Arvanitaki, Asimina, Dimopoulos, Savas, Dubovsky, Sergei, Kaloper, Nemanja, March-Russell, John
String theory suggests the simultaneous presence of many ultralight axions possibly populating each decade of mass down to the Hubble scale 10^-33eV. Conversely the presence of such a plenitude of...
Kaloper, Nemanja, Padilla, Antonio
A sizable fraction of the total energy density of the universe may be in heavy particles with a net dark $U(1)'$ charge comparable to its mass. When the charges have the same sign the cancellation...
A Natural Framework for Chaotic Inflation (2008)
Kaloper, Nemanja, Sorbo, Lorenzo
We show that inflation with a quadratic potential occurs naturally in theories where an axion-like field mixes with a 4-form. Such an axion is massive, with the mass which arises from the mixing...
Where in the String Landscape is Quintessence (2008)
Kaloper, Nemanja, Sorbo, Lorenzo
We argue that quintessence may reside in certain corners of the string landscape. It arises as a linear combination of internal space components of higher rank forms, which are axion-like at low...
Higgsflation at the GUT scale in a Higgsless Universe (2008)
Kaloper, Nemanja, Sorbo, Lorenzo, Yokoyama, Jun'ichi
We revisit inflation in induced gravity. Our focus is on models where the low scale Planck mass is completely determined by the breaking of the scaling symmetry in the field theory sector. The...
Geometric Precipices in String Cosmology (2007)
Kaloper, Nemanja, Watson, Scott
We consider the effects of graviton multiplet fields on transitions between string gas phases. Focusing on the dilaton field, we show that it may obstruct transitions between different thermodynamic...
Brane Induced Gravity: Codimension-2 (2007)
We review the results of arXiv:hep-th/0703190, on brane induced gravity (BIG) in 6D. Among a large diversity of regulated codimension-2 branes, we find that for near-critical tensions branes live...
Iglesias, Alberto, Kaloper, Nemanja, Padilla, Antonio, Park, Minjoon
We revisit the problem of defining non-minimal gravity in the first order formalism. Specializing to scalar-tensor theories, which may be disguised as `higher-derivative' models with the...
A New Perspective on DGP Gravity (2007)
Gregory, Ruth, Kaloper, Nemanja, Myers, Robert C., Padilla, Antonio
We examine brane induced gravity on codimension-1 branes, a.k.a DGP gravity, as a theory of five-dimensional gravity containing a certain class four-dimensional branes. From this perspective, the...
Challenging the Cosmological Constant (2007)
We outline a dynamical dark energy scenario whose signatures may be simultaneously tested by astronomical observations and laboratory experiments. The dark energy is a field with slightly...
How Black Holes Form in High Energy Collisions (2007)
Kaloper, Nemanja, Terning, John
We elucidate how black holes form in trans-Planckian collisions. In the rest frame of one of the incident particles, the gravitational field of the other, which is rapidly moving, looks like a...
Charting the Landscape of Modified Gravity (2007)
Kaloper, Nemanja, Kiley, Derrick
We explore brane induced gravity on a 3-brane in six locally flat dimensions. To regulate the short distance singularities in the brane core, we resolve the thin brane by a cylindrical 4-brane, with...
A New Dimension Hidden in the Shadow of a Wall (2007)
We propose a new way to hide the fifth dimension, and to modify gravity in the far infra-red. A gravitating tensional membrane in five dimensions folds the transverse space into a truncated cone,...
Evaporation of a black hole off of a tense brane (2006)
Dai, De-Chang, Kaloper, Nemanja, Starkman, Glenn D., Stojkovic, Dejan
We calculate the gray-body factors for scalar, vector and graviton fields in the background of an exact black hole localized on a tensional 3-brane in a world with two large extra dimensions. Finite...
