SEARCH · Search arXiv

Results for “hep-th”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources

arXiv2011

Towards a holographic marginal Fermi liquid

We present an infinite class of 2+1 dimensional field theories which, after coupling to semi-holographic fermions, exhibit strange metallic behavior in a suitable large $N$ limit. These theories describe lattices of hypermultiplet defects interacting with parity-preserving supersymmetric Chern-Simons theories with $U(N) \times U(N)$ gauge groups at levels $\pm k$. They have dual gravitational descriptions in terms of lattices of probe M2 branes in $AdS_4 \times S^7/Z_k$ (for $N \gg 1, N \gg k^5$) or probe D2 branes in $AdS_4 \times CP^3$ (for $N \gg k \gg 1, N \ll k^5$). We discuss several challenges one faces in maintaining the success of these models at finite $N$, including backreaction of the probes in the gravity solutions and radiative corrections in the weakly coupled field theory limit.

hep-th↗

arXiv2011

Near-horizon solutions for D3-branes ending on 5-branes

We construct the type IIB supergravity solutions describing D3-branes ending on 5-branes, in the near-horizon limit of the D3-branes. Our solutions are holographically dual to the 4d N=4 SU(N) super-Yang-Mills (SYM) theory on a half-line, at large N and large 't Hooft coupling, with various boundary conditions that preserve half of the supersymmetry. The solutions are limiting cases of the general solutions with the same symmetries constructed in 2007 by D'Hoker, Estes and Gutperle. The classification of our solutions matches exactly with the general classification of boundary conditions for D3-branes ending on 5-branes by Gaiotto and Witten. We use the gravity duals to compute the one-point functions of some chiral operators in the N=4 SYM theory on a half-line at strong coupling, and find that they do not match with the expectation values of the same operators with the same boundary conditions at small 't Hooft coupling. Our solutions may also be interpreted as the gravity duals of 4d N=4 SYM on AdS_4, with various boundary conditions.

hep-th↗

arXiv2011

Model building in AdS/CMT: DC conductivity and Hall angle

Using the bottom-up approach in a holographic setting, we attempt to study both the transport and thermodynamic properties of a generic system in 3+1 dimensional bulk spacetime. We show the exact 1/T and $T^2$ dependence of the longitudinal conductivity and Hall angle, as seen experimentally in most copper-oxide systems, which are believed to be close to quantum critical point. This particular temperature dependence to conductivities are possible in two different cases: (1) Background solutions with scale invariant and broken rotational symmetry, (2) solutions with pseudo-scaling and unbroken rotational symmetry but only at low density limit. Generically, the study of the transport properties in a scale invariant background solution, using the probe brane approach, at high density and at low temperature limit suggests us to consider only metrics with two exponents. More precisely, the spatial part of the metric components should not be same i.e., $g_{xx}\neq g_{yy}$. In doing so, we have generated the above mentioned behavior to conductivity with a very special behavior to specific heat which at low temperature goes as: $C_V\sim T^3$. However, if we break the scaling symmetry of the background solution by including a nontrivial dilaton, axion or both and keep the rotational symmetry then also we can generate such a behavior to conductivity but only in the low density regime. As far as we are aware, this particular temperature dependence to both the conductivity and Hall angle is being shown for the first time using holography.

hep-th↗

arXiv2011

Decay widths of large-spin mesons from the non-critical string/gauge duality

In this paper, we use the non-critical string/gauge duality to calculate the decay widths of large-spin mesons. Since it is believed that the string theory of QCD is not a ten dimensional theory, we expect that the non-critical versions of ten dimensional black hole backgrounds lead to better results than the critical ones. For this purpose we concentrate on the confining theories and consider two different six dimensional black hole backgrounds. We choose the near extremal AdS6 model and the near extremal KM model to compute the decay widths of large-spin mesons. Then, we present our results from these two non-critical backgrounds and compare them together with those from the critical models and experimental data.

