non-BPS D-branes Research Articles

Non-BPS fractional branes with Bose-Fermi cancellation in asymmetric orbifolds

We study non-BPS D-branes in the type II string vacua with chiral space-time SUSY constructed based on the asymmetric orbifolds of mathrm{K}3cong {T}^4/{mathrm{mathbb{Z}}}_2 as a succeeding work of [21]. We especially focus on the fractional D-branes that contains the contributions from the twisted sector of the {mathrm{mathbb{Z}}}_2 -orbifolding.We show that the cylinder partition functions for these fractional branes do not vanish, as in the cases of ordinary non-BPS D-branes. This aspect is in a sharp contrast with the bulk-type branes studied in [21]. We then discuss the extensions of models by including the discrete torsion depending on the spin structures, and investigate whether we obtain the vanishing self-overlaps associated to the fractional branes. The existence/absence of bose-fermi cancellations both in the closed and open string spectra as well as the massless spectra in the twisted sectors crucially depend on the discrete torsion. We find that some choices of the torsion indeed realize the vanishing self-overlaps for the fractional branes, with keeping the vanishing torus partition function intact.

Spherical D-brane by tachyon condensation

We find a novel tachyon condensation which provides a D-brane system with spherical worldvolume in the flat spacetime. The tachyon profile is a deformation of a known D0-brane solution on non-BPS D3-branes in type IIA superstring theory, which realizes a bound state of a spherical D2-brane and a D0-brane. The D0-brane is resolved into the sphere as a $U(1)$ monopole flux of the unit magnetic charge. We show that the system has the correct tension and the RR-coupling. Although the low energy effective action of the system is the same as that of the dual description of the fuzzy sphere solution of multiple D0-branes, our system cannot be equivalent to the fuzzy sphere. We argue that the sphere can be stable in a certain RR-flux background. The use of projective modules in describing the tachyon condensation is emphasized.

Non-supersymmetric D-branes with vanishing cylinder amplitudes in asymmetric orbifolds

We study the type II string vacua with chiral space-time SUSY constructed as asymmetric orbifolds of torus and K3 compactifications. Despite the fact that all the D-branes are non-BPS in any chiral SUSY vacua, we show that the relevant non-geometric vacua of asymmetric orbifolds allow rather generally configurations of D-branes which lead to vanishing cylinder amplitudes, implying the bose-fermi cancellation at each mass level of the open string spectrum. After working on simple models of toroidal asymmetric orbifolds, we focus on the asymmetric orbifolds of T2 × ℳ, where ℳ is described by a general mathcal{N} = 4 SCFT with c = 6 defined by the Gepner construction for K3. Even when the modular invariant partition functions in the bulk remain unchanged, the spectra of such non-BPS D-branes with the bose-fermi cancellation can vary significantly according to the choice of orbifolding.

Analytic solution for tachyon condensation in Berkovits’ open superstring field theory

We present an analytic solution for tachyon condensation on a non-BPS D-brane in Berkovits' open superstring field theory. The solution is presented as a product of $2\times 2$ matrices in two distinct $GL_2$ subgroups of the open string star algebra. All string fields needed for computation of the nonpolynomial action can be derived in closed form, and the action produces the expected non-BPS D-brane tension in accordance with Sen's conjecture. We also comment on how D-brane charges may be encoded in the topology of the tachyon vacuum gauge orbit.

Electromagnetic and thermal responses in topological matter: Topological terms, quantum anomalies and D-branes

We discuss the thermal (or gravitational) responses in topological superconductors and in topological phases in general. Such thermal responses (as well as electromagnetic responses for conserved charge) provide a definition of topological insulators and superconductors beyond the single-particle picture. In two-dimensional topological phases, the Str\v{e}da formula for the electric Hall conductivity is generalized to the thermal Hall conductivity. Applying this formula to the Majorana surface states of three-dimensional topological superconductors predicts cross-correlated responses between the angular momentum and thermal polarization (entropy polarization). We also discuss a use of D-branes in string theory as a systematic tool to derive all such topological terms and topological responses. In particular, we relate the $\mathbb{Z}_2$ index of topological insulators introduced by Kane and Mele (and its generalization to other symmetry classes and to arbitrary dimensions) to the K-theory charge of non-BPS D-branes, and vice versa. We thus establish a link between the stability of non-BPS D-branes and the topological stability of topological insulators.

