; (2) Strong-arm Transition (IS2)–where a single party state drives the transition without the involvement of civil society; (3) Systemic Limits (IS3)–which highlights the need to focus on the whole energy system, not just renewables; and (4) Renewable Austerity (IS4)–where an economic downturn offers powerful anti-transition actors the opportunity to advocate removal of support for climate mitigation, as they did after the 2007–2008 financial crisis. This scenario could be repeated as countries seek to recover from the Covid-19 pandemic. Our study offers a framework for structured analysis of real-world constraints faced by implementing actors, which we argue is urgently needed to help national and international policy makers achieve climate goals. Key policy insights The world is struggling to implement the Paris Agreement, partly because the complex dynamics of climate policy implementation are poorly understood. Social science approaches to understanding these dynamics are not well-integrated into climate scenario research. Implementation research focussing on the actors and context provides a useful framework for analysis of implementation efforts from major global carbon emitters. The approach offers new and distinctive scenario narratives that go beyond Representative Concentration Pathways (RCPs) and Shared Socioeconomic Pathways (SSPs). These new scenarios can help policy makers evaluate likely outcomes of climate policy implementation based on information about actors and context. © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group

Chiral N=1 4d Orientifolds with D-branes at Angles

D6-branes intersecting at angles allow for phenomenologically appealing constructions of four dimensional string theory vacua. While it is straightforward to obtain non-supersymmetric realizations of the standard model, supersymmetric and stable models with three generations and no exotic chiral matter require more involved orbifold constructions. The T^6/(Z_4 x Z_2 x OmegaR) case is discussed in detail. Other orbifolds including fractional D6-branes are treated briefly.Comment: Invited brief review, 16 pages, 2 figures; references adde

Intersecting Brane Worlds at One Loop

We develop techniques for one-loop diagrams on intersecting branes. The one-loop propagator of chiral intersection states on D6 branes is calculated exactly and its finiteness is shown to be guaranteed by RR tadpole cancellation. The result is used to demonstrate the expected softening of power law running of Yukawa couplings at the string scale. We also develop methods to calculate arbitrary N-point functions at one-loop, including those without gauge bosons in the loop. These techniques are also applicable to heterotic orbifold models.Comment: 35 pages, 3 figures; added reference, corrected typos, JHEP styl

TeV-Scale Z' Bosons from D-branes

Generic D-brane string models of particle physics predict the existence of extra U(1) gauge symmetries beyond hypercharge. These symmetries are not of the E_6 class but rather include the gauging of Baryon and Lepton numbers as well as certain Peccei-Quinn-like symmetries. Some of the U(1)'s have triangle anomalies, but they are cancelled by a Green-Schwarz mechanism. The corresponding gauge bosons typically acquire a mass of order the string scale M_S by combining with two-index antisymmetric fields coming from the closed string sector of the theory. We argue that in string models with a low string scale M_S proportional to 1-10 TeV, the presence of these generic U(1)'s may be amenable to experimental test. Present constraints from electroweak precision data already set important bounds on the mass of these extra gauge bosons. In particular, for large classes of models, rho-parameter constraints imply M_S >= 1.5 TeV. In the present scheme some fraction of the experimentally measured Z^0 mass would be due not to the Higgs mechanism, but rather to the mixing with these closed string fields. We give explicit formulae for recently constructed classes of intersecting D6- and D5-brane models yielding the Standard Model (SM) fermion spectrum.Comment: 46 pages, LaTeX, JHEP.cls, 21 Figures. minor correction

Computing Yukawa Couplings from Magnetized Extra Dimensions

We compute Yukawa couplings involving chiral matter fields in toroidal compactifications of higher dimensional super-Yang-Mills theory with magnetic fluxes. Specifically we focus on toroidal compactifications of D=10 super-Yang-Mills theory, which may be obtained as the low-energy limit of Type I, Type II or Heterotic strings. Chirality is obtained by turning on constant magnetic fluxes in each of the 2-tori. Our results are general and may as well be applied to lower D=6,8 dimensional field theories. We solve Dirac and Laplace equations to find out the explicit form of wavefunctions in extra dimensions. The Yukawa couplings are computed as overlap integrals of two Weyl fermions and one complex scalar over the compact dimensions. In the case of Type IIB (or Type I) string theories, the models are T-dual to (orientifolded) Type IIA with D6-branes intersecting at angles. These theories may have phenomenological relevance since particular models with SM group and three quark-lepton generations have been recently constructed. We find that the Yukawa couplings so obtained are described by Riemann theta-functions, which depend on the complex structure and Wilson line backgrounds. Different patterns of Yukawa textures are possible depending on the values of these backgrounds. We discuss the matching of these results with the analogous computation in models with intersecting D6-branes. Whereas in the latter case a string computation is required, in our case only field theory is needed.Comment: 73 pages, 9 figures. Using JHEP3.cls. Typos and other minor corrections fixed. References adde

Orbifold resolutions with general profile

A very general class of resolved versions of the C/Z_N, T^2/Z_N and S^1/Z_2 orbifolds is considered and the free theory of 6D chiral fermions studied on it. As the orbifold limit is taken, localized 4D chiral massless fermions are seen to arise at the fixed points. Their number, location and chirality is found to be independent on the detailed profile of the resolving space and to agree with the result of hep-th/0409229, in which a particular resolution was employed. As a consistency check of the resolution procedure, the massive equation is numerically studied. In particular, for S^1/Z_2, the "resolved" mass--spectrum and wave functions in the internal space are seen to correctly reproduce the usual orbifold ones, as the orbifold limit is taken.Comment: 28 pages, 3 figures, typos corrected, references adde

Effects of oligomer toxicity, fibril toxicity and fibril spreading in synucleinopathies; 35244787

Protein misfolding is a general hallmark of protein deposition diseases, such as Alzheimer’s disease or Parkinson’s disease, in which different types of aggregated species (oligomers, protofibrils and fibrils) are generated by the cells. Despite widespread interest, the relationship between oligomers and fibrils in the aggregation process and spreading remains elusive. A large variety of experimental evidences supported the idea that soluble oligomeric species of different proteins might be more toxic than the larger fibrillar forms. Furthermore, the lack of correlation between the presence of the typical pathological inclusions and disease sustained this debate. However, recent data show that the ß-sheet core of the a-Synuclein (aSyn) fibrils is unable to establish persistent interactions with the lipid bilayers, but they can release oligomeric species responsible for an immediate dysfunction of the recipient neurons. Reversibly, such oligomeric species could also contribute to pathogenesis via neuron-to-neuron spreading by their direct cell-to-cell transfer or by generating new fibrils, following their neuronal uptake. In this Review, we discuss the various mechanisms of cellular dysfunction caused by aSyn, including oligomer toxicity, fibril toxicity and fibril spreading. © 2022, The Author(s)