arXiv subjects

Durmus Demir

Publications and source records attributed to Durmus Demir.

At least 19 recordsLinked to original sources

arXiv2023

Gauge and Poincare properties of the UV cutoff and UV completion in quantum field theory

The ultraviolet (UV) cutoff on a quantum field theory (QFT) can explicitly break or conserve the Poincare (translation) symmetry. And the very same cutoff can explicitly break or conserve the gauge symmetry. In the present work, we perform a systematic study of the UV cutoff in regard to its gauge and Poincare properties, and construct UV completions restoring the broken gauge symmetry. In the case of Poincare-conserving UV cutoff, we find that the gauge symmetry gets restored via the Higgs mechanism. In the case of Poincare-breaking UV cutoff, however, we find that the flat spacetime affine curvature takes the place of the Higgs field and, when taken to curved spacetime, gauge symmetry gets restored at the extremum of the metric-affine action. We also find that gravity emerges at the extremum if the QFT under concern consists of new particles beyond the known ones. The resulting emergent gravity plus renormalized QFT setup has the potential to reveal itself in various astrophysical, cosmological and collider phenomena.

hep-th↗

arXiv2023

Geometric Proca with Matter in Metric-Palatini Gravity

In the present work, we study linear, torsion-free metric-Palatini gravity, extended by the quadratics of the antisymmetric part of the Ricci tensor and extended also by the presence of the affine connection in the matter sector. We show that this extended metric-Palatini gravity reduces dynamically to the general relativity plus a geometrical massive vector field corresponding to non-metricity of the connection. We also show that this geometric Proca field couples to fermions universally. We derive static, spherically symmetric field equations of this Einstein-geometric Proca theory. We study possibility of black hole solutions by taking into account the presence of a dust distribution that couples to the geometric Proca. Our analytical and numerical analyses show that the presence of this dust worsens the possibility of horizon formation. We briefly discuss possible roles of this universally-coupled geometric Proca in the astrophysical and collider processes.

gr-qc↗

arXiv2023

Dimensional Regularization in Quantum Field Theory with Ultraviolet Cutoff

In view of various field-theoretic reasons, in the present work, we study the question of if the usual dimensional regularization can be extended to quantum field theories with an ultraviolet cutoff (Poincare-breaking scale) in a way preserving all the properties of the dimensional regularization. And we find that it can indeed be. The resulting extension gives a framework in which the power-law and logarithmic divergences get detached to involve different scales. This new regularization scheme, the detached regularization as we call it, enables one to treat the power-law and logarithmic divergences differently and independently. We apply the detached regularization to the computation of the vacuum energy and to two well-known QFTs namely the scalar and spinor electrodynamics. As a case study, we consider Fujikawa's subtractive renormalization in the framework of the detached regularization, and show its effectiveness up to two loops by specializing to scalar self energy. We discuss various application areas of the detached regularization.

hep-th↗

arXiv2022

Scattering Times of Quantum Particles from the Gravitational Potential, and Equivalence Principle Violation

Universality of motion under gravity, the equivalence principle, is violated for quantum particles. Here, we study time it takes for a quantum particle to scatter from the gravitational potential, and show that the scattering time, formulated here using the opportune Bohmian formulation, acts as an indicator of the equivalence principle violation. The scattering times of wavepackets are distinctive enough to distinguish between the Bohmian and Copenhagen interpretations. The scattering time of mono-energetic stationary states, formulated here as a modification of the Bohmian time by probability undercurrents, turns out to be a sensitive probe of the equivalence principle violation. We derive the quantum scattering times, and analyze equivalence principle violating terms systematically. We discuss the experimental setup needed for measuring the violation, and describe implications of a possible measurement for time in quantum theory, including the tunneling time.

