CvetiÄ, Mirjam

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Now showing 1 - 10 of 11
  • Publication
    D-Instanton Generated Dirac Neutrino Masses
    (2008-09-18) Cvetič, Mirjam; Langacker, Paul
    We present a stringy mechanism to generate Dirac neutrino masses by D-instantons in an experimentally relevant mass scale without fine-tuning. Within type IIA string theory with intersecting D6-branes, we spell out specific conditions for the emergence of such couplings and provide a class of supersymmetric local SU(5) grand unified models, based on the Z2 × Z'2 orientifold compactification, where perturbatively absent Dirac neutrino masses can be generated by D2-brane instantons in the experimentally observed mass regime, while Majorana masses remain absent, thus providing an intriguing mechanism for the origin of small neutrino masses due to nonperturbative stringy effects.
  • Publication
    Computation of D-brane instanton induced superpotential couplings: Majorana masses from string theory
    (2007-10-18) Cvetič, Mirjam; Richter, Robert; Weigand, Timo
    We perform a detailed conformal field theory analysis of D2-brane instanton effects in four-dimensional type IIA string vacua with intersecting D6-branes. In particular, we explicitly compute instanton induced fermion two-point couplings which play the role of perturbatively forbidden Majorana mass terms for right-handed neutrinos or MSSM μ terms. These results can readily be extended to higherdimensional operators. In concrete realizations of such nonperturbative effects, the Euclidean D2-branehas to wrap a rigid, supersymmetric cycle with strong constraints on the zero-mode structure. Their implications for type IIA compactifications on the T6/ (Z2 X Z2) orientifold with discrete torsion are analyzed. We also construct a local supersymmetric GUT-like model allowing for a class of Euclidean D2-branes whose fermionic zero modes meet all the constraints for generating Majorana masses in the phenomenologically allowed regime. Together with perturbatively realized Dirac masses, these nonperturbative couplings give rise to the seesaw mechanism.
  • Publication
    Non-Abelian Black Holes in D = 5 maximal gauged supergravity
    (2010-02-12) Cvetič, Mirjam; Lü, H.; Pope, C. N.
    We investigate static non-Abelian black hole solutions of anti–de Sitter (AdS) Einstein-Yang-Millsdilaton gravity, which is obtained as a consistent truncation of five-dimensional maximal gauged supergravity. If the dilaton is (consistently) set to zero, the remaining equations of motion, with a spherically-symmetric ansatz, may be derived from a superpotential. The associated first-order equations admit an explicit solution supported by a non-Abelian SU(2) gauge potential, which has a logarithmically growing mass term. In an extremal limit the horizon geometry becomes AdS2 X S3. If the dilaton is also excited, the equations of motion cannot easily be solved explicitly, but we obtain the asymptotic form of the more general non-Abelian black holes in this case. An alternative consistent truncation, in which the Yang-Mills fields are set to zero, also admits a description in terms of a superpotential. This allows us to construct explicit wormhole solutions (neutral spherically-symmetric domain walls). These solutions may be generalized to dimensions other than five.
  • Publication
    Nonperturbative Yukawa Couplings from String Instantons
    (2008-02-15) Blumenhagen, Ralph; Cvetič, Mirjam; Lüst, Dieter; Richter, Robert; Weigand, Timo
    Nonperturbative 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 5H). 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.
  • Publication
    Black Hole Enthalpy and an Entropy Inequality for the Thermodynamic Volume
    (2011-07-20) Cvetič, Mirjam; Gibbons, G. W.; Kubizňák, D.; Pope, C. N.
    In a theory where the cosmological constant Λ or the gauge coupling constant g arises as the vacuum expectation value, its variation should be included in the first law of thermodynamics for black holes. This becomes dE=TdS+ΩidJi+ΦαdQα+ΘdΛ, where E is now the enthalpy of the spacetime, and Θ, the thermodynamic conjugate of Λ, is proportional to an effective volume V=-16πΘ/D-2 “inside the event horizon.” Here we calculate Θ and V for a wide variety of D-dimensional charged rotating asymptotically anti-de Sitter (AdS) black hole spacetimes, using the first law or the Smarr relation. We compare our expressions with those obtained by implementing a suggestion of Kastor, Ray, and Traschen, involving Komar integrals and Killing potentials, which we construct from conformal Killing-Yano tensors. We conjecture that the volume V and the horizon area A satisfy the inequality R≡ ((D-1)V/AD-2)1/(D-1)(AD-2/A)1/(D-2)≥1, where AD-2 is the volume of the unit (D-2) sphere, and we show that this is obeyed for a wide variety of black holes, and saturated for Schwarzschild-AdS. Intriguingly, this inequality is the “inverse” of the isoperimetric inequality for a volume V in Euclidean (D-1) space bounded by a surface of area A, for which R≤1. Our conjectured reverse isoperimetric inequality can be interpreted as the statement that the entropy inside a horizon of a given ”volume” V is maximized for Schwarzschild-AdS. The thermodynamic definition of V requires a cosmological constant (or gauge coupling constant). However, except in seven dimensions, a smooth limit exists where Λ or g goes to zero, providing a definition of V even for asymptotically flat black holes.