On the new string theory inspired mechanism of generation of cosmological perturbations (2006)
Kaloper, Nemanja, Kofman, Lev, Linde, Andrei, Mukhanov, Viatcheslav
Recently a non-inflationary mechanism of generation of scale-free cosmological perturbations of metric was proposed by Brandenberger, Nayeri, and Vafa in the context of the string gas cosmology. We...
Low energy bounds on Poincare violation in causal set theory (2006)
Kaloper, Nemanja, Mattingly, David
In the causal set approach to quantum gravity, Poincar\'{e} symmetry is modified by swerving in spacetime, induced by the random lattice discretization of the space-time structure. The broken...
Charmousis, Christos, Gregory, Ruth, Kaloper, Nemanja, Padilla, Antonio
We systematically explore the spectrum of gravitational perturbations in codimension-1 DGP braneworlds, and find a 4D ghost on the self-accelerating branch of solutions. The ghost appears for any...
Exact Black Holes and Gravitational Shockwaves on Codimension-2 Branes (2006)
Kaloper, Nemanja, Kiley, Derrick
We derive exact gravitational fields of a black hole and a relativistic particle stuck on a codimension-2 brane in $D$ dimensions when gravity is ruled by the bulk $D$-dimensional Einstein-Hilbert...
Kaloper, Nemanja, Sorbo, Lorenzo
We review the pNGB quintessence models, and point out that the reason why the large decay constants $f_a \ga {\cal O}(1)M_{Pl}$ are really needed is to tame a tachyonic instability present for a wide...
Locally Localized Gravity: The Inside Story (2005)
Kaloper, Nemanja, Sorbo, Lorenzo
We derive the exact gravitational field of a relativistic particle localized on an $AdS$ 3-brane, with curvature radius $\ell$, in $AdS_5$ bulk with radius $L$. The solution is a gravitational shock...
The Accelerated Acceleration of the Universe (2005)
Csaki, Csaba, Kaloper, Nemanja, Terning, John
We present a simple mechanism which can mimic dark energy with an equation of state w < -1 as deduced from the supernova data. We imagine that the universe is accelerating under the control of a...
Gravitational Shock Waves and Their Scattering in Brane-Induced Gravity (2005)
In this paper, following hep-th/0501028, we present a detailed derivation and discussion of the exact gravitational field solutions for a relativistic particle localized on a tensional brane in...
Brane-Induced Gravity's Shocks (2005)
We construct exact gravitational field solutions for a relativistic particle localized on a tensional brane in brane-induced gravity. They are a generalization of gravitational shock waves in 4D de...
Csaki, Csaba, Kaloper, Nemanja, Terning, John
We show that the combined dimming of Type Ia supernovae induced by both a cosmological constant and the conversion of photons into axions in extra-galactic magnetic fields can impersonate dark energy...
Moduli Entrapment with Primordial Black Holes (2004)
Kaloper, Nemanja, Rahmfeld, Joachim, Sorbo, Lorenzo
We argue that primordial black holes in the early universe can provide an efficient resolution of the Brustein-Steinhardt moduli overshoot problem in string cosmology. When the universe is created...
Observational Implications of Cosmological Event Horizons (2004)
Kaloper, Nemanja, Kleban, Matthew, Sorbo, Lorenzo
In a universe dominated by a small cosmological constant or by eternal dark energy with equation of state w < -1/3, observers are surrounded by event horizons. The horizons limit how much of the...
We paste together patches of $AdS_6$ to find solutions which describe two 4-branes intersecting on a 3-brane with non-zero tension. We construct explicitly brane arrays with Minkowski, de Sitter and...
We show how short inflation naturally arises in a non-minimal gravity theory with a scalar field without any potential terms. This field drives inflation solely by its derivatives, which couple to...
Primeval Corrections to the CMB Anisotropies (2003)
Kaloper, Nemanja, Kaplinghat, Manoj
We show that deviations of the quantum state of the inflaton from the thermal vacuum of inflation may leave an imprint in the CMB anisotropies. The quantum dynamics of the inflaton in such a state...
