(Non-)BPS bound states and D-brane instantons

We study non-perturbative effects in four-dimensional N=1 supersymmetric orientifold compactifications due to D-brane instantons which are generically not invariant under the orientifold projection. We show that they can yield superpotential contributions via a multi-instanton process at threshold. Some constituents of this configuration form bound states away from the wall of marginal stability which can decay in other regions of moduli space. A microscopic analysis reveals how contributions to the superpotential are possible when new BPS states compensate for their decay. We study this concretely for D2-brane instantons along decaying special Lagrangians in Type IIA and for D5-branes instantons carrying holomorphic bundles in Type I theory.Comment: 39 pages, 4 tables, 2 figures; v2: Equ. (20) corrected, related discussion adjusted, 1 reference added; v3: JHEP version with more refs adde

Firm Performance and Insider Trading: A Comparison Between Voluntary and Involuntary Bankruptcy Filings

We compare the financial performance and insider trading characteristics of firms finding for voluntary bankruptcy with firms that are petitioned into bankruptcy involuntarily by their creditors. We find that shareholders of firms filing for voluntary bankruptcy experience significantly greater losses around the bankruptcy announcement than shareholders of involuntary filers. We also find that insiders of firms filing voluntarily are net sellers of their firm\u27s shares in the years leading up to bankruptcy, vs. net buying by insiders of involuntary filers. Moreover, firms filing voluntary bankruptcy successfully reorganize less frequently and liquidate more frequently titan firms that file involuntary bankruptcy. These findings are consistent with the idea that corporate insiders in firms filing for voluntary bankruptcy have reduced incentives to maximize shareholder welfare throughout the Chapter 11 process compared with insiders of firms tit at are petitioned into bankruptcy by their creditors

Non-perturbative Yukawa Couplings from String Instantons

Non-perturbative D-brane instantons can generate perturbatively absent though phenomenologically relevant couplings for Type II orientifold compactifications with D-branes. We discuss the generation of the perturbatively vanishing SU(5) GUT Yukawa coupling of type 10 10 5_H. Moreover, for a simple globally consistent intersecting D6-brane model, we discuss the generation of mass terms for matter fields. This can serve as a mechanism for decoupling exotic matter.Comment: 4 pages, 2 tables, 2 figure