hep-th↗

arXiv2010

Helical Luttinger Liquids and Three Dimensional Black Holes

Cold interacting fermions in two dimensions form exactly solvable Luttinger liquids, whose characteristic scaling exponents differ from those of conventional Fermi liquids. We use the AdS/CFT correspondence to discuss an equivalence between a class of helical, strongly coupled Luttinger liquids and fermions propagating in the background of a 3D black hole. The microscopic Lagrangian is explicitly known and the construction is fully embeddable in string theory. The retarded Green function at low temperature and energy arises from the geometry very near the black hole horizon. This structure is universal for all cold, charged liquids with a dual description in gravity.

hep-th↗

arXiv2011

Dynamic critical phenomena at a holographic critical point

We study time-dependent perturbations to a family of five-dimensional black hole spacetimes constructed as a holographic model of the QCD phase diagram. We use the results to calculate two transport coefficients, the bulk viscosity and conductivity, as well as the associated baryon diffusion constant, throughout the phase diagram. Near the critical point in the T-mu plane, the transport coefficients remain finite, although their derivatives diverge, and the diffusion goes to zero. This provides further evidence that large-N_c gauge theories suppress convective transport. We also find a divergence in the low-temperature bulk viscosity, outside the region expected to match QCD, and compare the results to the transport behavior of known R-charged black holes.

hep-th↗

arXiv2011

Equivalence of Wilson Loops in ABJM and N = 4 SYM Theory

In previous investigations, it was found that four-sided polygonal light-like Wilson loops in ABJM theory calculated to two-loop order have the same form as the corresponding Wilson loop in N = 4 SYM at one-loop order. Here we study light-like polygonal Wilson loops with n cusps in planar three-dimensional Chern-Simons and ABJM theory to two loops. Remarkably, the result in ABJM theory precisely agrees with the corresponding Wilson loop in N = 4 SYM at one-loop order for arbitrary n. In particular, anomalous conformal Ward identites allow for a so-called remainder function of conformal cross ratios, which is found to be trivial at two loops in ABJM theory in the same way as it is trivial in N = 4 SYM at one-loop order. Furthermore, the result for arbitrary n obtained here, allows for a further investigation of a Wilson loop / amplitude duality in ABJM theory, for which non-trivial evidence was recently found by a calculation of four-point amplitudes that match the Wilson loop in ABJM theory.

hep-th↗

arXiv2011

Holographic Wilsonian Renormalization and Chiral Phase Transitions

We explore the role of a holographic Wilsonian cut-off in simple probe brane models with chiral symmetry breaking/restoration phase transitions. The Wilsonian cut-off allows us to define supergravity solutions for off-shell configurations and hence to define a potential for the chiral condensate. We pay particular attention to the need for configurations whose action we are comparing to have the same IR and UV boundary conditions. We exhibit new first and second order phase transitions with changing cut-off. We derive the effective potential for the condensate including mean field and BKT type continuous transitions.

hep-th↗

arXiv2011

Two-loop corrections to partition function of Pohlmeyer-reduced theory for AdS_5 x S^5 superstring

Pohlmeyer reduction of AdS_5 x S^5 superstring leads to a set of equations of motion following from an action containing a bosonic Sp(2,2) x Sp(4)/[SU(2)]^4 gauged WZW term, an integrable potential and a fermionic part coupling bosons from the two factors. The original superstring and the reduced model are in direct correspondence at the classical level but their relation at the quantum level remains an open question. As was found earlier, the one-loop partition functions of the two theories computed on the respective classical backgrounds match; here we explore the fate of this relation at the two-loop level. We consider the example of the reduced theory solution corresponding to the long folded spinning string in AdS. The logarithm of the AdS_5 x S^5 superstring partition function computed on the spinning string background is known to be proportional to the universal scaling function which depends on the string tension ~ ł^{1/2} where ł=λis `t Hooft coupling. Its "quantum" part is f(ł) = a1 + ł^{-1/2} a2 + ... where the one-loop term is a1 = - 3 \ln 2 and the two-loop term is minus the Catalan's constant, a2=-K. We find that the counterpart of f(ł) in the reduced theory is f'(k) =a1' + 2 k^{-1} a2' + ..., where k is the coupling of the reduced theory. Here the one-loop coefficient is the same as in the string theory, a1'= a1, while the two-loop one is a2' =a2 - 1/4 (a1)^2. Remarkably, the first Catalan's constant term here matches the string theory result if we identify the two couplings as k= 2ł^{1/2}. Nevertheless, the presence of the additional (a1)^2 ~ (\ln 2)^2 term implies that a relation between the two quantum partition functions (if any) is not a simple equality. Similar results are found in the case of AdS_3 x S^3 superstring theory where a1= - 2 \ln 2 and a2=0, while in the corresponding reduced theory a1'=a1, a2'= a2- 1/4 (a1)^2.