Super-GZK Photons from Photon-Axion Mixing (2003)
Csaki, Csaba, Kaloper, Nemanja, Peloso, Marco, Terning, John
We show that photons with energies above the GZK cutoff can reach us from very distant sources if they mix with light axions in extragalactic magnetic fields. The effect which enables this is the...
Black Hole Astrophysics in AdS Braneworlds (2002)
Emparan, Roberto, Garcia-Bellido, Juan, Kaloper, Nemanja
We consider astrophysics of large black holes localized on the brane in the infinite Randall-Sundrum model. Using their description in terms of a conformal field theory (CFT) coupled to gravity,...
Black Hole Astrophysics in AdS Braneworlds (2002)
Emparan, R, García-Bellido, J, Kaloper, Nemanja
We consider astrophysics of large black holes localized on the brane in the infinite Randall-Sundrum model. Using their description in terms of a conformal field theory (CFT) coupled to gravity,...
Holographic Limitations of the Effective Field Theory of Inflation (2002)
Albrecht, Andreas, Kaloper, Nemanja, Song, Yong-Seon
Holographic considerations may provide a glimpse of quantum gravity beyond what is currently accessible by other means. Here we apply holography to inflationary cosmology. We argue that the...
Initial Conditions for Inflation (2002)
Kaloper, Nemanja, Kleban, Matthew, Lawrence, Albion, Shenker, Stephen, Susskind, Leonard
Free scalar fields in de Sitter space have a one-parameter family of states invariant under the de Sitter group, including the standard thermal vacuum. We show that, except for the thermal vacuum,...
Quantum Black Holes as Holograms in AdS Braneworlds (2002)
Emparan, R, Fabbri, A, Kaloper, Nemanja
We propose a new approach for using the AdS/CFT correspondence to study quantum black hole physics. The black holes on a brane in an AdS$_{D+1}$ braneworld that solve the classical bulk equations are...
Quantum Black Holes as Holograms in AdS Braneworlds (2002)
Emparan, Roberto, Fabbri, Alessandro, Kaloper, Nemanja
We propose a new approach for using the AdS/CFT correspondence to study quantum black hole physics. The black holes on a brane in an AdS$_{D+1}$ braneworld that solve the classical bulk equations are...
Signatures of Short Distance Physics in the Cosmic Microwave Background (2002)
Kaloper, Nemanja, Kleban, Matthew, Lawrence, Albion, Shenker, Stephen
We systematically investigate the effect of short distance physics on the spectrum of temperature anistropies in the Cosmic Microwave Background produced during inflation. We present a general...
Effects of the Intergalactic Plasma on Supernova Dimming via Photon-Axion Oscillations (2001)
Csaki, Csaba, Kaloper, Nemanja, Terning, John
We have recently proposed a mechanism of photon-axion oscillations as a way of rendering supernovae dimmer without cosmic acceleration. Subsequently, it has been argued that the intergalactic plasma...
Dimming Supernovae without Cosmic Acceleration (2001)
Csaki, Csaba, Kaloper, Nemanja, Terning, John
We present a simple model where photons propagating in extra-galactic magnetic fields can oscillate into very light axions. The oscillations may convert some of the photons departing a distant...
String Theory and Quintessence (2001)
Hellerman, Simeon, Kaloper, Nemanja, Susskind, Leonard
We discuss the obstacles for defining a set of observable quantities analogous to an S-matrix which are needed to formulate string theory in an accelerating universe. We show that the quintessence...
Gauge Symmetry and Localized Gravity in M Theory (2000)
Kaloper, Nemanja, Silverstein, Eva, Susskind, Leonard
We discuss the possibility of having gravity ``localized'' in dimension d in a system where gauge bosons propagate in dimension d+1. In such a circumstance - depending on the rate of falloff of the...
