arXiv subjects

Daniel L. Nedel

Publications and source records attributed to Daniel L. Nedel.

At least 19 recordsLinked to original sources

arXiv2021

Quantization of Open strings in time dependent Black Holes

In this letter, the open string is quantized in a time dependent black hole background. The geometry is defined through an adiabatic approximation of the Vaydia metric. The worldsheet two-point function is derived and it is shown to have the same type of singularity as the flat space one. However, the equal times two-point function depends on the particular Cauchy surface where the worldsheet fields are defined. Finite temperature effects are incorporated through the Liouville-von Neumann approach to non equilibrium thermodynamics.

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arXiv2021

Entanglement Entropy from TFD Entropy Operator

In this work, a canonical method to compute entanglement entropy is proposed. We show that for two-dimensional conformal theories defined in a torus, a choice of moduli space allows the typical entropy operator of the TFD to provide the entanglement entropy of the degrees of freedom defined in a segment and their complement. In this procedure, it is not necessary to make an analytic continuation from the Rényi entropy and the von Neumann entanglement entropy is calculated directly from the expected value of an entanglement entropy operator. We also propose a model for the evolution of the entanglement entropy and show that it grows linearly with time.

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arXiv2021

Time dependent Entanglement Entropy in dissipative conformal theories: TFD approach

In this work the TFD formalism is explored in order to study a dissipative time-dependent thermal vacuum. This state is a consequence of a particular interaction between two theories, which can be interpreted as two conformal theories defined at the two asymptotic boundaries of an AdS black hole. The initial state is prepared to be the equilibrium TFD thermal vacuum. The interaction causes dissipation from the point of view of observers who measure observables in one of the boundaries. We show that the vacuum evolves as an entangled state at finite temperature and the dissipative dynamics is controlled by the time-dependent entropy operator, defined in the non-equilibrium TFD framework. We use lattice field theory techniques to calculate the non-equilibrium thermodynamic entropy and the finite temperature entanglement entropy. We show that both grow linearly with time.

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arXiv2020

Time dependent Entanglement Entropy in SYK models and Page Curve

In this work new interaction terms between two SYK models are proposed, which allow to define an interaction picture such that it is possible to calculate exactly the vacuum state's time evolution. It is shown that the vacuum evolves as a time dependent $SU(2)$ squezed state. The time dependent entanglement entropy is calculated and it has the same form of the Page curve of Black Hole formation and evaporation.

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arXiv2012

Supergraph Approach in a Higher-order LDE Calculation of the Effective Potential for F-type Broken SUSY

In this work, we adopt the simplest model that spontaneously breaks supersymmetry, namely, the minimal O'Raifeartaigh model. The effective potential is computed in the framework of the linear delta expansion (LDE) approach up to the order $δ^2$, conjugated with superspace and supergraph techniques. The latter can be duly mastered even if supersymmetry is no longer exact and the efficacy of the superfield approach in connection with the LDE procedure is confirmed according to our investigation. That opens up a way for a semi-nonperturbative superspace computation which allows us to deal with spontaneously broken supersymmetric models and encourages us to go further and apply this treatment to the Minimal Supersymmetric Standard Model (MSSM) precision tests.

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arXiv2012

Superspace approach to the renormalization of the O'Raifeartaigh model up to the second order in the LDE parameter

We adopt a superspace/supergraph formalism to pursue the investigation of the structure of one- and two-loop divergences in the frame of the minimal O'Raifeartaigh model that realizes the F-term spontaneous supersymmetry breaking. The linear delta expansion(LDE) procedure is introduced and renormalization is carried out up to the second order in the LDE expansion parameter. In agreement with the nonrenormalization theorem for the (chiral/antichiral) matter potential of ${\mathcal N}=1, \ D=4$ supersymmetry, our explicit supergraph calculations confirm that only the Kähler potential is actually renomalized.

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arXiv2010

Superspace evaluation of the two-loop effective potential for the O'Raifeartaigh model

All-order spurion-corrected superpropagators and superfield Feynman rules are employed to systematically compute a two-loop corrected effective potential for the O'Raifeartaigh model, that realizes spontaneous supersymmetry breaking. Though the shifted superpropagators are rather nontrivial, superspace techniques may be suitably extended and confirm their efficacy in computing radiative corrections even when supersymmetry breakdown occurs.

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arXiv2010

Quantum Current Algebra for the $AdS_5 \times S^5$ Superstring

The sigma model describing the dynamics of the superstring in the $AdS_5 \times S^5$ background can be constructed using the coset $PSU(2,2|4)/SO(4,1)\times SO(5)$. A basic set of operators in this two dimensional conformal field theory is composed by the left invariant currents. Since these currents are not (anti) holomorphic, their OPE's is not determined by symmetry principles and its computation should be performed perturbatively. Using the pure spinor sigma model for this background, we compute the one-loop correction to these OPE's. We also compute the OPE's of the left invariant currents with the energy momentum tensor at tree level and one loop.

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arXiv2009

Linear delta expansion applied to the O'Raifeartaigh model

We reassess the method of the linear delta expansion for the calculation of effective potentials in superspace, by adopting the improved version of the super-Feynman rules in the framework of the O'Raifeartaigh model for spontaneous supersymmetry breaking. The effective potential is calculated using both the fastest apparent convergence and the principle of minimal sensitivity criteria and the consistency and efficacy of the method are checked in deriving the Coleman-Weinberg potential.

