arXiv subjects

Jennie Traschen

Publications and source records attributed to Jennie Traschen.

At least 55 records · Page 3Linked to original sources

arXiv2003

Tension Perturbations of Black Brane Spacetimes

We consider black-brane spacetimes that have at least one spatial translation Killing field that is tangent to the brane. A new parameter, the tension of a spacetime, is defined. The tension parameter is associated with spatial translations in much the same way that the ADM mass is associated with the time translation Killing field. In this work, we explore the implications of the spatial translation symmetry for small perturbations around a background black brane. For static charged black branes we derive a law which relates the tension perturbation to the surface gravity times the change in the the horizon area, plus terms that involve variations in the charges and currents. We find that as a black brane evaporates the tension decreases. We also give a simple derivation of a first law for black brane spacetimes. These constructions hold when the background stress-energy is governed by a Hamiltonian, and the results include arbitrary perturbative stress-energy sources.

gr-qc↗

arXiv2003

A Positivity Theorem for Gravitational Tension in Brane Spacetimes

We study transverse asymptotically flat spacetimes without horizons that arise from brane matter sources. We assume that asymptotically there is a spatial translation Killing vector that is tangent to the brane. Such spacetimes are characterized by a tension, analogous to the ADM mass, which is a gravitational charge associated with the asymptotic spatial translation Killing vector. Using spinor techniques, we prove that the purely gravitational contribution to the spacetime tension is positive definite.

hep-th↗

arXiv2002

A Positive Energy Theorem for Asymptotically deSitter Spacetimes

We construct a set of conserved charges for asymptotically deSitter spacetimes that correspond to asymptotic conformal isometries. The charges are given by boundary integrals at spatial infinity in the flat cosmological slicing of deSitter. Using a spinor construction, we show that the charge associated with conformal time translations is necessarilly positive and hence may provide a useful definition of energy for these spacetimes. A similar spinor construction shows that the charge associated with the time translation Killing vector of deSitter in static coordinates has both positive and negative definite contributions. For Schwarzshild-deSitter the conformal energy we define is given by the mass parameter times the cosmological scale factor. The time dependence of the charge is a consequence of a non-zero flux of the corresponding conserved current at spatial infinity. For small perturbations of deSitter, the charge is given by the total comoving mass density.

hep-th↗

arXiv2000

An Introduction to Black Hole Evaporation

Classical black holes are defined by the property that things can go in, but don't come out. However, Stephen Hawking calculated that black holes actually radiate quantum mechanical particles. The two important ingredients that result in back hole evaporation are (1) the spacetime geometry, in particular the black hole horizon, and (2) the fact that the notion of a "particle" is not an invariant concept in quantum field theory. These notes contain a step-by-step presentation of Hawking's calculation. We review portions of quantum field theory in curved spacetime and basic results about static black hole geometries, so that the discussion is self-contained. Calculations are presented for quantum particle production for an accelerated observer in flat spacetime, a black hole which forms from gravitational collapse, an eternal Schwarzschild black hole, and charged black holes in asymptotically deSitter spacetimes. The presentation highlights the similarities in all these calculations. Hawking radiation from black holes also points to a profound connection between black hole dynamics and classical thermodynamics. A theory of quantum gravity must predicting and explain black hole thermodynamics. We briefly discuss these issues and point out a connection between black hole evaportaion and the positive mass theorems in general relativity.

gr-qc↗

arXiv2000

Calibrations and Fayyazuddin-Smith Spacetimes

We show that a class of spacetimes introduced by Fayyazuddin and Smith to describe intersecting M5-branes admit a generalized Kahler calibration. Equipped with this understanding, we are able to construct spacetimes corresponding to further classes of calibrated $p$-brane world-volume solitons. We note that these classes of spacetimes also describe the fields of $p$-branes wrapping certain supersymmetric cycles of Calabi-Yau manifolds.