Exotic universal solutions in cubic superstring field theory

We present a class of analytic solutions of cubic superstring field theory in the universal sector on a non-BPS D-brane. Computation of the action and gauge invariant overlap reveal that the solutions carry half the tension of a non-BPS D-brane. However, the solutions do not satisfy the reality condition. In fact, they display an intriguing topological structure: We find evidence that conjugation of the solutions is equivalent to a gauge transformation that cannot be continuously deformed to the identity.

Dirac-Born-Infeld actions and tachyon monopoles

We investigate magnetic monopole solutions of the non-abelian DBI action describing 2 coincident non-BPS D9-branes in flat space. Just as in the case of kink and vortex solitonic tachyon solutions of the full DBI non-BPS actions, as previously analyzed by Sen, these monopole configurations are singular in the first instance and require regularization. We discuss a suitable non-abelian ansatz and show it solves the equations of motion to leading order in the regularization parameter. Fluctuations are studied and shown to describe a codimension 3 BPS D6-brane. A formula is derived for its tension. We comment on the implication to our results from both the trace (Tr) and symmetrized trace (Str) prescriptions of the non-abelian DBI action of coincident non-BPS D9-branes.

Bouncing universe and non-BPS branes

We describe string frame bouncing universe scenarios involving the creation and annihilation of a non-BPS D9-brane in type IIA superstring theory. We find several classes of solutions, in which the bounce is driven by the tachyon dynamics of the non-BPS brane. The metric and dilaton during the bounce are consistently described in terms of the lowest order effective action. The bounce solutions interpolate between contracting and expanding pre-big bang (or post-big bang) solutions. The singular behavior of our bounce solutions is the same as that of the pre-big bang (or post-big bang) solution.

Creation of Non-BPS D9-branes from Hagedorn Transition of Closed Strings

Creation of Non-BPS D9-branes from Hagedorn Transition of Closed Strings

Non Abelian tachyon kinks

Starting from the action of two coincident non-BPS D9-branes, we investigate kink configurations of the U(2) matrix tachyon field. We consider both Str and Tr prescriptions for the trace over gauge indices of the non-BPS action. Non-abelian tachyon condensation in the theory with Tr prescription, and the resulting fluctuations about the kink profile, are shown to give rise to a theory of two coincident BPS D8-branes. This is a natural non-abelian generalization of Sen's mechanism of tachyon condensation on a single non-BPS Dp-brane yielding a single BPS brane of codimesion one. By contrast, starting with the Str gauge trace prescription of the coincident non-BPS D9-brane action, such a generalization of Sen's mechanism appears problematic.

Tachyon solution in a cubic Neveu-Schwarz string field theory

We find a class of analytic solutions in a modified cubic theory of fermionic strings that includes the GSO(−) sector. This class contains a solution that involves a tachyon field from the GSO(−) sector and reproduces the correct value of the non-BPS D-brane tension.

On the classical equivalence of superstring field theories

We construct mappings that send solutions of the cubic and non-polynomial open superstring field theories to each other. We prove that the action is invariant under the maps and that gauge orbits are mapped into gauge orbits. It follows that the perturbative spectrum around solutions is the same in both theories. The mappings also preserve the string field reality condition. We generalize to the cases of a non-BPS D-brane and of multi-D-brane systems. We analyze the recently found analytical solutions of the cubic action, both in the BPS sector and the non-BPS sector and show that they span a one parameter family of solutions with empty cohomology and identical action, which suggests that they are gauge equivalent. We write the gauge transformations relating these solutions explicitly. This seems to suggest that open superstring field theory is able to describe a vacuum solution even around a BPS D-brane.

On higher derivative corrections of tachyon action

We have examined the momentum expansion of the disk level S-matrix element of two tachyons and two gauge fields to find, up to on-shell ambiguity, the couplings of these fields in the world volume theory of N coincident non-BPS D-branes to all order of α ′ . Using the proposal that the action of D-brane–anti-D-brane is given by the projection of the action of two non-BPS D-branes with ( − 1 ) F L , we find the corresponding couplings in the world volume theory of the brane–anti-brane system. Using these infinite tower of couplings, we then calculate the massless pole of the scattering amplitude of one RR field, two tachyons and one gauge field in the brane–anti-brane theory. We find that the massless pole of the field theory amplitude is exactly equal to the massless pole of the disk level S-matrix element of one RR, two tachyons and one gauge field to all order of α ′ . We have also found the couplings of four tachyons to all order of α ′ by examining the S-matrix element of four tachyons.

