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N. Itzhaki

Publications and source records attributed to N. Itzhaki.

At least 19 recordsLinked to original sources
arXiv2024

When Strings Surprise

We argue that on-shell excitations with large negative energies are created rapidly when the string coupling increases with time. This does not indicate an inconsistency in string theory since the negative energy on-shell excitation is always entangled with an on-shell excitation with a positive energy. The total energy of this energy-EPR state vanishes. We discuss the reason the energy-EPR states appear in string theory and the role they might play in black hole physics.

hep-th↗
arXiv2012

Constraints on the Neutrino Mass from SZ Surveys

Statistical measures of galaxy clusters are sensitive to neutrino masses in the sub-eV range. We explore the possibility of using cluster number counts from the ongoing PLANCK/SZ and future cosmic-variance-limited surveys to constrain neutrino masses from CMB data alone. The precision with which the total neutrino mass can be determined from SZ number counts is limited mostly by uncertainties in the cluster mass function and intracluster gas evolution; these are explicitly accounted for in our analysis. We find that projected results from the PLANCK/SZ survey can be used to determine the total neutrino mass with a (1σ) uncertainty of 0.06 eV, assuming it is in the range 0.1-0.3 eV, and the survey detection limit is set at the 5σsignificance level. Our results constitute a significant improvement on the limits expected from PLANCK/CMB lensing measurements, 0.15 eV. Based on expected results from future cosmic-variance-limited (CVL) SZ survey we predict a 1σuncertainty of 0.04 eV, a level comparable to that expected when CMB lensing extraction is carried out with the same experiment. A few percent uncertainty in the mass function parameters could result in up to a factor \sim 2-3 degradation of our PLANCK and CVL forecasts. Our analysis shows that cluster number counts provide a viable complementary cosmological probe to CMB lensing constraints on the total neutrino mass.

astro-ph.CO↗
arXiv2004

The Horizon Order Parameter

We construct a diffeormorphism invariant operator that is sensitive to how far we are from the black hole horizon. Its expectation value blows up on the horizon and it is small away from the horizon. Using this operator, we propose a non-standard effective action that, we argue, captures some of the relevant physics of quantum black holes, including the absence of the horizon at the full quantum level. With the help of a toy version of this effective action, we speculate on a possible connection between UV/IR mixing and the cosmological constant problem.

hep-th↗
arXiv2002

Anyons, 't Hooft loops and a Generalized Connection in Three Dimensions

We consider a generalized connection in three dimensions and show that it emerges in Chern-Simons-Maxwell theories when one studies the disorder instanton operator. We generalize this construction to non-Abelian theories and find that the disorder operator (the 't Hooft operator) is equivalent to a generalized Wilson loop in a representation that depends on the Chern-Simons term. We speculate about the effective action of the disorder operator and its applications to the possible phases of the theory in the infra-red. We also show that fractional statistics can emerge in gauge theories without a Chern-Simons term if the generalized connection rather than the ordinary connection is used to couple charged particles.

hep-th↗
arXiv2002

PP Wave Limit and Enhanced Supersymmetry in Gauge Theories

We observe that the pp wave limit of $AdS_5\times M^5$ compactifications of type IIB string theory is universal, and maximally supersymmetric, as long as $M^5$ is smooth and preserves some supersymmetry. We investigate a specific case, $M^5=T^{1,1}$. The dual ${\cal N}=1$ SCFT, describing D3-branes at a conifold singularity, has operators that we identify with the oscillators of the light-cone string in the universal pp-wave background. The correspondence is remarkable in that it relies on the exact spectrum of anomalous dimensions in this CFT, along with the existence of certain exceptional series of operators whose dimensions are protected only in the limit of large `t Hooft coupling. We also briefly examine the singular case $M^5=S^5/Z_2$, for which the pp wave background becomes a $Z_2$ orbifold of the maximally supersymmetric background by reflection of 4 transverse coordinates. We find operators in the corresponding ${\cal N}=2$ SCFT with the right properties to describe both the untwisted and the twisted sectors of the closed string.

hep-th↗
arXiv2002

Observables of String Field Theory

We study gauge invariant operators of open string field theory and find a precise correspondence with on-shell closed strings. We provide a detailed proof of the gauge invariance of the operators and a heuristic interpretation of their correlation functions in terms of on-shell scattering amplitudes of closed strings. We also comment on the implications of these operators to vacuum string field theory.

hep-th↗
arXiv2000

Observables of Non-Commutative Gauge Theories

We construct gauge invariant operators in non-commutative gauge theories which in the IR reduce to the usual operators of ordinary field theories (e.g. F^2). We show that in the deep UV the two-point functions of these operators admit a universal exponential behavior which fits neatly with the dual supergravity results. We also consider the ratio between n-point functions and two-point functions to find exponential suppression in the UV which we compare to the high energy fixed angle scattering of string theory.

hep-th↗
arXiv2000

Large branes in AdS and their field theory dual

Recently it was suggested that a graviton in $AdS_5 \times S^5$ with a large momentum along the sphere can blow up into a spherical D-brane in $S^5$. In this paper we show that the same graviton can also blow up into a spherical D-brane in $AdS_5$ with exactly the same quantum numbers (angular momentum and energy). These branes are BPS, preserving 16 of the 32 supersymmetries. We show that there is a BPS {\it classical} solution for SYM on $S^3\times R$ with exactly the same quantum numbers. The solution has non-vanishing Higgs expectation values and hence is dual to the large brane in AdS.