quant-ph↗

arXiv2022

Tunneling time from spin fluctuations in Larmor clock

Tunneling time, time needed for a quantum particle to tunnel through a potential energy barrier, can be measured by a duration marker. One such marker is spin reorientation due to Larmor precession. With a weak magnetic field in $z$ direction, the Larmor clock reads two times, $τ_y$ and $τ_z$, for a potential energy barrier along the $y$ axis. The problem is to determine the actual tunneling time (ATT). B{ü}ttiker defines $\sqrt{τ_y^2 + τ_z^2}$ to be the ATT. Steinberg and others, on the other hand, identify $τ_y$ with the ATT. The B{ü}ttiker and Steinberg times are based on average spin components but in non-commuting spin system average of one component requires the other two to fluctuate. In the present work, we study the effects of spin fluctuations and show that the ATT can well be $τ_y + \frac{τ_z^2}{τ_y}$. We analyze the ATT candidates and reveal that the fluctuation-based ATT acts as a transmission time in all of the low-barrier, high-barrier, thick-barrier and classical dynamics limits. We extract this new ATT using the most recent experimental data by the Steinberg group. The new ATT qualifies as a viable tunneling time formula.

quant-ph↗

arXiv2021

Type-3/2 Seesaw Mechanism

Type-I seesaw provides a natural explanation for the tiny neutrino masses. The right-handed neutrino masses it requires are, however, too large to keep the Higgs boson mass at its measured value. Here we show that vector-spinors, singlet leptons like the right-handed neutrinos, generate the tiny neutrino masses naturally by the exchange of its spin-1/2 and spin-3/2 components. This one-step seesaw mechanism, which we call Type-3/2 seesaw, keeps the Higgs boson mass unchanged at one loop, and gives cause therefore to no fine-tuning problem. If the on-shell vector-spinor is a pure spin-3/2 particle then it becomes a potential candidate for hidden dark matter diluting due only to the expansion of the Universe. The Type-3/2 seesaw provides a natural framework for the neutrino, Higgs boson and dark matter sectors, with overall agreement with current experiments and observations.

hep-ph↗

arXiv2021

Naturally-Coupled Dark Sectors

The dark sector, composed of the fields neutral under the Standard Model (SM) gauge group, can couple to the SM through the Higgs, hypercharge and neutrino portals, and pull the SM towards its scale by loop corrections. This instability, not possible to prevent in the known SM completions like supersymmetry due to their sizable couplings to the SM, calls for alternative mechanisms which can neutralize sensitivities of the SM to the dark sector scale and to the ultraviolet cutoff above it. Here we review such a mechanism in which incorporation of gravity into the SM predicts the existence of a dark sector and allows it to be naturally-coupled to the SM. We discuss and illustrate salient processes which can probe the naturally-coupled dark sectors.

hep-ph↗

arXiv2021

Emergent Gravity as the Eraser of Anomalous Gauge Boson Masses, and QFT-GR Concord

In the same base setup as Sakharov's induced gravity, we investigate emergence of gravity in effective quantum field theories (QFT), with particular emphasis on the gauge sector in which gauge bosons acquire anomalous masses in proportion to the ultraviolet cutoff $Λ_\wp$. Drawing on the fact that $Λ_\wp^2$ corrections explicitly break the gauge and Poincare symmetries, we find that it is possible to map $Λ_\wp^2$ to spacetime curvature as a covariance relation and we find also that this map erases the anomalous gauge boson masses. The resulting framework describes gravity by the general relativity (GR) and matter by the QFT itself with $\logΛ_\wp$ corrections (dimensional regularization). This QFT-GR concord predicts existence of new physics beyond the Standard Model such that the new physics can be a weakly-interacting or even a non-interacting sector comprising the dark matter, dark energy and possibly more. The concord has consequential implications for collider, astrophysical and cosmological phenomena.

gr-qc↗

arXiv2020

Electroweak Stability and Discovery Luminosities for New Physics

What is the luminosity needed for discovering new physics if the electroweak scale is to remain stable? In this work we study this question, with the example of a real singlet scalar which couples to the Higgs field already at the renormalizable level. Observing that the electroweak scale remains stable if the two scalars couple in a seesawic fashion, we show that the HL-LHC, expected to deliver an integrated luminosity around 3/ab, can discover scalars weighing up to 800 GeV. The FCC-hh, on the other hand, can discover scalars as heavy as 2.3 TeV at 100/ab luminosity. It thus follows that the new physics that does not destabilize the electroweak scale can be accessed only at high luminosities, and is not possible exclude by the current LHC results.