hep-th↗

arXiv2011

Constraint on the Low Energy Constants of Wilson Chiral Perturbation Theory

Wilson chiral perturbation theory (WChPT) is the effective field theory describing the long- distance properties of lattice QCD with Wilson or twisted-mass fermions. We consider here WChPT for the theory with two light flavors of Wilson fermions or a single light twisted-mass fermion. Discretization errors introduce three low energy constants (LECs) into partially quenched WChPT at O(a^2), conventionally called W'_6, W'_7 and W'_8 . The phase structure of the theory at non-zero a depends on the sign of the combination 2W'_6 + W'_8, while the spectrum of the lattice Hermitian Wilson-Dirac operator depends on all three constants. It has been argued, based on the positivity of partition functions of fixed topological charge, and on the convergence of graded group integrals that arise in the epsilon-regime of ChPT, that there is a constraint on the LECs arising from the underlying lattice theory. In particular, for W'_6 = W'_7 = 0, the constraint found is W'_8 \le 0. Here we provide an alternative line of argument, based on mass inequalities for the underlying partially quenched theory. We find that W'_8 \le 0, irrespective of the values of W'_6 and W'_7. Our constraint implies that 2W'_6 > |W'_8| if the phase diagram is to be described by the first-order scenario, as recent simulations suggest is the case for some choices of action.

hep-lat↗

arXiv2011

SUSY Hidden in the Continuum

We study models where the superpartners of the ordinary particles have continuous spectra rather than being discrete states, which can occur when the supersymmetric standard model is coupled to an approximately conformal sector. We show that when superpartners that are well into the continuum are produced at a collider they tend to have long decay chains that step their way down through the continuum, emitting many fairly soft standard model particles along the way, with a roughly spherical energy distribution in the center of mass frame.

hep-ph↗

arXiv2011

New relations for scattering amplitudes in Yang-Mills theory at loop level

The calculation of scattering amplitudes in Yang-Mills theory at loop level is important for the analysis of background processes at particle colliders as well as our understanding of perturbation theory at the quantum level. We present tools to derive relations for especially one loop amplitudes, as well as several explicit examples for gauge theory coupled to a wide variety of matter. These tools originate in certain scaling behavior of permutation and cyclic sums of Yang-Mills tree amplitudes and loop integrands. In the latter case evidence exists for relations at all loop orders.

hep-th↗

arXiv2011

Particle propagation and effective space-time in Gravity's Rainbow

Basing on the results obtained in a our previous study on Gravity's Rainbow, we determine the quantum corrections to the space-time metric for the Schwarzschild and the de Sitter background, respectively. We analyze how quantum fluctuations alter these metrics inducing modifications on the propagation of test particles. Significantly enough we find that quantum corrections can become relevant not only for particles approaching the Planck energy but, due to the one loop contribution, even for low-energy particles as far as Planckian length scales are considered. We briefly compare our results with others obtained in similar studies and with the recent experimental OPERA announcement of superluminal neutrino propagation.

gr-qc↗

arXiv2011

Stability of superconducting strings coupled to cosmic strings

We study the stability of superconducting strings in a U(1)_{local} x U(1)_{global} model coupled via a gauge field interaction term to U(1) Abelian-Higgs strings. The effect of the interaction on current stability is numerically investigated by varying the relevant parameters within the physical limits of our model. We find that the propagation speed of transverse (resp. longitudinal) perturbations increases (decreases) with increasing binding between the superconducting and Abelian-Higgs string. Moreover, we observe that for small enough width of the flux tube of the superconducting string and/or large enough interaction between the superconducting and the Abelian-Higgs string superconducting strings cannot carry space-like, i.e. magnetic currents. Our model can be seen as a field theoretical realization of bound states of p F-strings and q superconducting D-strings and has important implications to vorton formation during the evolution of networks of such strings.

