Karapet Mkrtchyan
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Research Subjects
Research Interests
Karapet Mkrtchyan has a total of 44 co-authors. Here are the top co-authors by number of shared publications:
- Euihun Joung
Kyung Hee University
21 shared publications Ruben Manvelyan
Department of Physics Erwin Schrödinger Straße Technical University of Kaiserslautern 3049 67653 Postfach Kaiserslautern Germany
11 shared publications- Oleg Evnin
Chulalongkorn University
8 shared publications - Stefan Fredenhagen
University of Vienna
7 shared publications - Werner Ruehl
Department of Physics Erwin Schrödinger Straße Technical University of Kaiserslautern 3049 67653 Postfach Kaiserslautern Germany
6 shared publications - Olaf Krüger
Faculty of Physics University of Vienna Boltzmanngasse 5 1090 Vienna Austria
5 shared publications
Latest Publications
- Open Access
- 12 November 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (11)
Metric-like cubic vertices for massless bosonic higher-spin fields in AdS3
A bstract: We derive parity-even transverse-traceless metric-like cubic vertices for massless bosonic higher-spin fields in AdS 3 . Starting from the known two- and three-derivative vertices in three-dimensional flat space, we construct their AdS 3 extensions by imposing gauge invariance and accounting for dimension-dependent identities. The result is shown to be consistent with minimal coupling to gravity.
- 12 November 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (11)
Open AccessMetric-like cubic vertices for massless bosonic higher-spin fields in AdS3
A bstract: We derive parity-even transverse-traceless metric-like cubic vertices for massless bosonic higher-spin fields in AdS 3 . Starting from the known two- and three-derivative vertices in three-dimensional flat space, we construct their AdS 3 extensions by imposing gauge invariance and accounting for dimension-dependent identities. The result is shown to be consistent with minimal coupling to gravity.
- Open Access
- 26 October 2026
- Published by American Physical Society (APS) in Physical Review D
- Vol. 114 (8) , 086019
Linearized gravity as edge modes and manifest duality and Lorentz covariance
We present the first formulation of linearized gravity in four dimensions which is manifestly Lorentz covariant and democratic, i.e., treats the two frames related by electric-magnetic duality on equal footing. It is well known that four-dimensional linearized gravity belongs to a class of singleton representations of the four-dimensional conformal algebra so ( 2 , 4 ) . Our key insight is viewing this algebra as the isometry of AdS 5 and realising the massless spin-2 field as edge modes of a five-dimensional topological field taking values in a specific finite-dimensional representation of so ( 2 , 4 ) . The desired four-dimensional action is then found by a covariant boundary reduction procedure.
- 26 October 2026
- Published by American Physical Society (APS) in Physical Review D
- Vol. 114 (8) , 086019
Open AccessLinearized gravity as edge modes and manifest duality and Lorentz covariance
We present the first formulation of linearized gravity in four dimensions which is manifestly Lorentz covariant and democratic, i.e., treats the two frames related by electric-magnetic duality on equal footing. It is well known that four-dimensional linearized gravity belongs to a class of singleton representations of the four-dimensional conformal algebra so ( 2 , 4 ) . Our key insight is viewing this algebra as the isometry of AdS 5 and realising the massless spin-2 field as edge modes of a five-dimensional topological field taking values in a specific finite-dimensional representation of so ( 2 , 4 ) . The desired four-dimensional action is then found by a covariant boundary reduction procedure.
- Open Access
- 21 May 2025
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2025 (5) , 1-26
Higher-order chiral scalar from boundary reduction of 3d higher-spin gravity
We use a recently proposed covariant procedure to reduce the Chern-Simons action of three-dimensional higher-spin gravity to the boundary, resulting in a Lorentz covariant action for higher-order chiral scalars. After gauge-fixing, we obtain a higher-derivative action generalizing the s = 1 Floreanini-Jackiw and s = 2 Alekseev-Shatashvili actions to arbitrary spin s. For simplicity, we treat the case of general spin at the linearized level, while the full non-linear asymptotic boundary conditions are presented in component form for the SL(3, ℝ) case. Finally, we extend the spin-3 linearized analysis to a background with non-trivial higher-spin charge and show that it has a richer structure of zero modes.