hep-th↗

arXiv2000

The Dynamics of Collapsing Monopoles and Regular Black Holes

We study the formation and stability of regular black holes by employing a thin shell approximation to the dynamics of collapsing magnetic monopoles. The core deSitter region of the monopole is matched across the shell to a Reissner-Nordstrom exterior. We find static configurations which are nonsingular black holes and also oscillatory trajectories about these static points that share the same causal structure. In these spacetimes the shell is always hidden behind the black hole horizon. We also find shell trajectories that pass through the asymptotically flat region and model collapse of a monopole to form a regular black hole. In addition there are trajectories in which the deSitter core encompasses a deSitter horizon and hence undergoes topological inflation. However, these always yield singular black holes and never have the shell passing through the aymptotically flat region. Although the regular black hole spacetimes satisfy the strong energy condition, they avoid the singularity theorems by failing to satisfy the genericity condition on the Riemann tensor. The regular black holes undergo a change in spatial topology in accordance with a theorem of Borde's.

hep-th↗

arXiv1999

Fully Localized Brane Intersections - The Plot Thickens

We study fully localized BPS brane solutions in classical supergravity using a perturbative approach to the coupled Born-Infeld/bulk supergravity system. We derive first order bulk supergravity fields for world-volume solitons corresponding to intersecting M2-branes and to a fundamental string ending on a D3-brane. One interesting feature is the appearance of certain off-diagonal metric components and corresponding components of the gauge potentials. Making use of a supersymmetric ansatz for the exact fields, we formulate a perturbative expansion which applies to $M2 \perp M2 (0), M5 \perp M5 (3)$ and $Dp \perp Dp (p-2)$ intersections. We find that perturbation theory qualitatively distinguishes between certain of these cases: perturbation theory breaks down at second order for intersecting M2-branes and D$p$-branes with $p\le 3$ while it is well behaved, at least to this order, for the remaining cases. This indicates that the behavior of the full non-linear intersecting Dp-brane solutions may be qualitatively different for $p \le 3$ than for $p \ge 4$, and that fully localized asymptotically flat solutions for $p \le 3$ may not exist. We discuss the consistency of these results with world-volume field theory properties.

hep-th↗

arXiv1999

Dynamics of the DBI Spike Soliton

We compare oscillations of a fundamental string ending on a D3-brane in two different settings: (1) a test-string radially threading the horizon of an extremal black D3-brane and (2) the spike soliton of the DBI effective action for a D3-brane. Previous work has shown that overall transverse modes of the test-string appear as l=0 modes of the transverse scalar fields of the DBI system. We identify DBI world-volume degrees of freedom that have dynamics matching those of the test-string relative transverse modes. We show that there is a map, resembling T-duality, between relative and overall transverse modes for the test-string that interchanges Neumann and Dirichlet boundary conditions and implies equality of the absorption coefficients for both modes. We give general solutions to the overall and relative transverse parts of the DBI coupled gauge and scalar system and calculate absorption coefficients for the higher angular momentum modes in the low frequency limit. We find that there is a nonzero amplitude for l>0 modes to travel out to infinity along the spike, demonstrating that the spike remains effectively 3+1-dimensional.

hep-th↗

arXiv1998

BPS Force Balances via Spin-Spin Interactions

We study two systems of BPS solitons in which spin-spin interactions are important in establishing the force balances which allow static, multi-soliton solutions to exist. Solitons in the Israel-Wilson-Perjes (IWP) spacetimes each carry arbitrary, classical angular momenta. Solitons in the Aichelburg-Embacher "superpartner" spacetimes carry quantum mechanical spin, which originates in the zero-modes of the gravitino field of N=2 supergravity in an extreme Reissner-Nordstrom background. In each case we find a cancellation between gravitational spin-spin and magnetic dipole-dipole forces, in addition to the usual one between Newtonian gravitational attraction and Coulombic electrostatic repulsion. In both cases, we analyze the forces between two solitons by treating one of the solitons as a probe or test particle, with the appropriate properties, moving in the background of the other. In the IWP case, the equation of motion for a spinning test particle, originally due to Papapetrou, includes a coupling between the background curvature and the spin of the test particle. In the superpartner case, the relevant equation of motion follows from a kappa-symmetric superparticle action.

