arXiv subjects

Donam Youm

Publications and source records attributed to Donam Youm.

At least 37 records · Page 2Linked to original sources

arXiv2001

Cosmology of Dilatonic Brane World

We study cosmological solutions in the dilatonic brane world models. The effective four-dimensional equations on the brane are analyzed for the models with one positive tension brane and two branes with tensions of opposite signs. Just as in the non-dilatonic brane case, the conventional Friedmann equations of the four-dimensional universe are reproduced to the leading order in matter energy density for the model with one brane and the introduction of a radion potential is required in order to reproduce the Friedmann equations with the correct sign for the model with two branes.

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arXiv2000

BPS Solitons in M5-Brane Worldvolume Theory with Constant Three-Form Field

We study BPS solutions for a self-dual string and a neutral string in M5-brane worldvolume theory with constant three-form field. We further generalize such solitons to superpose with a calibrated surface. We also study a traveling wave on a calibrated surface in the constant three-form field background.

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arXiv2000

Bulk Fields in Dilatonic and Self-Tuning Flat Domain Walls

We study the Kaluza-Klein zero modes of massless bulk fields with various spins in the background of dilatonic and self-tuning flat domain walls. We find that the zero modes of all the massless bulk fields in such domain wall backgrounds are normalizable, unlike those in the background of the non-dilatonic domain wall with infinite extra space of Randall and Sundrum. In particular, gravity in the bulk of dilatonic domain walls is effectively compactified to the Einstein gravity with vanishing cosmological constant and nonzero gravitational constant in one lower dimensions for any values of dilaton coupling parameter, provided the warp factor is chosen to decrease on both sides of the domain wall, in which case the tension of the domain wall is positive. However, unexpectedly, for the self-tuning flat domain walls, the cosmological constant of the zero mode effective gravity action in one lower dimensions does not vanish, indicating the need for additional ingredient or modification necessary in cancellation of the unexpected cosmological constant in the graviton zero mode effective action.

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arXiv2000

q-Deformed Conformal Quantum Mechanics

We construct a q-deformed version of the conformal quantum mechanics model of de Alfaro, Fubini and Furlan for which the deformation parameter is complex and the unitary time evolution of the system is preserved. We also study differential calculus on the q-deformed quantum phase space associated with such system.

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arXiv2000

Localization of Gravity on Dilatonic Domain Walls: Addendum to ``Solitons in Brane Worlds''

We supplement the discussion on localization of gravity on dilatonic domain walls in ``Solitons in Brane Worlds'' (Nucl. Phys. B576, 106, hep-th/9911218) by giving unified and coherent discussion which combines the result of this paper and the expanded results in the author's subsequent papers in an attempt to avoid misleading readers. We also discuss the possible string theory embeddings of the Randall-Sundrum type brane world scenarios through non-dilatonic and dilatonic domain walls, which straightforwardly follows from the author's previous works but was not elaborated explicitly.

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arXiv2000

Extra Force in Brane Worlds

By carefully analyzing the geodesic motion of a test particle in the bulk of brane worlds, we identify an extra force which is recognized in spacetime of one lower dimensions as a non-gravitational force acting on the particle. Such extra force acts on the particle in such a way that the conventional particle mechanics in one lower dimensions is violated, thereby hinting at the higher-dimensional origin of embedded spacetime in the brane world scenario. We obtain the explicit equations describing the motion of the bulk test particle as observed in one lower dimensions for general gravitating configurations in brane worlds and identify the extra non-gravitational force acting on the particle measured in one lower dimensions.

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arXiv2000

A Note on (D(p-2),Dp) Bound State and Noncommutative Yang-Mills Theory

We give a microscopic explanation for the recently observed equivalence among thermodynamics of supergravity solutions for Dp-branes with or without NS B-field and for D(p-2)-branes with vanishing B-field and two delocalized transverse directions by showing that these D-brane configurations are related to one another through T-duality transformations. This result also gives an evidence for the equivalence among the noncommutative and the ordinary Yang-Mills theories corresponding to the decoupling limits of the worldvolume theories of such D-brane configurations.

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arXiv2000

Solitons in Brane Worlds

We study some aspects of dilatonic domain walls in relation to the idea on the noncompact internal space. We find that the warp factor in the spacetime metric increases as one moves away from the domain wall for all the supersymmetric dilatonic domain wall solutions obtained from the (intersecting) BPS branes in string theories through toroidal compactifications, unlike the case of the Randall-Sundrum model. On the other hand, when the dilaton coupling parameter a for the D-dimensional extreme dilatonic domain wall takes the values |a|<2/(D-2), the Kaluza-Klein spectrum of graviton has the same structure as that of the Randall-Sundrum model (and the warp factor decreases in the finite interval around the dilatonic domain wall), thereby implying the possibility of extending the Randall-Sundrum model to the |a|<2/(D-2) case. We construct fully localized solutions describing extreme dilatonic branes within extreme dilatonic domain walls and the supersymmetric branes within the supersymmetric domain walls of string theories. These solutions are valid in any region of spacetime, not just in the region close to the domain walls.

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arXiv2000

Dilatonic p-Branes and Brane Worlds

We study a general dilatonic p-brane solution in arbitrary dimensions in relation to the Randall-Sundrum scenario. When the p-brane is fully localized along its transverse directions, the Kaluza-Klein zero mode of bulk graviton is not normalizable. When the p-brane is delocalized along its transverse directions except one, the Kaluza-Klein zero mode of bulk graviton is normalizable if the warp factor is chosen to increase, in which case there are singularities at finite distance away from the p-brane. Such delocalized p-brane can be regarded as a dilatonic domain wall as seen in higher dimensions. This unusual property of the warp factor allows one to avoid a problem of dilatonic domain wall with decreasing warp factor that free massive particles are repelled from the domain wall and hit singularities, since massive particles with finite energy are trapped around delocalized p-branes with increasing warp factor by gravitational force and can never reach the singularities.