hep-th↗
arXiv2000

Sphalerons, Merons and Unstable Branes in AdS

We construct unstable classical solutions of Yang-Mills theories and their dual unstable states of type IIB on AdS_5. An example is the unstable D0-brane of type IIB located at the center of AdS. This has a field theory dual which is a sphaleron in gauge theories on S^3 x R. We argue that the two are dual because both are sphalerons associated to the topology of the instanton/D-instanton. This agreement provides a non-supersymmetric test of the AdS/CFT duality. As an illustration, many aspects of Sen's hypothesis regarding the unstable branes can be seen easily in the weakly coupled dual field theory description. In Euclidean AdS the D0-branes are dual to gauge theory merons. This implies that the two ends of a D0-brane world-line carry half the charge of a D-instanton. Other examples involve unstable strings in the Coulomb phase.

hep-th↗
arXiv1999

On the Hierarchy Between Non-Commutative and Ordinary Supersymmetric Yang-Mills

Non-commutative supersymmetric Yang-Mills with rational Theta is dual to an ordinary supersymmetric Yang-Mills with a 't Hooft flux. It is believed that the simplest description is via the ordinary supersymmetric Yang-Mills. We claim, however, that the two descriptions form a hierarchy. The SYM description is the proper description in the ultra violet while the non-commutative description takes over in the infra red.

hep-th↗
arXiv1999

Non-Commutative Yang-Mills and the AdS/CFT Correspondence

We study the non-commutative supersymmetric Yang-Mills theory at strong coupling using the AdS/CFT correspondence. The supergravity description and the UV/IR relation confirms the expectation that the non-commutativity affects the ultra-violet but not the infra-red of the Yang-Mills dynamics. We show that the supergravity solution dual to the non-commutative N=4 SYM in four dimensions has no boundary and defines a minimal scale. We also show that the relation between the B field and the scale of non-commutativity is corrected at large coupling and determine its dependence on the 't Hooft coupling λ.

hep-th↗
arXiv1999

A Comment on the Entropy of Strongly Coupled N=4

We propose a field theory argument, which rests on the non-renormalization of the two point function of the energy-momentum tensor, why the ratio between the entropies of strongly coupled and weakly coupled N=4 is of order one.

hep-th↗
arXiv1999

A Comment on the Zamolodchikov c-Function and the Black String Entropy

Using the spectral representation approach to the Zamolodchikov's c-function and the Maldacena conjecture for the D1-branes, we compute the entropy of type IIB strings. An agreement, up to a numerical constant which cannot be determined using this approach, with the Bekenstein-Hawking entropy is found.

hep-th↗
arXiv1999

Black Holes, Shock Waves, and Causality in the AdS/CFT Correspondence

We find the expectation value of the energy-momentum tensor in the CFT corresponding to a moving black hole in AdS. Boosting the black hole to the speed of light, keeping the total energy fixed, yields a gravitational shock wave in AdS. The analogous procedure on the field theory side leads to ``light cone'' states, i.e., states with energy-momentum tensor localized on the light cone. The correspondence between the gravitational shock wave and these light cone states provides a useful tool for testing causality. We show, in several examples, how the CFT reproduces the causal relations in AdS.

hep-th↗
arXiv1998

D6+D0 and Five Dimensional Spinning Black Hole

We study the system of D6+D0 branes at sub-stringy scale. We show that the proper description of the system, for large background field associated with the D0-branes, is via spinning chargeless black holes in five dimensions. The repulsive force between the D6-branes and the D0-branes is understood through the centrifugal barrier. We discuss the implication on the stability of the D6+D0 solution.

hep-th↗
arXiv1998

Baryons from Supergravity

We study the construction of baryons via supergravity along the line suggested recently by Witten and by Gross and Ooguri. We calculate the energy of the baryon as a function of its size. As expected the energy is linear with N. For the non-supersymmetric theories (in three and four dimensions) we find a linear relation which is an indication of confinement. For the {\cal N} = 4 theory we obtain the result (E L= - {const.}) which is compatible with conformal invariance. Surprisingly, our calculation suggests that there is a bound state of k quarks if N\geq k\geq 5N/8. We study the {\cal N} = 4 theory also at finite temperature and find the zero temperature behavior for small size of the baryon, and screening behaviour for baryon, whose size is large compared to the thermal wavelength.

hep-th↗
arXiv1998

Supergravity Solutions for Branes Localized Within Branes

We construct supergravity solutions describing branes (D2-branes or NS5-branes or waves) localized within D6-branes in the region close to the core of the D6-branes. Other similar string-theory and M-theory `near-core' localized solutions can be found by applying U-duality and/or lifting D=10 solutions to D=11. In particular, the D2-branes localized on D6-branes is T-dual to a special case of the background describing (D)strings localized on (D)5-branes and thus is also related to a localized intersection of M2-branes and M5-branes. D6+wave configuration is U-dual to a D0-brane localized on a Kaluza-Klein 5-brane or to the fundamental string intersecting a D5-brane with the point of intersection localized on the D5-brane.

hep-th↗