Inflation conditions for non-BPS D-branes

We investigate the effective action for a non-BPS brane in a time-dependent embedding. This action is considered as the action for tachyon and embedding coupled to the brane gravity. We derive the slow-roll parameters from this model.

Non-BPS D9-Branes in the Early Universe

We have investigated the finite temperature systems of non-BPS D-branes and D-brane-anti-D-brane pairs in the previous papers. It has been shown that non-BPS D9-branes and D9-anti-D9 pairs become stable near the Hagedorn temperature on the basis of boundary string field theory. This implies that there is a possibility that these spacetime-filling branes exist in the early universe. We study the time evolution of the universe in the presence of non-BPS D9-branes on the basis of boundary string field theory in this paper. We try to construct the following scenario for the early universe: The universe expands at high temperature and the open string gas on the non-BPS D9-branes dominates the total energy of the system at first. The temperature decreases as the universe expands. Then the non-BPS D9-branes become unstable at low temperature and decay through tachyon condensation. We obtain some classical solutions for Einstein gravity and dilaton gravity in the very simple cases.

Non-BPS D9-branes in the Early Universe(Fundamental Problems and Applications of Quantum Field Theory-Topological Aspects of Quantum Field Theory-)

Non-BPS D9-branes in the Early Universe(Fundamental Problems and Applications of Quantum Field Theory-Topological Aspects of Quantum Field Theory-)

DDF construction and D-brane boundary states in pure spinor formalism

Open string boundary conditions for non-BPS D-branes in type II string theories discussed in hep-th/0505157 give rise to two sectors with integer (R sector) and half-integer (NS sector) modes for the combined fermionic matter and bosonic ghost variables in pure spinor formalism. Exploiting the manifest supersymmetry of the formalism we explicitly construct the DDF (Del Giudice, Di Vecchia, Fubini) states in both the sectors which are in one-to-one correspondence with the states in light-cone Green-Schwarz formalism. We also give a proof of validity of this construction. A similar construction in the closed string sector enables us to define a physical Hilbert space in pure spinor formalism which is used to project the covariant boundary states of both the BPS and non-BPS instantonic D-branes. These projected boundary states take exactly the same form as those found in light-cone Green-Schwarz formalism and are suitable for computing the cylinder diagram with manifest open-closed duality.

D-brane spectrum and K-theory constraints ofD= 4, Script N = 1 orientifolds

We study the spectrum of stable BPS and non-BPS D-branes in Z_2 x Z_2 orientifolds for all choices of discrete torsion between the orbifold and orientifold generators. We compute the torsion K-theory charges in these D=4, N=1 orientifold models directly from worldsheet conformal field theory, and compare with the K-theory constraints obtained indirectly using D-brane probes. The K-theory torsion charges derived here provide non-trivial constraints on string model building. We also discuss regions of stability for non-BPS D-branes in these examples.

Fundamental strings and NS5-branes from unstable D-branes in supergravity

By using the non-supersymmetric p -brane solutions delocalized in arbitrary number of transverse directions in type II supergravities, we show how they can be regarded as interpolating solutions between unstable D p -branes (a non-BPS D-brane or a pair of coincident D-brane–anti-D-brane) and fundamental strings and also between unstable D p -branes and NS5-branes. We also show that some of these solutions can be regarded as interpolating solutions between NS5/ NS ¯ 5 and D p -branes (for p ⩽ 5 ). This gives a closed string description of the tachyon condensation and lends support to the conjecture that the open string theory on unstable D-branes at the tachyonic vacuum has soliton solutions describing not only the lower-dimensional BPS D-branes, but also the fundamental strings as well as the NS5-branes.

Non-BPS D9-branes in the early universe

We have investigated the finite temperature systems of non-BPS D-branes and D-brane?anti-D-brane pairs in the previous papers. It has been shown that non-BPS D9-branes and D9- pairs become stable near the Hagedorn temperature on the basis of boundary string field theory. This implies that there is a possibility that these spacetime-filling branes exist in the early universe. We study the time evolution of the universe in the presence of non-BPS D9-branes on the basis of boundary string field theory in this paper. We try to construct the following scenario for the early universe: The universe expands at high temperature and the open string gas on the non-BPS D9-branes dominates the total energy of the system at first. The temperature decreases as the universe expands. Then the non-BPS D9-branes become unstable at low temperature and decay through tachyon condensation. We obtain some classical solutions for Einstein gravity and dilaton gravity in the very simple cases.