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arXiv2000

Probing Solitons in Brane Worlds

We study dynamics of a probe p-brane and a test particle in the field background of fully localized solutions describing the source p-brane within the worldvolume of the source domain wall. We find that the probe dynamics in the background of the source p-brane in one lower dimensions is not reproduced, indicating that p-branes within the worldvolume of domain walls perhaps describe an exotic phase of p-branes in brane worlds. We speculate therefore that a (p+1)-brane where one of its longitudinal directions is along the direction transverse to the domain wall is the right description of the p-brane in the brane world with the expected properties.

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arXiv2000

Solitons in Brane Worlds II

We study the solution describing a non-extreme dilatonic (p+1)-brane intersecting a D-dimensional extreme dilatonic domain wall, where one of its longitudinal directions is along the direction transverse to the domain wall, in relation to the Randall-Sundrum type model. The dynamics of the probe (p+1)-brane in such source background reproduces that of the probe p-brane in the background of the (D-1)-dimensional source p-brane. However, as for a probe test particle, the dynamics in one lower dimensions is reproduced, only when the source (p+1)-brane is uncharged.

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arXiv2000

A Note on Solitons in Brane Worlds

We obtain the zero mode effective action for gravitating objects in the bulk of dilatonic domain walls. Without additional fields included in the bulk action, the zero mode effective action reproduces the action in one lower dimensions obtained through the ordinary Kaluza-Klein (KK) compactification, only when the transverse (to the domain wall) component of the bulk metric does not have non-trivial term depending on the domain wall worldvolume coordinates. With additional fields included in the bulk action, non-trivial dependence of the transverse metric component on the domain wall worldvolume coordinates appears to be essential in reproducing the lower-dimensional action obtained via the ordinary KK compactification. We find, in particular, that the effective action for the charged (p+1)-brane in the domain wall bulk reproduces the action for the p-brane in one lower dimensions.

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arXiv1999

(Generalized) Conformal Quantum Mechanics of 0-Branes and Two-Dimensional Dilaton Gravity

We study the relation between the (generalized) conformal quantum mechanics of 0-branes and the two-dimensional dilaton gravity. The two-dimensional actions obtained from the supergravity effective actions for the (dilatonic) 0-branes through the compactification on a sphere are related to known two-dimensional dilaton gravity models. The SL(2,R) symmetry of the (generalized) conformal quantum mechanics is realized within such two-dimensional models. The two-dimensional dilatonic gravity model derived from the non-dilatonic 0-brane action is related to the Liouville theory and therefore is conformal, whereas the two-dimensional model derived from the dilatonic 0-brane action does not have the conformal symmetry.

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arXiv1999

Black Hole Thermodynamics and Two-Dimensional Dilaton Gravity Theory

We relate various black hole solutions in the near-horizon region to black hole solutions in two-dimensional dilaton gravity theories in order to argue that thermodynamics of black holes in D>=4 can be effectively described by thermodynamics of black holes in two-dimensional dilaton gravity theories. We show that the Bekenstein-Hawking entropies of single-charged dilatonic black holes and dilatonic p-branes with an arbitrary dilaton coupling parameter in arbitrary spacetime dimensions are exactly reproduced by the Bekenstein-Hawking entropy of the two-dimensional black hole in the associated two-dimensional dilaton gravity model. We comment that thermodynamics of non-extreme stringy four-dimensional black hole with four charges and five-dimensional black hole with three charges may be effectively described by thermodynamics of the black hole solutions with constant dilaton field in two-dimensional dilaton gravity theories.

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arXiv1999

Probing partially localized supergravity background of fundamental string ending on Dp-brane

We study the dynamics of the probe fundamental string in the field background of the partially localized supergravity solution for the fundamental string ending on Dp-brane. We separately analyze the probe dynamics for its motion along the worldvolume direction and the transverse direction of the source Dp-brane. We compare the dynamics of the probe along the Dp-brane worldvolume direction to the BIon dynamics.

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arXiv1999

Delocalized Supergravity Solutions for Brane/Anti-brane Systems and their Bound States

We obtain various solutions for D=4 dipoles and their bound states whose U(1) fields originate from various form fields in the effective string theories. We oxidize such dipole solutions to D=10 to obtain delocalized supergravity solutions for the brane/anti-brane pairs and their bound states. We speculate on generalized harmonic superposition rules for supergravity solutions for (intersecting) brane/anti-brane pairs.

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arXiv1999

Supergravity Solutions for BI Dyons

We construct partially localized supergravity counterpart solutions to the 1/2 supersymmetric non-threshold and the 1/4 supersymmetric threshold bound state BI dyons in the D3-brane Dirac-Born-Infeld theory. Such supergravity solutions have all the parameters of the BI dyons. By applying the IIA/IIB T-duality transformations to these supergravity solutions, we obtain the supergravity counterpart solutions to 1/2 and 1/4 supersymmetric BIons carrying electric and magnetic charges of the worldvolume U(1) gauge field in the Dirac-Born-Infeld theory in other dimensions.

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arXiv1999

Partially Localized Intersecting BPS Branes

We present the explicit forms of supergravity solutions for the various intersecting two BPS branes in eleven and ten dimensions, where one brane is localized at the delocalized other brane. Our partially localized supergravity solutions describe brane configurations in the near horizon region of the delocalized branes, where the two constituent branes meet in the overall transverse space and the delocalized branes coincide. We also give the brane worldvolume interpretations for some of such supergravity solutions.

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