hep-th↗

arXiv2011

Gauge Field Production in Axion Inflation: Consequences for Monodromy, non-Gaussianity in the CMB, and Gravitational Waves at Interferometers

Models of inflation based on axions, which owe their popularity to the robustness against UV corrections, have also a very distinct class of signatures. The relevant interactions of the axion are a non-perturbative oscillating contribution to the potential and a shift-symmetric coupling to gauge fields. We review how these couplings affect the cosmological perturbations via a unified study based on the in-in formalism. We then note that, when the inflaton coupling to gauge fields is high enough to lead to interesting observational results, the backreaction of the produced gauge quanta on the inflaton dynamics becomes relevant during the final stage of inflation, and prolongs its duration by about 10 e-foldings. We extend existing results on gravity wave production in these models to account for this late inflationary phase. The strong backreaction phase results in an enhancement of the gravity wave signal at the interferometer scales. As a consequence, the signal is potentially observable at Advanced LIGO/VIRGO for the most natural duration of inflation in such models. Finally, we explicitly compute the axion couplings to gauge fields in string theory construction of axion monodromy inflation and identify cases where they can trigger interesting phenomenological effects.

astro-ph.CO↗

arXiv2012

Introduction of the generalized Lorenz gauge condition into the vector-tensor theory

We introduce the generalized Lorentz gauge condition in the theory of quantum electrodynamics into the general vector-tensor theories of gravity. Then we explore the cosmic evolution and the static, spherically symmetric solution of the four dimensional vector field with the generalized Lorenz gauge. We find that, if the vector field is minimally coupled to the gravitation, it behaves as the cosmological constant. On the other hand, if it is nonminimally coupled to the gravitation, the vector field could behave as vast matters in the background of spatially flat Friedmann-Robertson-Walker Universe. But it may be not the case. The weak, strong and dominant energy conditions, the stability analysis of classical and quantum aspects would put constraints on the parameters and so the equation of state of matters would be greatly constrained.

gr-qc↗

arXiv2011

Hawking radiation for a Proca field in D-dimensions

We study the wave equation of a massive vector boson in the background of a D-dimensional Schwarzschild black hole. The mass term introduces a coupling between two physical degrees of freedom of the field, and we solve the resulting system of ODEs numerically, without decoupling. We show how to define decoupled transmission factors from an S-matrix and compute them for various modes, masses and space-time dimensions. The mass term lifts the degeneracy between transverse modes, in D=4, and excites the longitudinal modes, in particular the s-wave. Moreover, it increases the contribution of waves with larger angular momentum, which can be dominant at intermediate energies. The transmission factors are then used to obtain the Hawking fluxes in this channel. Our results alert for the importance of modelling the longitudinal modes correctly, instead of treating them as decoupled scalars as in current black hole event generators; thus they can be used to improve such generators for phenomenological studies of TeV gravity scenarios.

gr-qc↗

arXiv2012

Oscillating instanton solutions in curved space

We investigate oscillating instanton solutions of a self-gravitating scalar field between degenerate vacua. We show that there exist O(4)-symmetric oscillating solutions in a de Sitter background. The geometry of this solution is finite and preserves the $Z_{2}$ symmetry. The nontrivial solution corresponding to tunneling is possible only if the effect of gravity is taken into account. We present numerical solutions of this instanton, including the phase diagram of solutions in terms of the parameters of the present work and the variation of energy densities. Our solutions can be interpreted as solutions describing an instanton-induced domain wall or braneworld-like object rather than a kink-induced domain wall or braneworld. The oscillating instanton solutions have a thick wall and the solutions can be interpreted as a mechanism providing nucleation of the thick wall for topological inflation. We remark that $Z_{2}$ invariant solutions also exist in a flat and anti-de Sitter background, though the physical significance is not clear.

hep-th↗