hep-ph↗

arXiv2020

Scalar Dark Matter and Electroweak Stability

The standard model of elementary particles (SM), despite experimental completion at the LHC, needs to be extended for various physical reasons, including the cold dark matter (DM). Each extension comes with its scale and mechanism, and typically lifts, at the loop level, the electroweak scale towards its high scale. The problem is to keep the electroweak scale stable while providing a room for the aforementioned heavy extensions. To this end, it turns out that the SM Higgs sector remains stable in the presence of a heavy scalar if their quartic couplings unify at a certain scale when their masses are degenerate. Under this mass-degeneracy-driven unification (MDDU), the scalar under concern is found to qualify as a viable DM candidate and to leave the electroweak scale stable. Our detailed simulation studies explicitly show that the MDDU parameter space agrees with current collider and astrophysical bounds. Our work can be extended to other relevant scalars (like flavons, inflaton and others) as a mechanism by which the electroweak scale is held stable.

hep-ph↗

arXiv2020

Geometric Dark Matter

The dark matter, needed for various phenomena ranging from flat rotation curves to structure formation, seems to be not only neutral and long-living but also highly secluded from the ordinary matter. Here we show that, metric-affine gravity, which involves metric tensor and affine connection as two independent fields, dynamically reduces, in its minimal form, to the usual gravity plus a massive vector field. The vector, which interacts with only the quarks, leptons and gravity, is neutral and long-living (longer than the age of the Universe) when its mass range is $9.4\ {\rm MeV} < M_Y < 28.4\ {\rm MeV}$. Its scattering cross section from nucleons, which is some 60 orders of magnitude below the current bounds, is too small to facilitate direct detection of the dark matter. This property provides an explanation for whys and hows of dark matter searches. We show that due to its geometrical origin the $Y_μ$ does not couple to scalars and gauge bosons. It couples only to fermions. This very feature of the $Y_μ$ makes it fundamentally different than all the other vector dark matter candidates in the literature. The geometrical dark matter we present is minimal and self-consistent not only theoretically but also astrophysically in that its feebly interacting nature is all that is needed for its longevity.

hep-ph↗

arXiv2020

Quantum Travel Time and Tunnel Ionization Times of Atoms

Time it takes to travel from one position to another, devoid of any quantum mechanical description, has been modeled variously, especially for quantum tunneling. The model time, if universally valid, must be subluminal, must hold everywhere (inside and outside the tunneling region), must comprise interference effects, and must have a sensible classical limit. Here we show that the quantum travel time, hypothesized to emerge with the state vector, is a function of the probability density and probability current such that all the criteria above are fulfilled. We compute it inside and outside a rectangular potential barrier and find physically sensible results. Moreover, we contrast it with recent ionization time measurements of the $\rm He$ as well as the $\rm Ar$ and $\rm Kr$ atoms, and find good agreement with data. The quantum travel time holds good for stationary systems, and can have applications in numerous tunneling-driven phenomena.

quant-ph↗

arXiv2019

Symmergent Gravity, Seesawic New Physics, and their Experimental Signatures

The standard model of elementary particles (SM) suffers from various problems, such as power-law ultraviolet (UV) sensitivity, exclusion of general relativity (GR), and absence of a dark matter candidate. The LHC experiments, according to which the TeV domain appears to be empty of new particles, started sidelining TeV-scale SUSY and other known cures of the UV sensitivity. In search for a remedy, in this work, it is revealed that affine curvature can emerge in a way restoring gauge symmetries explicitly broken by the UV cutoff. This emergent curvature cures the UV sensitivity and incorporates GR as symmetry-restoring emergent gravity ({\it symmergent gravity}, in brief) if a new physics sector (NP) exists to generate the Planck scale and if SM+NP is fermi-bose balanced. This setup, carrying fingerprints of trans-Planckian SUSY, predicts that gravity is Einstein (no higher-curvature terms), cosmic/gamma rays can originate from heavy NP scalars, and the UV cutoff might take right value to suppress the cosmological constant (alleviating fine-tuning with SUSY). The NP does not have to couple to the SM. In fact, NP-SM coupling can take any value from zero to $Λ^2_{SM}/Λ^2_{NP}$ if the SM is not to jump from $Λ_{SM}\approx 500\, {\rm GeV}$ to the NP scale $Λ_{NP}$. The zero coupling, certifying an undetectable NP, agrees with all the collider and dark matter bounds at present. The {\it seesawic} bound $Λ^2_{SM}/Λ^2_{NP}$, directly verifiable at colliders, implies that: {\it (i)} dark matter must have a mass $\lesssim Λ_{SM}$, {\it (ii)} Higgs-curvature coupling must be $\approx 1.3\%$, {\it (iii)} the SM RGEs must remain nearly as in the SM, and {\it (iv)} right-handed neutrinos must have a mass $\lesssim 1000\, {\rm TeV}$. These signatures serve as a concise testbed for symmergence.

