3,341 research outputs found
Winding effects on brane/anti-brane pairs
We study a brane/anti-brane configuration which is separated along a compact
direction by constructing a tachyon effective action which takes into account
transverse scalars. Such an action is relevant in the study of HQCD model of
Sakai and Sugimoto of chiral symmetry breaking, where the size of the compact
circle sets the confinement scale. Our approach is motivated by string theory
orbifold constructions and gives a route to model inhomogeneous tachyon decay.
We illustrate the techniques involved with a relatively simple example of a
harmonic oscillator on a circle. We will then repeat the analysis for the
Sakai-Sugimoto model and show that by integrating out the winding modes will
provide us with a renormalized action with a lower energy than that of
truncating to zero winding sector.Comment: 21 pages, 3 figures. v3: discussion and references added, published
versio
Perturbation Theory for Singular Potentials in Quantum Mechanics
We study perturbation theory in certain quantum mechanics problems in which
the perturbing potential diverges at some points, even though the energy
eigenvalues are smooth functions of the coefficient of the potential. We
discuss some of the unusual techniques which are required to obtain
perturbative expansions of the energies in such cases. These include a
point-splitting prescription for expansions around the Dirichlet (fermionic)
limit of the -function potential, and performing a similarity
transformation to a non-Hermitian potential in the Calogero-Sutherland model.
As an application of the first technique, we study the ground state of the
-function Bose gas near the fermionic limit.Comment: LaTeX, 19 pages, no figure
ABJ(M) and Fractional M2's with Fractional M2 Charge
Recently Aharony, Bergman and Jafferis (ABJ) have argued that a 3d
U(N+M)xU(N) Chern-Simons gauge theory at level (k,-k) may have a vacuum with
N=6 supersymmetry only if M<k+1 and if a certain period of the B-field in a IIA
background is quantized. We use a braneology argument to argue that N=3
supersymmetry may be preserved under the weaker condition that 2Nk>M(M-k)-1
with no restriction on the B-field. IIB brane cartoons and 11d supergravity
solutions corresponding to N=3 vacua that do not preserve N=6 supersymmetry are
argued to represent cascading gauge theories, generalizing the N=2 Seiberg
duality conjectured by Giveon and Kutasov. While as usual the M2-brane charge
runs as a result of the twisted Bianchi identity for *G_4, the M5-brane charge
running relies on the fact that it wraps a torsion homology cycle.Comment: 16 pages, 3 eps figure
Chiral Condensate in Holographic QCD with Baryon Density
We consider the chiral condensate in the baryonic dense medium using the
generalized Sakai-Sugimoto model. It is defined as the vacuum expectation value
of open Wilson line that is proposed to be calculated by use of the area of
world-sheet instanton. We evaluate it in confined as well as deconfined phase.
In both phases, the chiral condensate has a minimum as a function of baryon
density. In the deconfined phase, taking into account the chiral symmetry
restoration, we classify the behavior of chiral condensate into three types.
One can set the parameter of the theory such that the results, in low but
sufficiently higher density, is in agreement with the expectation from QCD.Comment: 23 pages, 8 figure
Embedding massive flavor in ABJM
We add massive fundamental matter to the ABJM model by adding D6-branes
wrapped asymptotically over RP3. We find two types of solutions at finite
temperature, one that enters the black hole and one that ends before the black
hole. We analyze the behavior of the free energy as a function of temperature,
and find that the system exhibits a phase transition between the two types of
solutions, similar to what happens in the D3-D7 system. We also analyze the
meson spectrum in the model and find several massive scalar modes, again, quite
like the D3-D7 system. We end with a calculation of the conductivities in the
two phases.Comment: 26 pages, 6 figures; version published in JHE
Exactly stable non-BPS spinors in heterotic string theory on tori
Considering SO(32) heterotic string theory compactified on a torus of
dimension 4 and less, stability of non-supersymmetric states is studied. A
non-supersymmetric state with robust stability is constructed, and its exact
stability is proven in a large region of moduli space against all the possible
decay mechanisms allowed by charge conservation. Using various T-duality
transform matrices, we translate various selection rules about conserved
charges into simpler problems resembling partition and parity of integers. For
heterotic string on T^4, we give a complete list of BPS atoms with elementary
excitations, and we study BPS and non-BPS molecules with various binding
energies. Using string-string duality, the results are interpreted in terms of
Dirichlet-branes in type IIA string theory compactified on an orbifold limit of
a K3 surface.Comment: 47 pages, 14 figures, LaTe
Quark mass and condensate in HQCD
We extend the Sakai-Sugimoto holographic model of QCD (HQCD) by including the
scalar bi-fundamental "tachyon" field in the 8-brane-anti-8-brane probe theory.
We show that this field is responsible both for the spontaneous breaking of the
chiral symmetry, and for the generation of (current algebra) quark masses, from
the point of view of the bulk theory. As a by-product we show how this leads to
the Gell-Mann- Oakes-Renner relation for the pion mass.Comment: 23 pages, 7 figures; v2: corrected typos in eqs. (4.3), (4.4), (4.5),
(4.9) and (4.11), and corrected figures 3, 4, 5 and 6; v3: section 5.3 on the
pion mass rewritten in a clearer way, version published in JHE
Momentum modes of M5-branes in a 2d space
We study M5 branes by considering the selfdual strings parallel to a plane.
With the internal oscillation frozen, each selfdual string gives a 5d SYM
field. All selfdual strings together give a 6d field with 5 scalars, 3 gauge
degrees of freedom and 8 fermionic degrees of freedom in adjoint representation
of U(N). Selfdual strings with the same orientation have the SYM-type
interaction. For selfdual strings with the different orientations, which could
also be taken as the unparallel momentum modes of the 6d field on that plane or
the (p,q) (r,s) strings on D3 with (p,q)\neq (r,s), the [i,j]+[j,k]\rightarrow
[i,k] relation is not valid, so the coupling cannot be written in terms of the
standard N \times N matrix multiplication. 3-string junction, which is the
bound state of the unparallel [i,j] [j,k] selfdual strings, may play a role
here.Comment: 37 pages, 5 figures, to appear in JHEP; v2: reference adde
Zero-Mode Dynamics of String Webs
At sufficiently low energy the dynamics of a string web is dominated by zero
modes involving rigid motion of the internal strings. The dimension of the
associated moduli space equals the maximal number of internal faces in the web.
The generic web moduli space has boundaries and multiple branches, and for webs
with three or more faces the geometry is curved. Webs can also be studied in a
lift to M-theory, where a string web is replaced by a membrane wrapped on a
holomorphic curve in spacetime. In this case the moduli space is complexified
and admits a Kaehler metric.Comment: LaTeX, 17 pages, 5 eps figures; v2: references adde
Brane Dynamics and 3D Seiberg Duality on the Domain Walls of 4D N=1 SYM
We study a three-dimensional U(k) Yang-Mills Chern-Simons theory with adjoint
matter preserving two supersymmetries. According to Acharya and Vafa, this
theory describes the low-energy worldvolume dynamics of BPS domain walls in
four-dimensional N=1 SYM theory. We demonstrate how to obtain the same theory
in a brane configuration of type IIB string theory that contains threebranes
and fivebranes. A combination of string and field theory techniques allows us
to re-formulate some of the well-known properties of N=1 SYM domain walls in a
geometric language and to postulate a Seiberg-like duality for the Acharya-Vafa
theory. In the process, we obtain new information about the dynamics of branes
in setups that preserve two supersymmetries. Using similar methods we also
study other N=1 CS theories with extra matter in the adjoint and fundamental
representations of the gauge group.Comment: 25 pages, 5 figure
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