hep-th↗

arXiv1998

The Spin of the M2-Brane and Spin-Spin Interactions via Probe Techniques

The 256 dimensional M2-brane multiplet contains solitons of many different intrinsic spins. Using the broken supersymmetry transformations of the M2-brane, we find supergravity solutions which explicitly display these spins. This amounts to quantizing the fermionic zero modes and computing the back reaction on the metric and gauge potential. These spacetime fields are therefore operator valued and acquire a conventional classical meaning only after taking expectations in given BPS states. Our spinning spacetimes are not of the standard Kerr form -- there is a non-vanishing gravitino. Nevertheless, the solutions have angular momentum and magnetic dipole moments with a g-factor of 2. We use probe techniques to study scattering of spinning BPS M2-branes. The static interactions cancel between like-sign branes at leading order, but there are static spin-spin forces between branes and anti-branes. The general probe-background Lagrangian contains gravitational spin-spin and magnetic dipole-dipole forces, as well as gravitino exchanges which allow branes to change fermion number.

hep-th↗

arXiv1997

A Very Effective String Model?

Additional evidence is presented for a recently proposed effective string model, conjectured to hold throughout the parameter space of the basic 5 dimensional, triply charged black holes, which includes the effects of brane excitations, as well as momentum modes. We compute the low energy spacetime absorption coefficient $σ$ for the scattering of a triply-charged scalar field in the near extremal case, and conjecture an exact form for $σ$. It is shown that this form of $σ$ arises simply from the effective string model. This agreement encompasses both statistical factors coming from the Bose distributions of string excitations and a prefactor which depends on the effective string radius. An interesting feature of the effective string model is that the change in mass of the effective string system in an emission process is not equal to the change in the energies of the effective string excitations. If the model is valid, this may hold clues towards understanding back reaction due to Hawking radiation. A number of weak spots and open questions regarding the model are also noted.

hep-th↗

arXiv1997

U-Duality, D-Branes and Black Hole Emission Rates: Agreements and Disagreements

An expression for the spacetime absorption coefficient of a scalar field in a five dimensional, near extremal black hole background is derived, which has the same form as that presented by Maldacena and Strominger, but is valid over a larger, U-duality invariant region of parameter space and in general disagrees with the corresponding D-brane result. We develop an argument, based on D-brane thermodynamics, which specifies the range of parameters over which agreement should be expected. For neutral emission, the spacetime and D-brane results agree over this range. However, for charged emission, we find disagreement in the `Fat Black Hole' regime, in which charge is quantized in smaller units on the brane, than in the bulk of spacetime. We indicate a possible problem with the D-brane model in this regime. We also use the Born approximation to study the high frequency limit of the absorption coefficient and find that it approaches unity, for large black hole backgrounds, at frequencies still below the string scale, again in disagreement with D-brane results.

hep-th↗

arXiv1997

Instanton Supported Scalar Hair on Black Holes

We present analytical perturbative, and numerical solutions of the Einstein equation which describe a black hole with a nontrivial dilaton field and a purely topological gauge potential. The gauge potential has zero field strength and hence no stress-energy, but it does couple to virtual string worldsheets which wrap around the Euclidean horizon two-sphere, and generate an effective interaction in the spacetime lagrangian. We use the lagrangian with a nonstandard potential for a scalar field that reproduces the effect of the worldsheet instantons. As has been previously pointed out the topological charge Q of the gauge field can be detected by an Anharonov-Bohm type experiment using quantum strings; the classical scalar hair of the solutions here is a classical detection of Q. ADM mass, dilaton charge and Hawking temperature are calculated and compared with the known cases when appropriate. We discuss why these solutions do not violate the no-hair theorems and show that, for sufficiently small interaction coupling, the solutions are stable under linear time dependent perturbations.

gr-qc↗

arXiv1996

Overlapping Branes in M-Theory

We construct new supersymmetric solutions of $D$=11 supergravity describing $n$ orthogonally ``overlapping" membranes and fivebranes for $n$=2,\dots,8. Overlapping branes arise after separating intersecting branes in a direction transverse to all of the branes. The solutions, which generalize known intersecting brane solutions, preserve at least $2^{-n}$ of the supersymmetry. Each pairwise overlap involves a membrane overlapping a membrane in a 0-brane, a fivebrane overlapping a fivebrane in a 3-brane or a membrane overlapping a fivebrane in a string. After reducing $n$ overlapping membranes to obtain $n$ overlapping $D$-2-branes in $D$=10, $T$-duality generates new overlapping $D$-brane solutions in type IIA and type IIB string theory. Uplifting certain type IIA solutions leads to the $D$=11 solutions. Some of the new solutions reduce to dilaton black holes in $D$=4. Additionally, we present a $D$=10 solution that describes two $D$-5-branes overlapping in a string. $T$-duality then generates further $D$=10 solutions and uplifting one of the type IIA solutions gives a new $D$=11 solution describing two fivebranes overlapping in a string.