  • Publication
    Hierarchies from D-brane Instantons in Globally Defined Calabi-Yau Orientifolds
    (2008-06-24) Cvetič, Mirjam; Weigand, Timo
    We construct the first globally consistent semirealistic type I string vacua on an elliptically fibered manifold where the zero modes of the Euclidean D1-instanton sector allow for the generation of nonperturbative Majorana masses of an intermediate scale. In another class of global models, a D1-brane instanton can generate a Polonyi-type superpotential breaking supersymmetry at an exponentially suppressed scale.
  • Publication
    Extremal Black Hole/CFT Correspondence in (Guaged) Supergravities
    (2009-04-10) Chow, David D.K.; Cvetič, Mirjam; Lü, H.; Pope, C. N.
    We extend the investigation of the recently proposed Kerr/conformal field theory correspondence to large classes of rotating black hole solutions in gauged and ungauged supergravities. The correspondence, proposed originally for four-dimensional Kerr black holes, asserts that the quantum states in the near-horizon region of an extremal rotating black hole are holographically dual to a two-dimensional chiral theory whose Virasoro algebra arises as an asymptotic symmetry of the near-horizon geometry. In fact, in dimension D there are [(D - 1)/2] commuting Virasoro algebras. We consider a general canonical class of near-horizon geometries in arbitrary dimension D, and show that in any such metric the [(D - 1)/2] central charges each imply, via the Cardy formula, a microscopic entropy that agrees with the Bekenstein- Hawking entropy of the associated extremal black hole. In the remainder of the paper we show for most of the known rotating black hole solutions of gauged supergravity, and for the ungauged supergravity solutions with four charges in D = 4 and three charges in D = 5, that their extremal near-horizon geometries indeed lie within the canonical form. This establishes that, in all these examples, the microscopic entropies of the dual conformal field theories agree with the Bekenstein-Hawking entropies of the extremal rotating black holes.
  • Publication
    Warped Resolved La,b,c Cones
    (2008-06-03) Cvetič, Mirjam; Vázquez-Poritz, J. F.
    We construct supergravity solutions describing a stack of D3-branes localized at a point on a blown-up cycle of a resolved La,b,c cone. The geometry flows from AdS5 × La,b,c to AdS5 × S5 × Zk. The corresponding quiver gauge theory undergoes a renormalization group flow between two superconformal fixed points, which leads to semi-infinite chains of flows between the various La;b;c fixed points. The general system is described by a triplet of Heun equations, which can each be solved by an expansion with a three-term recursion relation, though there are closed-form solutions for certain cases. This enables us to read off the operators that acquire nonzero vacuum expectation values as the quiver gauge theory flows away from a fixed point.
  • Publication
    Gravity Trapping on a Finite Thickness Domain Wall: An Analytic Study
    (2008-06-03) Cvetič, Mirjam; Robnik, Marko
    We construct an explicit model of the gravity trapping domain-wall potential, where for the first time we can study explicitly the graviton wave function fluctuations for any thickness of domain wall. A concrete form of the potential depends on one parameter 0 ≤ x ≤ π/2 , which effectively parameterizes the thickness of the domain wall with specific limits x → 0 and x → π/2 2 corresponding to the thin and the thick wall, respectively. The analysis of continuum Kaluza-Klein fluctuations yields explicit expressions for both small and large Kaluza-Klein energy. We also derive specific explicit conditions in the regime x > 1, for which the fluctuation modes exhibit a resonance behavior, and which could sizably affect the modifications of the four-dimensional Newton’s law at distances that typically are by 4 orders of magnitude larger than those relevant for Newton’s law modifications of thin walls.
  • Publication
    Universal Area Product Formulas for Rotating and Charged Black Holes in Four and Higher Dimensions
    (2011-03-21) Cvetič, Mirjam; Gibbons, Gary W.; Pope, Christopher N.
    We present explicit results for the product of all horizon areas for general rotating multicharge black holes, both in asymptotically flat and asymptotically anti–de Sitter spacetimes in four and higher dimensions. The expressions are universal, and depend only on the quantized charges, quantized angular momenta and the cosmological constant. If the latter is also quantized these universal results may provide a ‘‘looking glass’’ for probing the microscopics of general black holes.