Compact Hyperbolic Extra Dimensions: Branes, Kaluza-Klein Modes and Cosmology (2000)
Kaloper, Nemanja, March-Russell, John David, Starkman, G D, Trodden, M
We reconsider theories with low gravitational (or string) scale M_* where Newton's constant is generated via new large-volume spatial dimensions, while Standard Model states are localized to a...
Compact Hyperbolic Extra Dimensions: Branes, Kaluza-Klein Modes and Cosmology (2000)
Kaloper, Nemanja, March-Russell, John, Starkman, Glenn D., Trodden, Mark
We reconsider theories with low gravitational (or string) scale M_* where Newton's constant is generated via new large-volume spatial dimensions, while Standard Model states are localized to a...
A Small Cosmological Constant from a Large Extra Dimension (2000)
Arkani-Hamed, Nima, Dimopoulos, Savas, Kaloper, Nemanja, Sundrum, Raman
We propose a new approach to the Cosmological Constant Problem which makes essential use of an extra dimension. A model is presented in which the Standard Model vacuum energy ``warps'' the...
Crystal Manyfold Universes in AdS Space (1999)
We derive crystal braneworld solutions, comprising of intersecting families of parallel $n+2$-branes in a $4+n$-dimensional $AdS$ space. Each family consists of alternating positive and negative...
Arkani-Hamed, Nima, Dimopoulos, Savas, Dvali, Gia, Kaloper, Nemanja
We propose that our world is a brane folded many times inside the sub-millimeter extra dimensions. The folding produces many connected parallel branes or folds with identical microphysics - a...
Dynamics and perturbations in assisted chaotic inflation (1999)
Kaloper, Nemanja, Liddle, Andrew R.
On compactification from higher dimensions, a single free massive scalar field gives rise to a set of effective four-dimensional scalar fields, each with a different mass. These can cooperate to...
Infinitely Large New Dimensions (1999)
Arkani-Hamed, Nima, Dimopoulos, Savas, Dvali, Gia, Kaloper, Nemanja
Infinitely Large New Dimensions (1999)
Arkani-Hamed, Nima, Dimopoulos, Savas, Dvali, Gia, Kaloper, Nemanja
We construct intersecting brane configurations in Anti-de-Sitter space localizing gravity to the intersection region, with any number $n$ of extra dimensions. This allows us to construct two kinds of...
Bent Domain Walls as Braneworlds (1999)
We consider domain walls embedded in curved backgrounds as an approximation for braneworld scenarios. We give a large class of new exact solutions, exhausting the possibilities for describing one and...
Cosmology vs. Holography (1999)
Kaloper, Nemanja, Linde, Andrei
The most radical version of the holographic principle asserts that all information about physical processes in the world can be stored on its surface. This formulation is at odds with inflationary...
Early Inflation and Cosmology in Theories with Sub-Millimeter Dimensions (1999)
Arkani-Hamed, N, Dimopoulos, Savas K, Kaloper, Nemanja, March-Russell, John David
We discuss early cosmology in theories where the fundamental Planck mass is close to the TeV scale. In such theories the standard model fields are localized to a $(3+1)$-dimensional wall with $n$ new...
Early Inflation and Cosmology in Theories with Sub-Millimeter Dimensions (1999)
Arkani-Hamed, Nima, Dimopoulos, Savas, Kaloper, Nemanja, March-Russell, John
We discuss early cosmology in theories where the fundamental Planck mass is close to the TeV scale. In such theories the standard model fields are localized to a (3+1)-dimensional wall with n new...
Rapid Asymmetric Inflation and Early Cosmology in Theories with Sub-Millimeter Dimensions (1999)
Arkani-Hamed, N, Dimopoulos, Savas K, Kaloper, Nemanja, March-Russell, John David
It was recently pointed out that the fundamental Planck mass could be close to the TeV scale with the observed weakness of gravity at long distances being due the existence of new sub-millimeter...