- 21 May 2025
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2025 (5) , 1-26
Open AccessHigher-order chiral scalar from boundary reduction of 3d higher-spin gravity
We use a recently proposed covariant procedure to reduce the Chern-Simons action of three-dimensional higher-spin gravity to the boundary, resulting in a Lorentz covariant action for higher-order chiral scalars. After gauge-fixing, we obtain a higher-derivative action generalizing the s = 1 Floreanini-Jackiw and s = 2 Alekseev-Shatashvili actions to arbitrary spin s. For simplicity, we treat the case of general spin at the linearized level, while the full non-linear asymptotic boundary conditions are presented in component form for the SL(3, ℝ) case. Finally, we extend the spin-3 linearized analysis to a background with non-trivial higher-spin charge and show that it has a richer structure of zero modes.
- Open Access
- 7 October 2024
- Published by American Physical Society (APS) in Physical Review D
- Vol. 110 (8)
Interactions of massless fermionic fields in three dimensions
All independent interaction vertices involving massless (Fang-Fronsdal) fermions in three dimensions are classified, completing the classification of interactions of massless fields of any spin. Similar to the bosonic case, we get no independent vertices at quartic or higher order in the fields involving fields with spin s ≥ 3 / 2 and cubic vertices only for spins satisfying triangle inequalities, apart from the cases involving (matter) fields with spin s ≤ 1 . Different from the bosonic cases, we get only one vertex for each triple of spins with two Majorana fermions and one boson, which is parity even (odd) when the sum of the spins of all fields involved is odd (even). When the two Majorana fermions are identical, their coupling to an odd-spin boson is trivialized. We comment on the nontrivial holographic dictionary relating these vertices to conformal field theory correlators in two dimensions. Published by the American Physical Society 2024
- 7 October 2024
- Published by American Physical Society (APS) in Physical Review D
- Vol. 110 (8)
Open AccessInteractions of massless fermionic fields in three dimensions
All independent interaction vertices involving massless (Fang-Fronsdal) fermions in three dimensions are classified, completing the classification of interactions of massless fields of any spin. Similar to the bosonic case, we get no independent vertices at quartic or higher order in the fields involving fields with spin s ≥ 3 / 2 and cubic vertices only for spins satisfying triangle inequalities, apart from the cases involving (matter) fields with spin s ≤ 1 . Different from the bosonic cases, we get only one vertex for each triple of spins with two Majorana fermions and one boson, which is parity even (odd) when the sum of the spins of all fields involved is odd (even). When the two Majorana fermions are identical, their coupling to an odd-spin boson is trivialized. We comment on the nontrivial holographic dictionary relating these vertices to conformal field theory correlators in two dimensions. Published by the American Physical Society 2024
- Open Access
- 3 June 2024
- Published by American Physical Society (APS) in Physical Review D
- Vol. 109 (12) , 125003
Spinor-helicity representations of particles of any mass in and spacetimesThe spinor-helicity representations of massive and (partially) massless particles in four-dimensional (anti–)de Sitter (A)dS spacetime are studied within the framework of the dual pair correspondence. We show that the dual groups (also known as “little groups”) of the anti–de Sitter and de Sitter groups are, respectively, and . For , the generator of the dual algebra corresponds to the helicity operator, and the spinor-helicity representation describes massless particles in (A). For , the dual algebra is composed of two ideals, and . The former ideal fixes the spin of the particle, while the mass is determined by the latter ideal , which is isomorphic to , , or depending on the cosmological constant being positive, zero, or negative. In the case of a positive cosmological constant, namely , the spinor-helicity representation contains all massive particles corresponding to the principal series representations and the partially massless particles corresponding to the discrete series representations leaving out only the light massive particles corresponding to the complementary series representations. The zero and negative cosmological constant cases, which had been addressed in earlier references, are also discussed briefly. Finally, we consider the multilinear form of helicity spinors invariant under (A)dS group, which can serve as the (A)dS counterpart of the scattering amplitude, and discuss technical differences and difficulties of the (A)dS cases compared to the flat spacetime case.- 3 June 2024
- Published by American Physical Society (APS) in Physical Review D
- Vol. 109 (12) , 125003