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arXiv2008

Observer dependent D-brane for strings propagating in pp-wave time dependent background

We study type IIB superstring in the pp-wave time-dependent background, which has a singularity at $t=0$. We show that this background can provide a toy model to study some ideas related to the stretched horizon paradigm and the complementary principle of black holes. To this end, we construct a unitary Bogoliubov generator which relates the asymptotically flat string Hilbert space, defined at $t =\pm \infty$, to the finite time Hilbert space. For asymptotically flat observers, the closed string vacuum close to the singularity appears as a boundary state which is in fact a D-brane described in the closed string channel. However, observers who go with the string towards to the singularity see the original vacuum.

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arXiv2007

An extension of the Linear Delta Expansion to Superspace

We introduce and discuss the method of Linear Delta Expansion for the calculation of effective potentials in superspace, by adopting the improved version of the super-Feynman rules. Calculations are carried out up to two-loops and an expression for the optimized Kähler potential is worked out.

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arXiv2006

Entanglement and entropy operator for strings in pp-wave time dependent background

In this letter new aspects of string theory propagating in a pp-wave time dependent background with a null singularity are explored. It is shown the appearance of a 2d entanglement entropy dynamically generated by the background. For asymptotically flat observers, the vacuum close to the singularity is unitarily inequivalent to the vacuum at $τ= -\infty$ and it is shown that the 2d entanglement entropy diverges close to this point. As a consequence, the positive time region is inaccessible for observers in $τ=-\infty$. For a stationary measure, the vacuum at finite time is seen by those observers as a thermal state and the information loss is encoded as a heat bath of string states.

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arXiv2005

PP-Wave Light-Cone Free String Field Theory at Finite Temperature

In this paper, a real-time formulation of light-cone pp-wave string field theory at finite temperature is presented. This is achieved by developing the thermo field dynamics (TFD) formalism in a second quantized string scenario. The equilibrirum thermodynamic quantities for a pp-wave ideal string gas are derived directly from expectation values on the second quantized string thermal vacuum. Also, we derive the real-time thermal pp-wave closed string propagator. In the flat space limit it is shown that this propagator can be written in terms of Theta functions, exactly as the zero temperature one. At the end, we show how supestrings interactions can be introduced, making this approach suitable to study the BMN dictionary at finite temperature.

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arXiv2005

Closed String Thermal Torus From Thermo Field Dynamics

In this Letter a topological interpretation for the string thermal vacuum in the Thermo Field Dynamics (TFD) approach is given. As a consequence, the relationship between the Imaginary Time and TFD formalisms is achieved when both are used to study closed strings at finite temperature. The TFD approach starts by duplicating the system's degrees of freedom, defining an auxiliary (tilde) string. In order to lead the system to finite temperature a Bogoliubov transformation is implemented. We show that the effect of this transformation is to glue together the string and the tilde string to obtain a torus. The thermal vacuum appears as the boundary state for this identification. Also, from the thermal state condition, a Kubo-Martin-Schwinger condition for the torus topology is derived.

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arXiv2004

General Unitary TFD Formulation for Superstrings

A generalization of the Thermo Field Dynamics (TFD) for fermionic degrees of freedom is proposed. Such a generalization follows a previous one where the SU(1,1) thermal group was used to obtain the closed bosonic string at finite temperature. The SU(2) thermal group is introduced to construct a general thermal Bogoliubov transformation to get the type IIB superstring at finite temperature.

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arXiv2004

Perspectives of TFD on String Theory

Considering the type IIB superstring in a pp wave background some recent ideas and perspectives of Thermo Field Dynamics on string theory are presented. The thermal Fock space is constructed attempting to consider a possible finite temperature version of the BMN correspondence in this framework. Also, the thermal vacuum is identified as a string boundary state realizing the thermal torus interpretation in the ambit of Thermo Field Dynamics. Such a interpretation consists of a generalization of some recent analysis for the closed bosonic string.

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arXiv2004

Superspace Type II 4D Supergravity from Type II Superstring

We derive the equations of motion of type II 4D supergravity in superspace. This is achieved by coupling the Type II Berkovits' hybrid superstring to an N=2 curved background and requiring that the sigma-model has N=(2,2) superconformal invariance at one loop. We show that there are no anomalies in the fermionic OPE's and the complete set of compensator's equations is derived from the energy-momentum tensor. The equations of motion describe a hypertensorial and vectorial multiplet coupled to a U(1)\times U(1) N=2 Poincarè Supergravity.

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arXiv2004

On the entropy operator for the general SU(1,1) TFD formulation

In this letter, an entropy operator for the general unitary SU(1,1) TFD formulation is proposed and used to lead a bosonic system from zero to finite temperature. Namely, considering the closed bosonic string as the target system, the entropy operator is used to construct the thermal vacuum. The behaviour of such a state under the breve conjugation rules is analized and it was shown that the breve conjugation does not affect thermal effects. From this thermal vacuum the thermal energy, the entropy and the free energy of the closed bosonic string are calculated and the apropriated thermal distribution for the system is found after the free energy minimization.

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