Rapid Asymmetric Inflation and Early Cosmology in Theories with Sub-Millimeter Dimensions (1999)
Arkani-Hamed, Nima, Dimopoulos, Savas, Kaloper, Nemanja, March-Russell, John
It was recently pointed out that the fundamental Planck mass could be close to the TeV scale with the observed weakness of gravity at long distances being due the existence of new sub-millimeter...
The O(dd) Story of Massive Supergravity (1999)
Kaloper, Nemanja, Myers, Robert C.
The low energy effective action describing the standard Kaluza-Klein reduction of heterotic string theory on a d-torus possesses a manifest O(d,d+16) symmetry. We consider generalized Scherk-Schwarz...
Inflation and Large Internal Dimensions (1998)
Kaloper, Nemanja, Linde, Andrei
We consider some aspects of inflation in models with large internal dimensions. If inflation occurs on a 3D wall after the stabilization of internal dimensions in the models with low unification...
Initial Conditions in Pre-Big Bang (1998)
This note is a summary of the work reported in hep-th/9801073. We give a brief discussion of the fine tuning problem in pre-big bang cosmology. We use the flatness problem as our test case, and in...
Topological $R^{4}$ Inflation (1998)
Ellis, Jonathan Richard, Kaloper, Nemanja, Olive, Keith A, Yokoyama, J
We consider the possibility that higher-curvature corrections in some variant of $M$ theory could drive inflation after the compactification to four dimensions. Assuming that the descent from eleven...
Topological $R^4$ Inflation (1998)
Ellis, John, Kaloper, Nemanja, Olive, Keith A., Yokoyama, Jun'ichi
We consider the possibility that higher-curvature corrections could drive inflation after the compactification to four dimensions. Assuming that the low-energy limit of the fundamental theory is...
Entropy Count for Extremal Three-Dimensional Black Strings (1998)
We compute the entropy of extremal black strings in three dimensions, using Strominger's approach to relate the Anti-de-Sitter near-horizon geometry and the conformal field theory at the asymptotic...
On Generalized Axion Reductions (1998)
Kaloper, Nemanja, Khuri, Ramzi R., Myers, Robert C.
Recently interest in using generalized reductions to construct massive supergravity theories has been revived in the context of M-theory and superstring theory. These compactifications produce mass...
Pre-Big-Bang Requires the Universe to be Exponentially Large From the Very Beginning (1998)
Kaloper, Nemanja, Linde, Andrei, Bousso, Raphael
We show that in a generic case of the pre-big-bang scenario, inflation will solve cosmological problems only if the universe at the onset of inflation is extremely large and homogeneous from the very...
Cos(M)ological Solutions in M- and String Theory (1997)
Kaloper, Nemanja, Kogan, Ian I., Olive, Keith A.
We consider solutions to the cosmological equations of motion in 11 dimensions with and without 4-form charges. We show explicitly the correspondence between some of these solutions and known...
Tailoring T-Duality Beyond the First Loop (1997)
Kaloper, Nemanja, Meissner, K A
In this article we review a recent calculation of the two-loop $\sigma$-model corrections to the T-duality map in string theory. Using the effective action approach, and focusing on backgrounds with...
Tailoring T-Duality Beyond the First Loop (1997)
Kaloper, Nemanja, Meissner, Krzysztof A.
In this article we review a recent calculation of the two-loop $\sigma$-model corrections to the T-duality map in string theory. Using the effective action approach, and focusing on backgrounds with...
Singularities In Scalar-Tensor Cosmologies (1997)
Kaloper, Nemanja, Olive, Keith A.
In this article, we examine the possibility that there exist special scalar-tensor theories of gravity with completely nonsingular FRW solutions. Our investigation in fact shows that while most...
Duality Beyond the First Loop (1997)
Kaloper, Nemanja, Meissner, K A
In this article we give a calculation of the two-loop $\si$-model corrections to the T-duality map in string theory. We use the effective action approach, and analyze two-loop corrections in a...
Duality Beyond the First Loop (1997)
Kaloper, Nemanja, Meissner, Krzysztof
In this article we give a calculation of the two-loop $\sigma$-model corrections to the T-duality map in string theory. We use the effective action approach, and analyze two-loop corrections in a...