Open AccessSpinor-helicity representations of particles of any mass in and spacetimesThe spinor-helicity representations of massive and (partially) massless particles in four-dimensional (anti–)de Sitter (A)dS spacetime are studied within the framework of the dual pair correspondence. We show that the dual groups (also known as “little groups”) of the anti–de Sitter and de Sitter groups are, respectively, and . For , the generator of the dual algebra corresponds to the helicity operator, and the spinor-helicity representation describes massless particles in (A). For , the dual algebra is composed of two ideals, and . The former ideal fixes the spin of the particle, while the mass is determined by the latter ideal , which is isomorphic to , , or depending on the cosmological constant being positive, zero, or negative. In the case of a positive cosmological constant, namely , the spinor-helicity representation contains all massive particles corresponding to the principal series representations and the partially massless particles corresponding to the discrete series representations leaving out only the light massive particles corresponding to the complementary series representations. The zero and negative cosmological constant cases, which had been addressed in earlier references, are also discussed briefly. Finally, we consider the multilinear form of helicity spinors invariant under (A)dS group, which can serve as the (A)dS counterpart of the scattering amplitude, and discuss technical differences and difficulties of the (A)dS cases compared to the flat spacetime case. - Open Access
Interactions of massless fermionic fields in three dimensions
All independent interaction vertices involving massless (Fang--Fronsdal) fermions in three dimensions are classified, completing the classification of interactions of massless fields of any spin. Similarly to the bosonic case, we get no independent vertices at quartic or higher order in the fields involving fields with spin $s\geq 3/2$, and cubic vertices only for spins satisfying triangle inequalities, apart from the cases involving (matter) fields with spin $s\leq 1$. Differently from the bosonic cases, we get only one vertex for each triple of spins with two Majorana fermions and one boson, which is parity even (odd) when the sum of the spins of all fields involved is odd (even). When the two Majorana fermions are identical, their coupling to an odd-spin boson is trivialized. We comment on the non-trivial holographic dictionary relating these vertices to $CFT$ correlators in two dimensions.Open AccessInteractions of massless fermionic fields in three dimensions
All independent interaction vertices involving massless (Fang--Fronsdal) fermions in three dimensions are classified, completing the classification of interactions of massless fields of any spin. Similarly to the bosonic case, we get no independent vertices at quartic or higher order in the fields involving fields with spin $s\geq 3/2$, and cubic vertices only for spins satisfying triangle inequalities, apart from the cases involving (matter) fields with spin $s\leq 1$. Differently from the bosonic cases, we get only one vertex for each triple of spins with two Majorana fermions and one boson, which is parity even (odd) when the sum of the spins of all fields involved is odd (even). When the two Majorana fermions are identical, their coupling to an odd-spin boson is trivialized. We comment on the non-trivial holographic dictionary relating these vertices to $CFT$ correlators in two dimensions. - Open Access
- 28 March 2024
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2024 (3) , 1-32
On correlation functions of higher-spin currents in arbitrary dimensions d > 3
We revisit the problem of classification and explicit construction of the conformal three-point correlation functions of currents of arbitrary integer spin in arbitrary dimensions. For the conserved currents, we set up the equations for the conservation conditions and solve them completely for some values of spins, confirming the earlier counting of the number of independent structures matching them with the higher-spin cubic vertices in one higher dimension. The general solution for the correlators of conserved currents we delegate to a follow-up work.
- 28 March 2024
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2024 (3) , 1-32
Open AccessOn correlation functions of higher-spin currents in arbitrary dimensions d > 3
We revisit the problem of classification and explicit construction of the conformal three-point correlation functions of currents of arbitrary integer spin in arbitrary dimensions. For the conserved currents, we set up the equations for the conservation conditions and solve them completely for some values of spins, confirming the earlier counting of the number of independent structures matching them with the higher-spin cubic vertices in one higher dimension. The general solution for the correlators of conserved currents we delegate to a follow-up work.