hep-ph↗

arXiv2018

Affine Inflation

Affine gravity, a gravity theory based on affine connection with no notion of metric, supports scalar field dynamics only if scalar fields have non-vanishing potential. The non-vanishing vacuum energy ensures that the cosmological constant is non-vanishing. It also ensures that the energy-momentum tensor of vacuum gives the dynamically generated metric tensor. We construct this affine setup and study primordial inflation in it. We study inflationary dynamics in affine gravity and general relativity, comparatively. We show that non-minimally coupled inflaton dynamics can be transformed into a minimally-coupled one with a modified potential. We also show that there is one unique frame in affine gravity, as opposed to the Einstein and Jordan frames in general relativity. Future observations with higher accuracy may be able to test the affine gravity.

gr-qc↗

arXiv2018

Induced Affine Inflation

Induced gravity, metrical gravity in which gravitational constant arises from vacuum expectation value of a heavy scalar, is known to suffer from Jordan frame vs. Einstein frame ambiguity, especially in inflationary dynamics. Induced gravity in affine geometry, as we show here, leads to an emergent metric and gravity scale, with no Einstein-Jordan ambiguity. While gravity is induced by the vacuum expectation value of the scalar field, nonzero vacuum energy facilitates generation of the metric. Our analysis shows that induced gravity results in a relatively large tensor-to-scalar ratio in both metrical and affine gravity setups. However, the fact remains that the induced affine gravity provides an ambiguity-free framework.

gr-qc↗

arXiv2017

Einstein Equations from Riemann-only Gravitational Actions

Here show that, pure affine actions based solely on the Riemann curvature tensor lead to Einstein field equations for gravitation. The matter and radiation involved are general enough to impose no restrictions on material dynamics or vacuum structure. This dynamical equivalence to General Relativity can be realized via also diffeomorphism breaking.

hep-th↗

arXiv2017

Statistical Approach to Tunneling Time in Attosecond Experiments

Tunneling, transport of particles through classically forbidden regions, is a pure quantum phenomenon. It governs numerous phenomena ranging from single-molecule electronics to donor-acceptor transition reactions. The main problem is the absence of a universal method to compute tunneling time. This problem has been attacked in various ways in the literature. Here, in the present work, we show that a statistical approach to the problem, motivated by the imaginary nature of time in the forbidden regions, lead to a novel tunneling time formula which is real and subluminal (in contrast to various known time definitions implying superluminal tunneling). This entropic tunneling time, as we call it, shows good agreement with the tunneling time measurements in laser-driven He ionization. Moreover, it sets an accurate range for long-range electron transfer reactions. The entropic tunneling time is general enough to extend to the photon and phonon tunneling phenomena.

quant-ph↗

arXiv2017

Naturalizing Gravity of the Quantum Fields, and the Hierarchy Problem

It is shown that gravity can be incorporated into the Standard Model (SM) in a way solving the hierarchy problem. For this, the SM effective action in flat spacetime is adapted to curved spacetime via not only the general covariance but also the gauge invariance. For the latter, gauge field hard masses, induced by loops at the UV scale $Λ$, are dispelled by construing $Λ$ as the constant value assigned to curvature. This gives way to an unprecedented mechanism for incorporating gravity into the SM in that the hierarchy problem is solved by transmutation of the Higgs boson $Λ^2$--mass into the Higgs-curvature coupling, and the cosmological constant problem is alleviated by metamorphosis of the vacuum $Λ^4$--energy into the Einstein-Hilbert term. Gravity emerges correctly if the SM is accompanied by a secluded dark sector sourcing non-interacting dark matter, dark energy and dark radiation. Physics beyond the SM, containing Higgs-phobic scalars that resolve the strong CP problem, flavor problem, baryogenesis and inflation, respects the hierarchy. Majorana neutrinos are naturally incorporated if $Λ$ lies at the see-saw scale. This mechanism, in general, leaves no compelling reason to anticipate new particles at the LHC or higher-energy colliders.

hep-ph↗