Wavy Strings: Black or Bright? (1996)
Kaloper, Nemanja, Myers, Robert C., Roussel, Harold
Recent developments in string theory have brought forth a considerable interest in time-dependent hair on extended objects. This novel new hair is typically characterized by a wave profile along the...
Stringy Toda Cosmologies (1996)
We discuss a particular stringy modular cosmology with two axion fields in seven space-time dimensions, decomposable as a time and two flat three-spaces. The effective equations of motion for the...
Is string theory a theory of strings? (1995)
Johnson, C V, Kaloper, Nemanja, Khuri, R R, Myers, R C
Recently a great deal of evidence has been found indicating that type IIA string theory compactified on K3 is equivalent to heterotic string theory compactified on T^4. Under the transformation which...
Is string theory a theory of strings? (1995)
Johnson, Clifford V., Kaloper, Nemanja, Khuri, Ramzi R., Myers, Robert C.
Recently a great deal of evidence has been found indicating that type IIA string theory compactified on K3 is equivalent to heterotic string theory compactified on T^4. Under the transformation which...
Hidden Finite Symmetries in String Theory and Duality of Dualities (1995)
Different compactifications of six-dimensional string theory on $M_4 \times T^2$ are considered. Particular attention is given to the roles of the reduced modes as the $S$ and $T$ fields. It is shown...
A No-Go Theorem in String Cosmology (1995)
A no-go theorem pertaining to the graceful exit problem in Pre-Big-Bang inflation is reviewed. It is shown that dilaton self-interactions and string fluid sources fail to facilitate branch changing...
Towards a Singularity-Free Inflationary Universe? (1995)
Kaloper, Nemanja, Madden, Richard, Olive, Keith A.
We consider the problem of constructing a non-singular inflationary universe in stringy gravity via branch changing, from a previously superexponentially expanding phase to an FRW-like phase. Our...
New Black Strings in Three Dimensions (1995)
We present two different families of stationary black strings in three dimensions carrying electric and axion charges. Both solutions contain a singular region, which however is quite harmless for...
On Some New Black String Solutions in Three Dimensions (1995)
Anderson, Warren G., Kaloper, Nemanja
We derive several new solutions in three-dimensional stringy gravity. The solutions are obtained with the help of string duality transformations. They represent stationary configurations with...
Field Redefinitions in String Theory as a Solution Generating Technique (1994)
The purpose of this work is to show that there exists an additional invariance of the $\beta$-function equations of string theory on $d+1$-dimensional targets with $d$ toroidal isometries. It...
Topological Mass Generation in Three-Dimensional String Theory (1993)
The effective action of string theory in three dimensions is investigated, incorporating the Lorentz and gauge Chern-Simons terms in the definition of the Kalb-Ramond axion field strength. Since in...
Three Dimensional Black Holes and Four Dimensional Black Strings as Nonlinear Sigma Models (1993)
Two solutions of stringy gravity in three and four dimensions which admit interpretation as a black hole and a black string, respectively, are discussed. It is demonstrated that they are exact WZWN...
Exact Primordial Black Strings in Four Dimensions (1993)
A solution of effective string theory in four dimensions is presented which admits interpretation of a rotating black cosmic string. It is constructed by tensoring the three dimensional black hole,...
A Closed Bianchi I Universe in String Theory (1992)
A special Bianchi I universe is constructed in $~4D~$ string theory. Geometrically it represents a $~3D~$ anti-de-Sitter space crossed with a flat direction whereas in terms of an associated...
Stringy Cosmic Strings and Axion Cohomology (1992)
The static stationary axially symmetric background ("infinite cosmic string") of the $D=4$ string theory provided with an axion charge is studied in the effective theory approach. The most general...
Some general relativity from string theory / (1992)
Thesis (Ph. D.)--University of Minnesota, 1992.