- Open Access
- 5 March 2024
- Published by American Physical Society (APS) in Physical Review D
- Vol. 109 (6) , 066003
Democratic Lagrangians from topological bulk
Chiral form fields in dimensions can be effectively described as edge modes of topological Chern-Simons theories in dimensions. At the same time, manifestly Lorentz-invariant Lagrangian description of such fields directly in terms of a -dimensional field theory is challenging and requires introducing nontrivial auxiliary gauge fields eliminated on shell with extra gauge symmetries. A recent work by Arvanitakis et al. demonstrates (emphasizing the case of 2d chiral bosons) that the two approaches are related, and a peculiar reduction on the ()-dimensional topological Lagrangian automatically leads to -dimensional Lagrangians with appropriate sets of auxiliary fields. We develop this setup in three distinct directions. First, we demonstrate how arbitrary Abelian self-interactions for chiral forms can be included using nonlinear boundary terms in the Chern-Simons theory. Second, by generalizing the Chern-Simons theory to the BF-theory, we obtain an analogous democratic description of nonchiral form fields, where electric and magnetic potentials appear as explicit dynamical variables. Third, we discuss the effects of introducing topological interactions in the higher-dimensional bulk, which produce extra interaction terms in the boundary theory. When applied to a topological 4-form field in 12 dimensions, this construction results in a democratic description of the 3-form gauge field of the eleven-dimensional supergravity.- 5 March 2024
- Published by American Physical Society (APS) in Physical Review D
- Vol. 109 (6) , 066003
Open AccessDemocratic Lagrangians from topological bulk
Chiral form fields in dimensions can be effectively described as edge modes of topological Chern-Simons theories in dimensions. At the same time, manifestly Lorentz-invariant Lagrangian description of such fields directly in terms of a -dimensional field theory is challenging and requires introducing nontrivial auxiliary gauge fields eliminated on shell with extra gauge symmetries. A recent work by Arvanitakis et al. demonstrates (emphasizing the case of 2d chiral bosons) that the two approaches are related, and a peculiar reduction on the ()-dimensional topological Lagrangian automatically leads to -dimensional Lagrangians with appropriate sets of auxiliary fields. We develop this setup in three distinct directions. First, we demonstrate how arbitrary Abelian self-interactions for chiral forms can be included using nonlinear boundary terms in the Chern-Simons theory. Second, by generalizing the Chern-Simons theory to the BF-theory, we obtain an analogous democratic description of nonchiral form fields, where electric and magnetic potentials appear as explicit dynamical variables. Third, we discuss the effects of introducing topological interactions in the higher-dimensional bulk, which produce extra interaction terms in the boundary theory. When applied to a topological 4-form field in 12 dimensions, this construction results in a democratic description of the 3-form gauge field of the eleven-dimensional supergravity. - Open Access
Spinor-helicity representations of (A)dS$_4$ particles of any mass
The spinor-helicity representations of massive and (partially-)massless particles in four dimensional (Anti-) de Sitter spacetime are studied within the framework of the dual pair correspondence. We show that the dual groups (aka "little groups") of the AdS and dS groups are respectively $O(2N)$ and $O^*(2N)$. For $N=1$, the generator of the dual algebra $\mathfrak{so}(2)\cong \mathfrak{so}^*(2) \cong \mathfrak{u}(1)$ corresponds to the helicity operator, and the spinor-helicity representation describes massless particles in (A)dS$_4$. For $N=2$, the dual algebra is composed of two ideals, $\mathfrak{s}$ and $\mathfrak{m}_Λ$. The former ideal $\mathfrak{s}\cong \mathfrak{so}(3)$ fixes the spin of the particle, while the mass is determined by the latter ideal $\mathfrak{m}_Λ$, which is isomorphic to $\mathfrak{so}(2,1)$, $\mathfrak{iso}(2)$ or $\mathfrak{so}(3)$ depending on the cosmological constant being positive, zero or negative. In the case of a positive cosmological constant, namely dS$_4$, the spinor-helicity representation contains all massive particles corresponding to the principal series representations and the partially-massless particles corresponding to the discrete series representations leaving out only the light massive particles corresponding to the complementary series representations. The zero and negative cosmological constant cases, which had been addressed in earlier references, are also discussed briefly. Finally, we consider the multilinear form of helicity spinors invariant under (A)dS group, which can be served for the (A)dS counterpart of the scattering amplitude, and discuss technical differences and difficulties of the (A)dS cases compared to the flat spacetime case.Open AccessSpinor-helicity representations of (A)dS$_4$ particles of any mass