hep-th↗

arXiv1995

Breaking Cosmic Strings without Monopoles

It is shown that topologically stable cosmic strings can, in fact, appear to end or to break, even in theories without monopoles. This can occur whenever the spatial topology of the universe is nontrivial. For the case of Abelian-Higgs strings, we describe the gauge and scalar field configurations necessary for a string to end on a black hole. We give a lower bound for the rate at which a cosmic string will break via black hole pair production, using an instanton calculation based on the Euclidean C-metric.

gr-qc↗

arXiv1994

Discrete Self-Similiarity and Critical Point Behavior in Fluctuations About Extremal Black Holes

The issues of scaling symmetry and critical point behavior are studied for fluctuations about extremal charged black holes. We consider the scattering and capture of the spherically symmetric mode of a charged, massive test field on the background spacetime of a black hole with charge $Q$ and mass $M$. The spacetime geometry near the horizon of a $|Q|=M$ black hole has a scaling symmetry, which is absent if $|Q|<M$, a scale being introduced by the surface gravity. We show that this symmetry leads to the existence of a self-similiar solution for the charged field near the horizon, and further, that there is a one parameter family of discretely self-similiar solutions . The scaling symmetry, or lack thereof, also shows up in correlation length scales, defined in terms of the rate at which the influence of an external source coupled to the field dies off. It is shown by constructing the Greens functions, that an external source has a long range influence on the extremal background, compared to a correlation length scale which falls off exponentially fast in the $|Q|<M$ case. Finally it is shown that in the limit of $Δ\equiv (1-{Q^2 \overM^2} )^{1\over 2} \rightarrow 0$ in the background spacetime, that infinitesimal changes in the black hole area vary like $Δ^{1\over 2}$.

gr-qc↗

arXiv1993

Pair Creation of Dilaton Black Holes

We consider dilaton gravity theories in four spacetime dimensions parametrised by a constant $a$, which controls the dilaton coupling, and construct new exact solutions. We first generalise the C-metric of Einstein-Maxwell theory ($a=0$) to solutions corresponding to oppositely charged dilaton black holes undergoing uniform acceleration for general $a$. We next develop a solution generating technique which allows us to ``embed" the dilaton C-metrics in magnetic dilaton Melvin backgrounds, thus generalising the Ernst metric of Einstein-Maxwell theory. By adjusting the parameters appropriately, it is possible to eliminate the nodal singularities of the dilaton C-metrics. For $a<1$ (but not for $a\ge 1$), it is possible to further restrict the parameters so that the dilaton Ernst solutions have a smooth euclidean section with topology $S^2\times S^2-{\rm\{pt\}}$, corresponding to instantons describing the pair production of dilaton black holes in a magnetic field. A different restriction on the parameters leads to smooth instantons for all values of $a$ with topology $S^2\times \R^2$.

hep-th↗

arXiv1993

Particle Production and Positive Energy Theorems for Charged Black Holes in deSitter

We study quantum mechanical and classical stability properties of Reissner-Nordstrom deSitter spacetimes, which describe black holes with mass $M$ and charge $Q$ in a background with cosmological constant $Λ\ge 0$. There are two sources of particle production in these spacetimes; the black hole horizon and the cosmological horizon. A scattering calculation is done to compute the Hawking radiation in these spacetimes. We find that the flux from the black hole horizon equals the flux from the cosmological horizon, if and only if $|Q|=M$, indicating that this is a state of thermodynamic equilibrium. The spectrum, however, is not thermal. We also show that spacetimes containing a number of charge equal to mass black holes with $Λ\ge 0$, have supercovariantly constant spinors, suggesting that they may be minimum energy states in a positive energy construction. As a first step in this direction, we present a positive energy construction for asymptotically deSitter spacetimes with vanishing charge. Because the construction depends only on a spatial slice, our result also holds for spacetimes which are asymptotically Robertson-Walker.

gr-qc↗