The spinor-helicity representations of massive and (partially-)massless particles in four dimensional (Anti-) de Sitter spacetime are studied within the framework of the dual pair correspondence. We show that the dual groups (aka "little groups") of the AdS and dS groups are respectively $O(2N)$ and $O^*(2N)$. For $N=1$, the generator of the dual algebra $\mathfrak{so}(2)\cong \mathfrak{so}^*(2) \cong \mathfrak{u}(1)$ corresponds to the helicity operator, and the spinor-helicity representation describes massless particles in (A)dS$_4$. For $N=2$, the dual algebra is composed of two ideals, $\mathfrak{s}$ and $\mathfrak{m}_Λ$. The former ideal $\mathfrak{s}\cong \mathfrak{so}(3)$ fixes the spin of the particle, while the mass is determined by the latter ideal $\mathfrak{m}_Λ$, which is isomorphic to $\mathfrak{so}(2,1)$, $\mathfrak{iso}(2)$ or $\mathfrak{so}(3)$ depending on the cosmological constant being positive, zero or negative. In the case of a positive cosmological constant, namely dS$_4$, the spinor-helicity representation contains all massive particles corresponding to the principal series representations and the partially-massless particles corresponding to the discrete series representations leaving out only the light massive particles corresponding to the complementary series representations. The zero and negative cosmological constant cases, which had been addressed in earlier references, are also discussed briefly. Finally, we consider the multilinear form of helicity spinors invariant under (A)dS group, which can be served for the (A)dS counterpart of the scattering amplitude, and discuss technical differences and difficulties of the (A)dS cases compared to the flat spacetime case. - Open Access
Democracy from topology
Chiral form fields in $d$ dimensions can be effectively described as edge modes of topological Chern-Simons theories in $d+1$ dimensions. At the same time, manifestly Lorentz-invariant Lagrangian description of such fields directly in terms of a $d$-dimensional field theory is challenging and requires introducing nontrivial auxiliary gauge fields eliminated on-shell with extra gauge symmetries. A recent work by Arvanitakis et al.\ demonstrates (emphasizing the case of 2d chiral bosons) that the two approaches are related, and a peculiar reduction on the $(d+1)$-dimensional topological Lagrangian automatically leads to $d$-dimensional Lagrangians with appropriate sets of auxiliary fields. We develop this setup in three distinct directions. First, we demonstrate how arbitrary Abelian self-interactions for chiral forms can be included using nonlinear boundary terms in the Chern-Simons theory. Second, by generalizing the Chern-Simons theory to the BF theory, we obtain an analogous democratic description of non-chiral form fields, where electric and magnetic potentials appear as explicit dynamical variables. Third, we discuss the effects of introducing topological interactions in the higher-dimensional bulk, which produce extra interaction terms in the boundary theory. When applied to a topological 4-form field in 12 dimensions, this construction results in a democratic description of the 3-form gauge field of the 11-dimensional supergravity.Open AccessDemocracy from topology
Chiral form fields in $d$ dimensions can be effectively described as edge modes of topological Chern-Simons theories in $d+1$ dimensions. At the same time, manifestly Lorentz-invariant Lagrangian description of such fields directly in terms of a $d$-dimensional field theory is challenging and requires introducing nontrivial auxiliary gauge fields eliminated on-shell with extra gauge symmetries. A recent work by Arvanitakis et al.\ demonstrates (emphasizing the case of 2d chiral bosons) that the two approaches are related, and a peculiar reduction on the $(d+1)$-dimensional topological Lagrangian automatically leads to $d$-dimensional Lagrangians with appropriate sets of auxiliary fields. We develop this setup in three distinct directions. First, we demonstrate how arbitrary Abelian self-interactions for chiral forms can be included using nonlinear boundary terms in the Chern-Simons theory. Second, by generalizing the Chern-Simons theory to the BF theory, we obtain an analogous democratic description of non-chiral form fields, where electric and magnetic potentials appear as explicit dynamical variables. Third, we discuss the effects of introducing topological interactions in the higher-dimensional bulk, which produce extra interaction terms in the boundary theory. When applied to a topological 4-form field in 12 dimensions, this construction results in a democratic description of the 3-form gauge field of the 11-dimensional supergravity.